From ff6ba0db06508ec17edf5c4c8727f95a1b3886d9 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 09:38:31 +0200
Subject: [PATCH 01/16] super_errors_multi: add multi-file fixture harness with
 4 smoke fixtures

---
 .../build_tests/super_errors_multi/.gitignore |   6 +
 .../Smoke_cross_module_type_clash.expected    |  12 ++
 .../Smoke_interface_mismatch.expected         |  15 ++
 .../expected/Smoke_missing_field.expected     |   9 +
 .../Smoke_unbound_module_reference.expected   |  12 ++
 .../Smoke_cross_module_type_clash/Lib.res     |   1 +
 .../Smoke_cross_module_type_clash/User.res    |   1 +
 .../fixtures/Smoke_interface_mismatch/Foo.res |   1 +
 .../Smoke_interface_mismatch/Foo.resi         |   1 +
 .../fixtures/Smoke_missing_field/Defs.res     |   3 +
 .../fixtures/Smoke_missing_field/Use.res      |   1 +
 .../Consumer.res                              |   1 +
 tests/build_tests/super_errors_multi/input.js | 181 ++++++++++++++++++
 13 files changed, 244 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/.gitignore
 create mode 100644 tests/build_tests/super_errors_multi/expected/Smoke_cross_module_type_clash.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Smoke_interface_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Smoke_missing_field.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Smoke_unbound_module_reference.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Smoke_cross_module_type_clash/Lib.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Smoke_cross_module_type_clash/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Smoke_interface_mismatch/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Smoke_interface_mismatch/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Smoke_missing_field/Defs.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Smoke_missing_field/Use.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Smoke_unbound_module_reference/Consumer.res
 create mode 100644 tests/build_tests/super_errors_multi/input.js

diff --git a/tests/build_tests/super_errors_multi/.gitignore b/tests/build_tests/super_errors_multi/.gitignore
new file mode 100644
index 00000000000..d9d632f901c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/.gitignore
@@ -0,0 +1,6 @@
+fixtures/**/*.cmi
+fixtures/**/*.cmj
+fixtures/**/*.cmt
+fixtures/**/*.cmti
+fixtures/**/*.mjs
+fixtures/**/*.js
diff --git a/tests/build_tests/super_errors_multi/expected/Smoke_cross_module_type_clash.expected b/tests/build_tests/super_errors_multi/expected/Smoke_cross_module_type_clash.expected
new file mode 100644
index 00000000000..73cdc4f6dab
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Smoke_cross_module_type_clash.expected
@@ -0,0 +1,12 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Smoke_cross_module_type_clash/User.res:1:23-29
+
+  1 │ let v = Lib.increment("hello")
+  2 │ 
+
+  This has type: string
+  But this function argument is expecting: int
+  
+  You can convert string to int with Int.fromString.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Smoke_interface_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Smoke_interface_mismatch.expected
new file mode 100644
index 00000000000..96c0f47f00d
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Smoke_interface_mismatch.expected
@@ -0,0 +1,15 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Smoke_interface_mismatch/Foo.res:1:5
+
+  1 │ let v = "not an int"
+  2 │ 
+
+  The implementation /.../fixtures/Smoke_interface_mismatch/Foo.res
+  does not match the interface /.../fixtures/Smoke_interface_mismatch/foo.cmi:
+  Values do not match: let v: string is not included in let v: int
+  /.../fixtures/Smoke_interface_mismatch/Foo.resi:1:1-10:
+    Expected declaration
+  /.../fixtures/Smoke_interface_mismatch/Foo.res:1:5:
+    Actual declaration
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Smoke_missing_field.expected b/tests/build_tests/super_errors_multi/expected/Smoke_missing_field.expected
new file mode 100644
index 00000000000..0012f34f130
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Smoke_missing_field.expected
@@ -0,0 +1,9 @@
+===== Use.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Smoke_missing_field/Use.res:1:23-28
+
+  1 │ let bad: Defs.point = {x: 1}
+  2 │ 
+
+  Some required record fields are missing: y.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Smoke_unbound_module_reference.expected b/tests/build_tests/super_errors_multi/expected/Smoke_unbound_module_reference.expected
new file mode 100644
index 00000000000..b22c4670827
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Smoke_unbound_module_reference.expected
@@ -0,0 +1,12 @@
+===== Consumer.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Smoke_unbound_module_reference/Consumer.res:1:9-31
+
+  1 │ let x = NonexistentModule.value
+  2 │ 
+
+  The module or file NonexistentModule can't be found.
+  - If it's a third-party dependency:
+    - Did you add it to the "dependencies" or "dev-dependencies" in rescript.json?
+  - Did you include the file's directory to the "sources" in rescript.json?
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Smoke_cross_module_type_clash/Lib.res b/tests/build_tests/super_errors_multi/fixtures/Smoke_cross_module_type_clash/Lib.res
new file mode 100644
index 00000000000..9e769359ed8
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Smoke_cross_module_type_clash/Lib.res
@@ -0,0 +1 @@
+let increment = (x: int) => x + 1
diff --git a/tests/build_tests/super_errors_multi/fixtures/Smoke_cross_module_type_clash/User.res b/tests/build_tests/super_errors_multi/fixtures/Smoke_cross_module_type_clash/User.res
new file mode 100644
index 00000000000..953f935a093
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Smoke_cross_module_type_clash/User.res
@@ -0,0 +1 @@
+let v = Lib.increment("hello")
diff --git a/tests/build_tests/super_errors_multi/fixtures/Smoke_interface_mismatch/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Smoke_interface_mismatch/Foo.res
new file mode 100644
index 00000000000..618952e8492
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Smoke_interface_mismatch/Foo.res
@@ -0,0 +1 @@
+let v = "not an int"
diff --git a/tests/build_tests/super_errors_multi/fixtures/Smoke_interface_mismatch/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Smoke_interface_mismatch/Foo.resi
new file mode 100644
index 00000000000..19b83dc216f
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Smoke_interface_mismatch/Foo.resi
@@ -0,0 +1 @@
+let v: int
diff --git a/tests/build_tests/super_errors_multi/fixtures/Smoke_missing_field/Defs.res b/tests/build_tests/super_errors_multi/fixtures/Smoke_missing_field/Defs.res
new file mode 100644
index 00000000000..56a48ca98f4
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Smoke_missing_field/Defs.res
@@ -0,0 +1,3 @@
+type point = {x: int, y: int}
+
+let make = (x, y) => {x, y}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Smoke_missing_field/Use.res b/tests/build_tests/super_errors_multi/fixtures/Smoke_missing_field/Use.res
new file mode 100644
index 00000000000..ea5921fb374
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Smoke_missing_field/Use.res
@@ -0,0 +1 @@
+let bad: Defs.point = {x: 1}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Smoke_unbound_module_reference/Consumer.res b/tests/build_tests/super_errors_multi/fixtures/Smoke_unbound_module_reference/Consumer.res
new file mode 100644
index 00000000000..1a74a469eb5
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Smoke_unbound_module_reference/Consumer.res
@@ -0,0 +1 @@
+let x = NonexistentModule.value
diff --git a/tests/build_tests/super_errors_multi/input.js b/tests/build_tests/super_errors_multi/input.js
new file mode 100644
index 00000000000..ab29a789349
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/input.js
@@ -0,0 +1,181 @@
+// @ts-check
+
+import { readdirSync, statSync } from "node:fs";
+import * as fs from "node:fs/promises";
+import * as os from "node:os";
+import * as path from "node:path";
+import { setup } from "#dev/process";
+import { normalizeNewlines } from "#dev/utils";
+
+const { bsc } = setup(import.meta.dirname);
+
+const fixturesDir = path.join(import.meta.dirname, "fixtures");
+const expectedDir = path.join(import.meta.dirname, "expected");
+
+const fixtures = readdirSync(fixturesDir)
+  .filter(name => statSync(path.join(fixturesDir, name)).isDirectory())
+  .sort();
+
+const bscFlags = ["-w", "+A", "-bs-jsx", "4", "-color", "always"];
+
+const updateTests = process.argv[2] === "update";
+
+/**
+ * @param {string} fixtureName
+ * @param {string} output
+ * @return {string}
+ */
+function postProcessErrorOutput(fixtureName, output) {
+  let result = output;
+  result = result.trimEnd();
+  result = result.replace(
+    new RegExp(
+      `(?:[A-Z]:)?[\\\\/][^ ]+?tests[\\\\/]build_tests[\\\\/]super_errors_multi[\\\\/]fixtures[\\\\/]${fixtureName}[\\\\/]([^:\\s]+)`,
+      "g",
+    ),
+    (_match, file) =>
+      `/.../fixtures/${fixtureName}/${file.replace(/\\/g, "/")}`,
+  );
+  return normalizeNewlines(result);
+}
+
+/**
+ * Per-fixture artifact extensions to clean between runs so each invocation
+ * compiles against a known-empty .cmi/.cmj/.cmt set.
+ */
+const artifactExts = [".cmi", ".cmj", ".cmt", ".cmti", ".mjs", ".js"];
+
+/**
+ * @param {string} dir
+ */
+async function cleanArtifacts(dir) {
+  const entries = await fs.readdir(dir);
+  await Promise.all(
+    entries.map(async name => {
+      if (artifactExts.includes(path.extname(name))) {
+        await fs.unlink(path.join(dir, name));
+      }
+    }),
+  );
+}
+
+/**
+ * @param {string} fixtureName
+ * @returns {Promise<{ fixtureName: string, failure: string | null }>}
+ */
+async function runFixture(fixtureName) {
+  const fixtureDir = path.join(fixturesDir, fixtureName);
+
+  // Compile sources in alphabetical order, with one tweak: for any module
+  // that has both `.resi` and `.res`, the interface goes first so the
+  // implementation type-checks against the produced `.cmi`. Fixtures that
+  // need a specific dependency order across modules can prefix filenames
+  // with numeric labels (e.g. `01_Foo.res`, `02_Bar.res`).
+  const sources = (await fs.readdir(fixtureDir))
+    .filter(name => name.endsWith(".res") || name.endsWith(".resi"))
+    .sort((a, b) => {
+      const aStem = a.replace(/\.resi?$/, "");
+      const bStem = b.replace(/\.resi?$/, "");
+      if (aStem === bStem) {
+        return a.endsWith(".resi") ? -1 : 1;
+      }
+      return aStem < bStem ? -1 : aStem > bStem ? 1 : 0;
+    });
+
+  await cleanArtifacts(fixtureDir);
+
+  // Modules that have both an interface and an implementation need
+  // `-bs-read-cmi` on the implementation so the `.cmi` produced from the
+  // interface is enforced rather than overwritten.
+  const hasInterface = new Set();
+  for (const source of sources) {
+    if (source.endsWith(".resi")) hasInterface.add(source.slice(0, -5));
+  }
+
+  const chunks = [];
+  for (const source of sources) {
+    const stem = source.replace(/\.resi?$/, "");
+    const extraFlags =
+      source.endsWith(".res") && hasInterface.has(stem) ? ["-bs-read-cmi"] : [];
+    const { stderr } = await bsc(
+      [
+        ...bscFlags,
+        ...extraFlags,
+        "-I",
+        fixtureDir,
+        path.join(fixtureDir, source),
+      ],
+      { cwd: fixtureDir },
+    );
+    const stderrStr = stderr.toString();
+    if (stderrStr.length > 0) {
+      // Tag each chunk so a reader can tell which file produced which
+      // diagnostic — important when the same error gets re-emitted in the
+      // downstream consumer.
+      chunks.push(`===== ${source} =====\n${stderrStr}`);
+    }
+  }
+
+  const actualErrorOutput = postProcessErrorOutput(
+    fixtureName,
+    chunks.join("\n"),
+  );
+  const expectedFilePath = path.join(expectedDir, `${fixtureName}.expected`);
+
+  if (updateTests) {
+    await fs.writeFile(expectedFilePath, actualErrorOutput);
+    return { fixtureName, failure: null };
+  }
+
+  let expectedErrorOutput;
+  try {
+    expectedErrorOutput = postProcessErrorOutput(
+      fixtureName,
+      await fs.readFile(expectedFilePath, "utf-8"),
+    );
+  } catch {
+    return {
+      fixtureName,
+      failure: `Missing expected snapshot for ${fixtureName} (run with 'update' to create)`,
+    };
+  }
+
+  if (expectedErrorOutput === actualErrorOutput) {
+    return { fixtureName, failure: null };
+  }
+  return {
+    fixtureName,
+    failure: [
+      `The old and new error output for fixture ${fixtureName} aren't the same`,
+      "\n=== Old:",
+      expectedErrorOutput,
+      "\n=== New:",
+      actualErrorOutput,
+    ].join("\n"),
+  };
+}
+
+const concurrency = Math.max(1, os.availableParallelism());
+let cursor = 0;
+const results = new Array(fixtures.length);
+
+await Promise.all(
+  Array.from({ length: Math.min(concurrency, fixtures.length) }, async () => {
+    while (true) {
+      const i = cursor++;
+      if (i >= fixtures.length) return;
+      results[i] = await runFixture(fixtures[i]);
+    }
+  }),
+);
+
+let atLeastOneTaskFailed = false;
+for (const { failure } of results) {
+  if (failure !== null) {
+    console.error(failure);
+    atLeastOneTaskFailed = true;
+  }
+}
+if (atLeastOneTaskFailed) {
+  process.exit(1);
+}

From 35e019debfcd014fa3f8f3277579f44f6957c211 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 09:42:08 +0200
Subject: [PATCH 02/16] super_errors_multi: cover Includemod variants through
 compunit (.resi/.res signature mismatch)

---
 .../Iface_extension_constructors.expected     | 15 ++++++++++
 .../expected/Iface_missing_value.expected     | 14 +++++++++
 .../expected/Iface_modtype_infos.expected     | 30 +++++++++++++++++++
 .../expected/Iface_module_types.expected      | 22 ++++++++++++++
 .../expected/Iface_type_decl_record.expected  | 19 ++++++++++++
 .../expected/Iface_type_decl_variant.expected | 21 +++++++++++++
 .../Iface_value_descriptions.expected         | 18 +++++++++++
 .../Iface_extension_constructors/Foo.res      |  4 +++
 .../Iface_extension_constructors/Foo.resi     |  4 +++
 .../fixtures/Iface_missing_value/Foo.res      |  1 +
 .../fixtures/Iface_missing_value/Foo.resi     |  2 ++
 .../fixtures/Iface_modtype_infos/Foo.res      |  3 ++
 .../fixtures/Iface_modtype_infos/Foo.resi     |  3 ++
 .../fixtures/Iface_module_types/Foo.res       |  3 ++
 .../fixtures/Iface_module_types/Foo.resi      |  3 ++
 .../fixtures/Iface_type_decl_record/Foo.res   |  1 +
 .../fixtures/Iface_type_decl_record/Foo.resi  |  1 +
 .../fixtures/Iface_type_decl_variant/Foo.res  |  3 ++
 .../fixtures/Iface_type_decl_variant/Foo.resi |  3 ++
 .../fixtures/Iface_value_descriptions/Foo.res |  1 +
 .../Iface_value_descriptions/Foo.resi         |  1 +
 21 files changed, 172 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_extension_constructors.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_missing_value.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_modtype_infos.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_module_types.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_type_decl_record.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_type_decl_variant.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_value_descriptions.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_extension_constructors/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_extension_constructors/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_missing_value/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_missing_value/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_modtype_infos/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_modtype_infos/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_module_types/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_module_types/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_record/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_record/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_variant/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_variant/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_value_descriptions/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_value_descriptions/Foo.resi

diff --git a/tests/build_tests/super_errors_multi/expected/Iface_extension_constructors.expected b/tests/build_tests/super_errors_multi/expected/Iface_extension_constructors.expected
new file mode 100644
index 00000000000..ac624fa56ff
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_extension_constructors.expected
@@ -0,0 +1,15 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_extension_constructors/Foo.res
+
+  The implementation /.../fixtures/Iface_extension_constructors/Foo.res
+  does not match the interface /.../fixtures/Iface_extension_constructors/foo.cmi:
+  Extension declarations do not match:
+    type t +=  Boom(string)
+  is not included in
+    type t +=  Boom(int)
+  /.../fixtures/Iface_extension_constructors/Foo.res:
+    Expected declaration
+  /.../fixtures/Iface_extension_constructors/Foo.res:4:3-16:
+    Actual declaration
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_missing_value.expected b/tests/build_tests/super_errors_multi/expected/Iface_missing_value.expected
new file mode 100644
index 00000000000..b69da19d07c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_missing_value.expected
@@ -0,0 +1,14 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_missing_value/Foo.resi:2:1-13
+
+  1 │ let a: int
+  2 │ let b: string
+  3 │ 
+
+  The implementation /.../fixtures/Iface_missing_value/Foo.res
+  does not match the interface /.../fixtures/Iface_missing_value/foo.cmi:
+  The value `b' is required but not provided
+  /.../fixtures/Iface_missing_value/Foo.resi:2:1-13:
+    Expected declaration
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_modtype_infos.expected b/tests/build_tests/super_errors_multi/expected/Iface_modtype_infos.expected
new file mode 100644
index 00000000000..2cf2a858fbf
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_modtype_infos.expected
@@ -0,0 +1,30 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_modtype_infos/Foo.res
+
+  The implementation /.../fixtures/Iface_modtype_infos/Foo.res
+  does not match the interface /.../fixtures/Iface_modtype_infos/foo.cmi:
+  Module type declarations do not match:
+    module type T = {
+  let v: string
+}
+  does not match
+    module type T = {
+  let v: int
+}
+  At position module type T = <here>
+  Modules do not match:
+    {
+  let v: string
+}
+  is not included in
+    {
+  let v: int
+}
+  At position module type T = <here>
+  Values do not match: let v: string is not included in let v: int
+  /.../fixtures/Iface_modtype_infos/Foo.resi:2:3-12:
+    Expected declaration
+  /.../fixtures/Iface_modtype_infos/Foo.res:2:3-15:
+    Actual declaration
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_module_types.expected b/tests/build_tests/super_errors_multi/expected/Iface_module_types.expected
new file mode 100644
index 00000000000..6276a98fcd1
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_module_types.expected
@@ -0,0 +1,22 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_module_types/Foo.res
+
+  The implementation /.../fixtures/Iface_module_types/Foo.res
+  does not match the interface /.../fixtures/Iface_module_types/foo.cmi:
+  In module Inner:
+  Modules do not match:
+    {
+  let value: string
+}
+  is not included in
+    {
+  let value: int
+}
+  In module Inner:
+  Values do not match: let value: string is not included in let value: int
+  /.../fixtures/Iface_module_types/Foo.resi:2:3-16:
+    Expected declaration
+  /.../fixtures/Iface_module_types/Foo.res:2:7-11:
+    Actual declaration
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_type_decl_record.expected b/tests/build_tests/super_errors_multi/expected/Iface_type_decl_record.expected
new file mode 100644
index 00000000000..16ea04ada1a
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_type_decl_record.expected
@@ -0,0 +1,19 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_type_decl_record/Foo.res:1:1-25
+
+  1 │ type t = {x: int, z: int}
+  2 │ 
+
+  The implementation /.../fixtures/Iface_type_decl_record/Foo.res
+  does not match the interface /.../fixtures/Iface_type_decl_record/foo.cmi:
+  Type declarations do not match:
+    type t = {x: int, z: int}
+  is not included in
+    type t = {x: int, y: int}
+  /.../fixtures/Iface_type_decl_record/Foo.resi:1:1-25:
+    Expected declaration
+  /.../fixtures/Iface_type_decl_record/Foo.res:1:1-25:
+    Actual declaration
+  Fields number 2 have different names, z and y.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_type_decl_variant.expected b/tests/build_tests/super_errors_multi/expected/Iface_type_decl_variant.expected
new file mode 100644
index 00000000000..e3d5b75c8d4
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_type_decl_variant.expected
@@ -0,0 +1,21 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_type_decl_variant/Foo.res:1:1-3:13
+
+  1 │ type t =
+  2 │   | A
+  3 │   | B(string)
+  4 │ 
+
+  The implementation /.../fixtures/Iface_type_decl_variant/Foo.res
+  does not match the interface /.../fixtures/Iface_type_decl_variant/foo.cmi:
+  Type declarations do not match:
+    type t = A | B(string)
+  is not included in
+    type t = A | B(int)
+  /.../fixtures/Iface_type_decl_variant/Foo.resi:1:1-3:10:
+    Expected declaration
+  /.../fixtures/Iface_type_decl_variant/Foo.res:1:1-3:13:
+    Actual declaration
+  The types for field B are not equal.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_value_descriptions.expected b/tests/build_tests/super_errors_multi/expected/Iface_value_descriptions.expected
new file mode 100644
index 00000000000..6f9df31b053
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_value_descriptions.expected
@@ -0,0 +1,18 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_value_descriptions/Foo.res:1:5-11
+
+  1 │ let compute = (s: string) => String.length(s)
+  2 │ 
+
+  The implementation /.../fixtures/Iface_value_descriptions/Foo.res
+  does not match the interface /.../fixtures/Iface_value_descriptions/foo.cmi:
+  Values do not match:
+    let compute: string => int
+  is not included in
+    let compute: int => int
+  /.../fixtures/Iface_value_descriptions/Foo.resi:1:1-23:
+    Expected declaration
+  /.../fixtures/Iface_value_descriptions/Foo.res:1:5-11:
+    Actual declaration
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_extension_constructors/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_extension_constructors/Foo.res
new file mode 100644
index 00000000000..3caf4e6f3d4
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_extension_constructors/Foo.res
@@ -0,0 +1,4 @@
+type t = ..
+
+type t +=
+  | Boom(string)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_extension_constructors/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_extension_constructors/Foo.resi
new file mode 100644
index 00000000000..47a74f838dd
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_extension_constructors/Foo.resi
@@ -0,0 +1,4 @@
+type t = ..
+
+type t +=
+  | Boom(int)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_missing_value/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_missing_value/Foo.res
new file mode 100644
index 00000000000..67bbe3ba8e7
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_missing_value/Foo.res
@@ -0,0 +1 @@
+let a = 1
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_missing_value/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_missing_value/Foo.resi
new file mode 100644
index 00000000000..0fb0b0c7e85
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_missing_value/Foo.resi
@@ -0,0 +1,2 @@
+let a: int
+let b: string
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_modtype_infos/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_modtype_infos/Foo.res
new file mode 100644
index 00000000000..708a6eb23ec
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_modtype_infos/Foo.res
@@ -0,0 +1,3 @@
+module type T = {
+  let v: string
+}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_modtype_infos/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_modtype_infos/Foo.resi
new file mode 100644
index 00000000000..4d77f569616
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_modtype_infos/Foo.resi
@@ -0,0 +1,3 @@
+module type T = {
+  let v: int
+}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_module_types/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_module_types/Foo.res
new file mode 100644
index 00000000000..086f64fce1b
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_module_types/Foo.res
@@ -0,0 +1,3 @@
+module Inner = {
+  let value = "not an int"
+}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_module_types/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_module_types/Foo.resi
new file mode 100644
index 00000000000..c1c80261e51
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_module_types/Foo.resi
@@ -0,0 +1,3 @@
+module Inner: {
+  let value: int
+}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_record/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_record/Foo.res
new file mode 100644
index 00000000000..3bb325d27a1
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_record/Foo.res
@@ -0,0 +1 @@
+type t = {x: int, z: int}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_record/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_record/Foo.resi
new file mode 100644
index 00000000000..b5eab822459
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_record/Foo.resi
@@ -0,0 +1 @@
+type t = {x: int, y: int}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_variant/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_variant/Foo.res
new file mode 100644
index 00000000000..a968c4a7333
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_variant/Foo.res
@@ -0,0 +1,3 @@
+type t =
+  | A
+  | B(string)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_variant/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_variant/Foo.resi
new file mode 100644
index 00000000000..94e648c4224
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_type_decl_variant/Foo.resi
@@ -0,0 +1,3 @@
+type t =
+  | A
+  | B(int)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_value_descriptions/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_value_descriptions/Foo.res
new file mode 100644
index 00000000000..b6c3061ea61
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_value_descriptions/Foo.res
@@ -0,0 +1 @@
+let compute = (s: string) => String.length(s)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_value_descriptions/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_value_descriptions/Foo.resi
new file mode 100644
index 00000000000..aec7b21274f
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_value_descriptions/Foo.resi
@@ -0,0 +1 @@
+let compute: int => int

From ba0a78ab65d36fa2e395dd216612aa70b65b48f2 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 09:45:54 +0200
Subject: [PATCH 03/16] super_errors_multi: cover cross-module type / record /
 constructor disambiguation errors

---
 .../Cross_abstract_type_construction.expected        | 10 ++++++++++
 .../expected/Cross_chain_of_aliases.expected         | 12 ++++++++++++
 .../expected/Cross_dependent_clash.expected          |  9 +++++++++
 .../Cross_module_record_disambiguation.expected      | 11 +++++++++++
 .../Cross_qualified_constructor_mismatch.expected    | 10 ++++++++++
 .../Cross_abstract_type_construction/Abs.res         |  3 +++
 .../Cross_abstract_type_construction/Abs.resi        |  3 +++
 .../Cross_abstract_type_construction/User.res        |  1 +
 .../fixtures/Cross_chain_of_aliases/A.res            |  4 ++++
 .../fixtures/Cross_chain_of_aliases/B.res            |  1 +
 .../fixtures/Cross_chain_of_aliases/C.res            |  1 +
 .../fixtures/Cross_dependent_clash/Sender.res        |  3 +++
 .../fixtures/Cross_dependent_clash/User.res          |  1 +
 .../Cross_module_record_disambiguation/Box.res       |  1 +
 .../Cross_module_record_disambiguation/Point.res     |  1 +
 .../Cross_module_record_disambiguation/User.res      |  1 +
 .../Cross_qualified_constructor_mismatch/Color.res   |  3 +++
 .../Cross_qualified_constructor_mismatch/Shape.res   |  3 +++
 .../Cross_qualified_constructor_mismatch/User.res    |  1 +
 19 files changed, 79 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_abstract_type_construction.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_chain_of_aliases.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_dependent_clash.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_module_record_disambiguation.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_qualified_constructor_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/Abs.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/Abs.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/A.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/B.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/C.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_dependent_clash/Sender.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_dependent_clash/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/Box.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/Point.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/Color.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/Shape.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/User.res

diff --git a/tests/build_tests/super_errors_multi/expected/Cross_abstract_type_construction.expected b/tests/build_tests/super_errors_multi/expected/Cross_abstract_type_construction.expected
new file mode 100644
index 00000000000..c3c8d10770b
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_abstract_type_construction.expected
@@ -0,0 +1,10 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_abstract_type_construction/User.res:1:18
+
+  1 │ let bad: Abs.t = 1
+  2 │ 
+
+  This has type: int
+  But it's expected to have type: Abs.t
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_chain_of_aliases.expected b/tests/build_tests/super_errors_multi/expected/Cross_chain_of_aliases.expected
new file mode 100644
index 00000000000..2b762fd2a92
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_chain_of_aliases.expected
@@ -0,0 +1,12 @@
+===== C.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_chain_of_aliases/C.res:1:23-29
+
+  1 │ let v: B.Reexport.t = "wrong"
+  2 │ 
+
+  This has type: string
+  But it's expected to have type: B.Reexport.t (defined as int)
+  
+  You can convert string to int with Int.fromString.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_dependent_clash.expected b/tests/build_tests/super_errors_multi/expected/Cross_dependent_clash.expected
new file mode 100644
index 00000000000..479acd93378
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_dependent_clash.expected
@@ -0,0 +1,9 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_dependent_clash/User.res:1:21-34
+
+  1 │ let _ = Sender.send({to_: "alice"})
+  2 │ 
+
+  Some required record fields are missing: body.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_module_record_disambiguation.expected b/tests/build_tests/super_errors_multi/expected/Cross_module_record_disambiguation.expected
new file mode 100644
index 00000000000..33e0bdfb778
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_module_record_disambiguation.expected
@@ -0,0 +1,11 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_module_record_disambiguation/User.res:1:19-23
+
+  1 │ let r: Point.t = {width: 1, height: 2}
+  2 │ 
+
+  The field width does not belong to type Point.t
+  
+  This record expression is expected to have type Point.t
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_qualified_constructor_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Cross_qualified_constructor_mismatch.expected
new file mode 100644
index 00000000000..f89b459b4eb
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_qualified_constructor_mismatch.expected
@@ -0,0 +1,10 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_qualified_constructor_mismatch/User.res:1:18-26
+
+  1 │ let v: Shape.t = Color.Red
+  2 │ 
+
+  The constructor Color.Red belongs to the variant type Color.t
+  but a constructor was expected belonging to the variant type Shape.t
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/Abs.res b/tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/Abs.res
new file mode 100644
index 00000000000..144d9bb482c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/Abs.res
@@ -0,0 +1,3 @@
+type t = int
+
+let make = v => v
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/Abs.resi b/tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/Abs.resi
new file mode 100644
index 00000000000..5c236fb1c87
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/Abs.resi
@@ -0,0 +1,3 @@
+type t
+
+let make: int => t
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/User.res
new file mode 100644
index 00000000000..4d423a447b3
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_abstract_type_construction/User.res
@@ -0,0 +1 @@
+let bad: Abs.t = 1
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/A.res b/tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/A.res
new file mode 100644
index 00000000000..23d13e567bc
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/A.res
@@ -0,0 +1,4 @@
+module Inner = {
+  type t = int
+  let v = 0
+}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/B.res b/tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/B.res
new file mode 100644
index 00000000000..d2ede9cbaa0
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/B.res
@@ -0,0 +1 @@
+module Reexport = A.Inner
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/C.res b/tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/C.res
new file mode 100644
index 00000000000..a2ceb98aea6
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_chain_of_aliases/C.res
@@ -0,0 +1 @@
+let v: B.Reexport.t = "wrong"
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_dependent_clash/Sender.res b/tests/build_tests/super_errors_multi/fixtures/Cross_dependent_clash/Sender.res
new file mode 100644
index 00000000000..26c6349dfed
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_dependent_clash/Sender.res
@@ -0,0 +1,3 @@
+type message = {to_: string, body: string}
+
+let send: message => unit = _msg => ()
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_dependent_clash/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_dependent_clash/User.res
new file mode 100644
index 00000000000..0dd83b5b4b4
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_dependent_clash/User.res
@@ -0,0 +1 @@
+let _ = Sender.send({to_: "alice"})
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/Box.res b/tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/Box.res
new file mode 100644
index 00000000000..6915e332a3d
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/Box.res
@@ -0,0 +1 @@
+type t = {width: int, height: int}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/Point.res b/tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/Point.res
new file mode 100644
index 00000000000..b5eab822459
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/Point.res
@@ -0,0 +1 @@
+type t = {x: int, y: int}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/User.res
new file mode 100644
index 00000000000..dbde9b1c866
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_module_record_disambiguation/User.res
@@ -0,0 +1 @@
+let r: Point.t = {width: 1, height: 2}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/Color.res b/tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/Color.res
new file mode 100644
index 00000000000..efc0eae0b5f
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/Color.res
@@ -0,0 +1,3 @@
+type t =
+  | Red
+  | Green
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/Shape.res b/tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/Shape.res
new file mode 100644
index 00000000000..36d3a19172c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/Shape.res
@@ -0,0 +1,3 @@
+type t =
+  | Circle
+  | Square
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/User.res
new file mode 100644
index 00000000000..a809c8d4cae
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_qualified_constructor_mismatch/User.res
@@ -0,0 +1 @@
+let v: Shape.t = Color.Red

From cf5519f3ea06c3bf46ddef172bd21ca2903bb2c0 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 09:48:44 +0200
Subject: [PATCH 04/16] super_errors_multi: cover cross-module external,
 private constructor, unused open

---
 .../Cross_external_argument_clash.expected    | 12 ++++++++
 .../Cross_jsx_component_wrong_prop.expected   | 29 ++++++++++++++++++
 ...Cross_private_constructor_pattern.expected | 30 +++++++++++++++++++
 .../expected/Cross_unused_open.expected       | 10 +++++++
 .../Cross_external_argument_clash/Ffi.res     |  1 +
 .../Cross_external_argument_clash/User.res    |  1 +
 .../Result.res                                |  5 ++++
 .../Result.resi                               |  6 ++++
 .../User.res                                  |  1 +
 .../fixtures/Cross_unused_open/Helpers.res    |  1 +
 .../fixtures/Cross_unused_open/User.res       |  3 ++
 11 files changed, 99 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_external_argument_clash.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_jsx_component_wrong_prop.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_private_constructor_pattern.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_unused_open.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_external_argument_clash/Ffi.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_external_argument_clash/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/Result.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/Result.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_unused_open/Helpers.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_unused_open/User.res

diff --git a/tests/build_tests/super_errors_multi/expected/Cross_external_argument_clash.expected b/tests/build_tests/super_errors_multi/expected/Cross_external_argument_clash.expected
new file mode 100644
index 00000000000..7c8ec25834d
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_external_argument_clash.expected
@@ -0,0 +1,12 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_external_argument_clash/User.res:1:22-23
+
+  1 │ let x = Ffi.parseInt(42)
+  2 │ 
+
+  This has type: int
+  But this function argument is expecting: string
+  
+  You can convert int to string with Int.toString.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_jsx_component_wrong_prop.expected b/tests/build_tests/super_errors_multi/expected/Cross_jsx_component_wrong_prop.expected
new file mode 100644
index 00000000000..273f3d80e89
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_jsx_component_wrong_prop.expected
@@ -0,0 +1,29 @@
+===== App.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_jsx_component_wrong_prop/App.res:2:18-36
+
+  1 │ @react.component
+  2 │ let make = () => <Button label=42 />
+  3 │ 
+
+  The module or file React can't be found.
+  - If it's a third-party dependency:
+    - Did you add it to the "dependencies" or "dev-dependencies" in rescript.json?
+  - Did you include the file's directory to the "sources" in rescript.json?
+  
+
+
+===== Button.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_jsx_component_wrong_prop/Button.res:2:32-50
+
+  1 │ @react.component
+  2 │ let make = (~label: string) => React.string(label)
+  3 │ 
+
+  The module or file React can't be found.
+  - If it's a third-party dependency:
+    - Did you add it to the "dependencies" or "dev-dependencies" in rescript.json?
+  - Did you include the file's directory to the "sources" in rescript.json?
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_private_constructor_pattern.expected b/tests/build_tests/super_errors_multi/expected/Cross_private_constructor_pattern.expected
new file mode 100644
index 00000000000..ef3cce1c239
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_private_constructor_pattern.expected
@@ -0,0 +1,30 @@
+===== Result.res =====
+
+  Warning number 37
+  /.../fixtures/Cross_private_constructor_pattern/Result.res:1:1-3:11
+
+  1 │ type t =
+  2 │   | Loaded(string)
+  3 │   | Loading
+  4 │ 
+  5 │ let loaded = s => Loaded(s)
+
+  constructor Loading is never used to build values.
+Its type is exported as a private type.
+
+
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_private_constructor_pattern/User.res:1:9-21
+
+  1 │ let x = Result.Loaded("hello")
+  2 │ 
+
+  The variant constructor Result.Loaded can't be found.
+  
+  - If it's defined in another module or file, bring it into scope by:
+    - Prefixing it with said module name: TheModule.Result.Loaded
+    - Or specifying its type: let theValue: TheModule.theType = Result.Loaded
+  - Constructors and modules are both capitalized. Did you want the latter?
+    Then instead of let foo = Bar, try module Foo = Bar.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_unused_open.expected b/tests/build_tests/super_errors_multi/expected/Cross_unused_open.expected
new file mode 100644
index 00000000000..6ceb8001ecc
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_unused_open.expected
@@ -0,0 +1,10 @@
+===== User.res =====
+
+  Warning number 33
+  /.../fixtures/Cross_unused_open/User.res:1:1-12
+
+  1 │ open Helpers
+  2 │ 
+  3 │ let v = 42
+
+  unused open Helpers.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_external_argument_clash/Ffi.res b/tests/build_tests/super_errors_multi/fixtures/Cross_external_argument_clash/Ffi.res
new file mode 100644
index 00000000000..ce430fb62ea
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_external_argument_clash/Ffi.res
@@ -0,0 +1 @@
+@val external parseInt: string => int = "parseInt"
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_external_argument_clash/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_external_argument_clash/User.res
new file mode 100644
index 00000000000..5957ea12fca
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_external_argument_clash/User.res
@@ -0,0 +1 @@
+let x = Ffi.parseInt(42)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/Result.res b/tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/Result.res
new file mode 100644
index 00000000000..4f7e62c517f
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/Result.res
@@ -0,0 +1,5 @@
+type t =
+  | Loaded(string)
+  | Loading
+
+let loaded = s => Loaded(s)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/Result.resi b/tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/Result.resi
new file mode 100644
index 00000000000..368723838f6
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/Result.resi
@@ -0,0 +1,6 @@
+type t =
+  private
+  | Loaded(string)
+  | Loading
+
+let loaded: string => t
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/User.res
new file mode 100644
index 00000000000..7233bf7c71e
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_private_constructor_pattern/User.res
@@ -0,0 +1 @@
+let x = Result.Loaded("hello")
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_unused_open/Helpers.res b/tests/build_tests/super_errors_multi/fixtures/Cross_unused_open/Helpers.res
new file mode 100644
index 00000000000..eda5ab91406
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_unused_open/Helpers.res
@@ -0,0 +1 @@
+let unrelated = 1
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_unused_open/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_unused_open/User.res
new file mode 100644
index 00000000000..55d4ee7d67c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_unused_open/User.res
@@ -0,0 +1,3 @@
+open Helpers
+
+let v = 42

From 98b3e68b19890c51871f7ca427e1b55db75c7e24 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 09:48:55 +0200
Subject: [PATCH 05/16] super_errors_multi: drop orphan JSX expected snapshot

---
 .../Cross_jsx_component_wrong_prop.expected   | 29 -------------------
 1 file changed, 29 deletions(-)
 delete mode 100644 tests/build_tests/super_errors_multi/expected/Cross_jsx_component_wrong_prop.expected

diff --git a/tests/build_tests/super_errors_multi/expected/Cross_jsx_component_wrong_prop.expected b/tests/build_tests/super_errors_multi/expected/Cross_jsx_component_wrong_prop.expected
deleted file mode 100644
index 273f3d80e89..00000000000
--- a/tests/build_tests/super_errors_multi/expected/Cross_jsx_component_wrong_prop.expected
+++ /dev/null
@@ -1,29 +0,0 @@
-===== App.res =====
-
-  We've found a bug for you!
-  /.../fixtures/Cross_jsx_component_wrong_prop/App.res:2:18-36
-
-  1 │ @react.component
-  2 │ let make = () => <Button label=42 />
-  3 │ 
-
-  The module or file React can't be found.
-  - If it's a third-party dependency:
-    - Did you add it to the "dependencies" or "dev-dependencies" in rescript.json?
-  - Did you include the file's directory to the "sources" in rescript.json?
-  
-
-
-===== Button.res =====
-
-  We've found a bug for you!
-  /.../fixtures/Cross_jsx_component_wrong_prop/Button.res:2:32-50
-
-  1 │ @react.component
-  2 │ let make = (~label: string) => React.string(label)
-  3 │ 
-
-  The module or file React can't be found.
-  - If it's a third-party dependency:
-    - Did you add it to the "dependencies" or "dev-dependencies" in rescript.json?
-  - Did you include the file's directory to the "sources" in rescript.json?
\ No newline at end of file

From d8e76af8e0ebe5d5c83daf392b8f9db2916e096c Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 10:05:42 +0200
Subject: [PATCH 06/16] super_errors_multi: cover cross-module deprecation,
 open-shadows, label-constructor disambiguation

---
 .../expected/Cross_deprecated_type.expected   | 10 ++++++++
 .../expected/Cross_deprecated_value.expected  | 10 ++++++++
 ...ule_open_shadow_label_constructor.expected | 24 +++++++++++++++++++
 .../Cross_open_shadows_identifier.expected    | 11 +++++++++
 .../fixtures/Cross_deprecated_type/Legacy.res |  2 ++
 .../fixtures/Cross_deprecated_type/User.res   |  1 +
 .../Cross_deprecated_value/Legacy.res         |  2 ++
 .../fixtures/Cross_deprecated_value/User.res  |  1 +
 .../A.res                                     |  3 +++
 .../User.res                                  |  7 ++++++
 .../Cross_open_shadows_identifier/A.res       |  1 +
 .../Cross_open_shadows_identifier/User.res    |  3 +++
 tests/build_tests/super_errors_multi/input.js | 13 +++++++++-
 13 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_deprecated_type.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_deprecated_value.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_module_open_shadow_label_constructor.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_open_shadows_identifier.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_type/Legacy.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_type/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_value/Legacy.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_value/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_module_open_shadow_label_constructor/A.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_module_open_shadow_label_constructor/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_open_shadows_identifier/A.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_open_shadows_identifier/User.res

diff --git a/tests/build_tests/super_errors_multi/expected/Cross_deprecated_type.expected b/tests/build_tests/super_errors_multi/expected/Cross_deprecated_type.expected
new file mode 100644
index 00000000000..8c4bb3af7b6
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_deprecated_type.expected
@@ -0,0 +1,10 @@
+===== User.res =====
+
+  Warning number 3
+  /.../fixtures/Cross_deprecated_type/User.res:1:8-15
+
+  1 │ let v: Legacy.t = 1
+  2 │ 
+
+  deprecated: Legacy.t
+  Use newType instead
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_deprecated_value.expected b/tests/build_tests/super_errors_multi/expected/Cross_deprecated_value.expected
new file mode 100644
index 00000000000..79d17efb7cd
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_deprecated_value.expected
@@ -0,0 +1,10 @@
+===== User.res =====
+
+  Warning number 3
+  /.../fixtures/Cross_deprecated_value/User.res:1:9-22
+
+  1 │ let x = Legacy.compute(1)
+  2 │ 
+
+  deprecated: Legacy.compute
+  Use computeNew instead
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_module_open_shadow_label_constructor.expected b/tests/build_tests/super_errors_multi/expected/Cross_module_open_shadow_label_constructor.expected
new file mode 100644
index 00000000000..8831e4634fc
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_module_open_shadow_label_constructor.expected
@@ -0,0 +1,24 @@
+===== User.res =====
+
+  Warning number 45
+  /.../fixtures/Cross_module_open_shadow_label_constructor/User.res:5:1-6
+
+  3 │   | Bar
+  4 │ 
+  5 │ open A
+  6 │ 
+  7 │ let v = Foo
+
+  this open statement shadows the constructor Foo (which is later used)
+
+
+  Warning number 41
+  /.../fixtures/Cross_module_open_shadow_label_constructor/User.res:7:9-11
+
+  5 │ open A
+  6 │ 
+  7 │ let v = Foo
+  8 │ 
+
+  Foo belongs to several types: A.t t
+The first one was selected. Disambiguate if this is wrong.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_open_shadows_identifier.expected b/tests/build_tests/super_errors_multi/expected/Cross_open_shadows_identifier.expected
new file mode 100644
index 00000000000..f0778408966
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_open_shadows_identifier.expected
@@ -0,0 +1,11 @@
+===== User.res =====
+
+  Warning number 44
+  /.../fixtures/Cross_open_shadows_identifier/User.res:2:1-6
+
+  1 │ let answer = "outer"
+  2 │ open A
+  3 │ let _ = answer
+  4 │ 
+
+  this open statement shadows the value identifier answer (which is later used)
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_type/Legacy.res b/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_type/Legacy.res
new file mode 100644
index 00000000000..53e551b132c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_type/Legacy.res
@@ -0,0 +1,2 @@
+@deprecated("Use newType instead")
+type t = int
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_type/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_type/User.res
new file mode 100644
index 00000000000..2b8956acb5f
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_type/User.res
@@ -0,0 +1 @@
+let v: Legacy.t = 1
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_value/Legacy.res b/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_value/Legacy.res
new file mode 100644
index 00000000000..b827ea2d042
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_value/Legacy.res
@@ -0,0 +1,2 @@
+@deprecated("Use computeNew instead") @val
+external compute: int => int = "compute"
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_value/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_value/User.res
new file mode 100644
index 00000000000..7df87bdf2c4
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_deprecated_value/User.res
@@ -0,0 +1 @@
+let x = Legacy.compute(1)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_module_open_shadow_label_constructor/A.res b/tests/build_tests/super_errors_multi/fixtures/Cross_module_open_shadow_label_constructor/A.res
new file mode 100644
index 00000000000..0f13949afd9
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_module_open_shadow_label_constructor/A.res
@@ -0,0 +1,3 @@
+type t =
+  | Foo
+  | Bar
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_module_open_shadow_label_constructor/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_module_open_shadow_label_constructor/User.res
new file mode 100644
index 00000000000..47b8a41a2b2
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_module_open_shadow_label_constructor/User.res
@@ -0,0 +1,7 @@
+type t =
+  | Foo
+  | Bar
+
+open A
+
+let v = Foo
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_open_shadows_identifier/A.res b/tests/build_tests/super_errors_multi/fixtures/Cross_open_shadows_identifier/A.res
new file mode 100644
index 00000000000..cd298427b25
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_open_shadows_identifier/A.res
@@ -0,0 +1 @@
+let answer = 42
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_open_shadows_identifier/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_open_shadows_identifier/User.res
new file mode 100644
index 00000000000..2c518455ed2
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_open_shadows_identifier/User.res
@@ -0,0 +1,3 @@
+let answer = "outer"
+open A
+let _ = answer
diff --git a/tests/build_tests/super_errors_multi/input.js b/tests/build_tests/super_errors_multi/input.js
index ab29a789349..899f93170fb 100644
--- a/tests/build_tests/super_errors_multi/input.js
+++ b/tests/build_tests/super_errors_multi/input.js
@@ -16,7 +16,18 @@ const fixtures = readdirSync(fixturesDir)
   .filter(name => statSync(path.join(fixturesDir, name)).isDirectory())
   .sort();
 
-const bscFlags = ["-w", "+A", "-bs-jsx", "4", "-color", "always"];
+// `-bs-cmi-only` stops the pipeline after typechecking. Without it, bsc tries
+// to emit .mjs and resolve sibling .js files for cross-module imports, which
+// fails in this harness because we don't run the build system.
+const bscFlags = [
+  "-w",
+  "+A",
+  "-bs-jsx",
+  "4",
+  "-color",
+  "always",
+  "-bs-cmi-only",
+];
 
 const updateTests = process.argv[2] === "update";
 

From 9ec14054c5efd7b21faf5146d3f599e7a1991806 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 10:08:00 +0200
Subject: [PATCH 07/16] super_errors_multi: cover typemod
 Interface_not_compiled

---
 scripts/format.sh                              |  2 +-
 scripts/format_check.sh                        |  2 +-
 .../expected/Iface_not_compiled.expected       | 18 ++++++++++++++++++
 .../fixtures/Iface_not_compiled/Foo.res        |  1 +
 .../fixtures/Iface_not_compiled/Foo.resi       |  1 +
 5 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_not_compiled.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/Foo.resi

diff --git a/scripts/format.sh b/scripts/format.sh
index daf6fd988ba..4d504f98c03 100755
--- a/scripts/format.sh
+++ b/scripts/format.sh
@@ -8,7 +8,7 @@ echo Formatting OCaml code...
 opam exec -- dune build @fmt --auto-promote
 
 echo Formatting ReScript code...
-files=$(find packages tests -type f \( -name "*.res" -o -name "*.resi" \) ! -name "syntaxErrors*" ! -name "generated_mocha_test.res" ! -path "tests/build_tests/super_errors/fixtures/break_keyword_binding.res" ! -path "tests/syntax_tests*" ! -path "tests/analysis_tests/tests*" ! -path "*/node_modules/*")
+files=$(find packages tests -type f \( -name "*.res" -o -name "*.resi" \) ! -name "syntaxErrors*" ! -name "generated_mocha_test.res" ! -path "tests/build_tests/super_errors/fixtures/break_keyword_binding.res" ! -path "tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/*" ! -path "tests/syntax_tests*" ! -path "tests/analysis_tests/tests*" ! -path "*/node_modules/*")
 ./cli/rescript.js format $files
 
 echo Formatting JS code...
diff --git a/scripts/format_check.sh b/scripts/format_check.sh
index 84edccf479e..b4a57d02c18 100755
--- a/scripts/format_check.sh
+++ b/scripts/format_check.sh
@@ -17,7 +17,7 @@ case "$(uname -s)" in
     fi
 
     echo "Checking ReScript code formatting..."
-    files=$(find packages tests -type f \( -name "*.res" -o -name "*.resi" \) ! -name "syntaxErrors*" ! -name "generated_mocha_test.res" ! -path "tests/build_tests/super_errors/fixtures/break_keyword_binding.res" ! -path "tests/syntax_tests*" ! -path "tests/analysis_tests/tests*" ! -path "*/node_modules/*")
+    files=$(find packages tests -type f \( -name "*.res" -o -name "*.resi" \) ! -name "syntaxErrors*" ! -name "generated_mocha_test.res" ! -path "tests/build_tests/super_errors/fixtures/break_keyword_binding.res" ! -path "tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/*" ! -path "tests/syntax_tests*" ! -path "tests/analysis_tests/tests*" ! -path "*/node_modules/*")
     if ./cli/rescript.js format --check $files; then
       printf "${successGreen}✅ ReScript code formatting ok.${reset}\n"
     else
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_not_compiled.expected b/tests/build_tests/super_errors_multi/expected/Iface_not_compiled.expected
new file mode 100644
index 00000000000..9075954a615
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_not_compiled.expected
@@ -0,0 +1,18 @@
+===== Foo.resi =====
+
+  Syntax error!
+  /.../fixtures/Iface_not_compiled/Foo.resi:1:12
+
+  1 │ let v: int =
+  2 │ 
+
+  I'm not sure what to parse here when looking at "=".
+
+
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_not_compiled/Foo.res
+
+  Could not find the .cmi file for interface
+  /.../fixtures/Iface_not_compiled/Foo.resi.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/Foo.res
new file mode 100644
index 00000000000..ab49c6303bd
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/Foo.res
@@ -0,0 +1 @@
+let v = 1
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/Foo.resi
new file mode 100644
index 00000000000..bc6599a137c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_not_compiled/Foo.resi
@@ -0,0 +1 @@
+let v: int =

From 41c388f07d1aa4239b8328e672cf84ad3ec5a1bc Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 10:10:26 +0200
Subject: [PATCH 08/16] super_errors_multi: cover cross-module exception,
 record extra field, polyvariant constraint, alias dot access

---
 .../Cross_exception_arity_mismatch.expected      |  9 +++++++++
 .../Cross_module_alias_dot_access.expected       | 11 +++++++++++
 .../Cross_polyvariant_constraint.expected        | 16 ++++++++++++++++
 .../expected/Cross_record_extra_field.expected   | 11 +++++++++++
 .../Cross_exception_arity_mismatch/Errors.res    |  1 +
 .../Cross_exception_arity_mismatch/User.res      |  1 +
 .../Cross_module_alias_dot_access/Lib.res        |  3 +++
 .../Cross_module_alias_dot_access/User.res       |  3 +++
 .../Cross_polyvariant_constraint/Spec.res        |  8 ++++++++
 .../Cross_polyvariant_constraint/User.res        |  1 +
 .../fixtures/Cross_record_extra_field/Defs.res   |  1 +
 .../fixtures/Cross_record_extra_field/User.res   |  1 +
 12 files changed, 66 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_exception_arity_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_module_alias_dot_access.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_polyvariant_constraint.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_record_extra_field.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_exception_arity_mismatch/Errors.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_exception_arity_mismatch/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_module_alias_dot_access/Lib.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_module_alias_dot_access/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_polyvariant_constraint/Spec.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_polyvariant_constraint/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_record_extra_field/Defs.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_record_extra_field/User.res

diff --git a/tests/build_tests/super_errors_multi/expected/Cross_exception_arity_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Cross_exception_arity_mismatch.expected
new file mode 100644
index 00000000000..5f6cc2ef6c2
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_exception_arity_mismatch.expected
@@ -0,0 +1,9 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_exception_arity_mismatch/User.res:1:28-52
+
+  1 │ let raise_it = () => throw(Errors.ParseError("oops"))
+  2 │ 
+
+  This variant constructor Errors.ParseError expects 2 arguments, but it's only being passed 1.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_module_alias_dot_access.expected b/tests/build_tests/super_errors_multi/expected/Cross_module_alias_dot_access.expected
new file mode 100644
index 00000000000..d4e1595922d
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_module_alias_dot_access.expected
@@ -0,0 +1,11 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_module_alias_dot_access/User.res:3:21-26
+
+  1 │ module S = Lib.Settings
+  2 │ 
+  3 │ let port = S.port + S.host
+  4 │ 
+
+  The value host can't be found in S
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_polyvariant_constraint.expected b/tests/build_tests/super_errors_multi/expected/Cross_polyvariant_constraint.expected
new file mode 100644
index 00000000000..c3ddd670262
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_polyvariant_constraint.expected
@@ -0,0 +1,16 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_polyvariant_constraint/User.res:1:19-25
+
+  1 │ let v = Spec.pick(#Purple)
+  2 │ 
+
+  This has type: [> #Purple]
+  But this function argument is expecting: Spec.allowed
+  
+  The second polymorphic variant is closed and doesn't include the constructor: #Purple.
+  
+  Possible solutions:
+  - Either make the second variant open so it can accept additional constructors. To do this, make sure the type starts with [> instead of [
+  - Or add the missing constructor to it.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_record_extra_field.expected b/tests/build_tests/super_errors_multi/expected/Cross_record_extra_field.expected
new file mode 100644
index 00000000000..6c1d5026207
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_record_extra_field.expected
@@ -0,0 +1,11 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_record_extra_field/User.res:1:30-34
+
+  1 │ let r: Defs.t = {a: 1, b: 2, extra: 3}
+  2 │ 
+
+  The field extra does not belong to type Defs.t
+  
+  This record expression is expected to have type Defs.t
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_exception_arity_mismatch/Errors.res b/tests/build_tests/super_errors_multi/fixtures/Cross_exception_arity_mismatch/Errors.res
new file mode 100644
index 00000000000..cb0fb172ac3
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_exception_arity_mismatch/Errors.res
@@ -0,0 +1 @@
+exception ParseError(string, int)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_exception_arity_mismatch/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_exception_arity_mismatch/User.res
new file mode 100644
index 00000000000..6b4c1a84781
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_exception_arity_mismatch/User.res
@@ -0,0 +1 @@
+let raise_it = () => throw(Errors.ParseError("oops"))
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_module_alias_dot_access/Lib.res b/tests/build_tests/super_errors_multi/fixtures/Cross_module_alias_dot_access/Lib.res
new file mode 100644
index 00000000000..b98d30ce23c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_module_alias_dot_access/Lib.res
@@ -0,0 +1,3 @@
+module Settings = {
+  let port = 8080
+}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_module_alias_dot_access/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_module_alias_dot_access/User.res
new file mode 100644
index 00000000000..4a51ad4526c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_module_alias_dot_access/User.res
@@ -0,0 +1,3 @@
+module S = Lib.Settings
+
+let port = S.port + S.host
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_polyvariant_constraint/Spec.res b/tests/build_tests/super_errors_multi/fixtures/Cross_polyvariant_constraint/Spec.res
new file mode 100644
index 00000000000..a660efb87bd
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_polyvariant_constraint/Spec.res
@@ -0,0 +1,8 @@
+type allowed = [#Red | #Green | #Blue]
+
+let pick: allowed => string = c =>
+  switch c {
+  | #Red => "r"
+  | #Green => "g"
+  | #Blue => "b"
+  }
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_polyvariant_constraint/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_polyvariant_constraint/User.res
new file mode 100644
index 00000000000..5e3385d240a
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_polyvariant_constraint/User.res
@@ -0,0 +1 @@
+let v = Spec.pick(#Purple)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_record_extra_field/Defs.res b/tests/build_tests/super_errors_multi/fixtures/Cross_record_extra_field/Defs.res
new file mode 100644
index 00000000000..e2e17af7455
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_record_extra_field/Defs.res
@@ -0,0 +1 @@
+type t = {a: int, b: int}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_record_extra_field/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_record_extra_field/User.res
new file mode 100644
index 00000000000..6073586019d
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_record_extra_field/User.res
@@ -0,0 +1 @@
+let r: Defs.t = {a: 1, b: 2, extra: 3}

From 441fd51ebf7a50f4442ee22f988ccc815fbdc50e Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 10:26:41 +0200
Subject: [PATCH 09/16] super_errors_multi: cover inline record constructor,
 variant spread, async/promise, optional label omitted

---
 .../expected/Cross_async_promise_mismatch.expected | 12 ++++++++++++
 .../Cross_inline_record_constructor.expected       |  9 +++++++++
 .../expected/Cross_optional_label_omitted.expected | 14 ++++++++++++++
 .../expected/Cross_variant_spread.expected         | 13 +++++++++++++
 .../fixtures/Cross_async_promise_mismatch/Lib.res  |  1 +
 .../fixtures/Cross_async_promise_mismatch/User.res |  1 +
 .../Cross_inline_record_constructor/Defs.res       |  1 +
 .../Cross_inline_record_constructor/User.res       |  1 +
 .../fixtures/Cross_optional_label_omitted/Lib.res  |  1 +
 .../fixtures/Cross_optional_label_omitted/User.res |  1 +
 .../fixtures/Cross_variant_spread/Base.res         |  3 +++
 .../fixtures/Cross_variant_spread/Ext.res          |  4 ++++
 12 files changed, 61 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_async_promise_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_inline_record_constructor.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_optional_label_omitted.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_variant_spread.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_async_promise_mismatch/Lib.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_async_promise_mismatch/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_inline_record_constructor/Defs.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_inline_record_constructor/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_optional_label_omitted/Lib.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_optional_label_omitted/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_variant_spread/Base.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_variant_spread/Ext.res

diff --git a/tests/build_tests/super_errors_multi/expected/Cross_async_promise_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Cross_async_promise_mismatch.expected
new file mode 100644
index 00000000000..3f1fdb107db
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_async_promise_mismatch.expected
@@ -0,0 +1,12 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_async_promise_mismatch/User.res:1:29-44
+
+  1 │ let consume = (): string => Lib.fetch("api")
+  2 │ 
+
+  This has type: promise<string>
+  But it's expected to have type: string
+
+  - Did you mean to await this promise before using it?
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_inline_record_constructor.expected b/tests/build_tests/super_errors_multi/expected/Cross_inline_record_constructor.expected
new file mode 100644
index 00000000000..6a1cdb1ef84
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_inline_record_constructor.expected
@@ -0,0 +1,9 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_inline_record_constructor/User.res:1:9-23
+
+  1 │ let v = Defs.Pair(1, 2)
+  2 │ 
+
+  This constructor expects an inlined record argument.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_optional_label_omitted.expected b/tests/build_tests/super_errors_multi/expected/Cross_optional_label_omitted.expected
new file mode 100644
index 00000000000..8fd5d7769c9
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_optional_label_omitted.expected
@@ -0,0 +1,14 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_optional_label_omitted/User.res:1:9-17
+
+  1 │ let s = Lib.greet()
+  2 │ 
+
+  This function call is incorrect.
+  The function has type:
+  (~name: string, ~greeting: string=?, unit) => string
+  
+  - Missing arguments that must be provided: ~name
+  - Hint: Did you want to partially apply the function? You can do that by putting `...` just before the closing parens of the function call. Example: yourFn(~arg1=someVar, ...)
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_variant_spread.expected b/tests/build_tests/super_errors_multi/expected/Cross_variant_spread.expected
new file mode 100644
index 00000000000..8647cc95297
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_variant_spread.expected
@@ -0,0 +1,13 @@
+===== Ext.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_variant_spread/Ext.res:3:8-13
+
+  1 │ type t =
+  2 │   | A
+  3 │   | ...Base.t
+  4 │   | C
+  5 │ 
+
+  Variant Base.t has a constructor named A, but a constructor named A already exists in the variant it's spread into.
+  You cannot spread variants with overlapping constructors.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_async_promise_mismatch/Lib.res b/tests/build_tests/super_errors_multi/fixtures/Cross_async_promise_mismatch/Lib.res
new file mode 100644
index 00000000000..525fdfb21c7
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_async_promise_mismatch/Lib.res
@@ -0,0 +1 @@
+let fetch = async (url: string): string => url
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_async_promise_mismatch/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_async_promise_mismatch/User.res
new file mode 100644
index 00000000000..992915231d7
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_async_promise_mismatch/User.res
@@ -0,0 +1 @@
+let consume = (): string => Lib.fetch("api")
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_inline_record_constructor/Defs.res b/tests/build_tests/super_errors_multi/fixtures/Cross_inline_record_constructor/Defs.res
new file mode 100644
index 00000000000..164c83aab30
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_inline_record_constructor/Defs.res
@@ -0,0 +1 @@
+type t = Pair({x: int, y: int})
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_inline_record_constructor/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_inline_record_constructor/User.res
new file mode 100644
index 00000000000..f08bcf4eb22
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_inline_record_constructor/User.res
@@ -0,0 +1 @@
+let v = Defs.Pair(1, 2)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_optional_label_omitted/Lib.res b/tests/build_tests/super_errors_multi/fixtures/Cross_optional_label_omitted/Lib.res
new file mode 100644
index 00000000000..9234f71d1e7
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_optional_label_omitted/Lib.res
@@ -0,0 +1 @@
+let greet = (~name: string, ~greeting: string="Hello", ()) => greeting ++ ", " ++ name
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_optional_label_omitted/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_optional_label_omitted/User.res
new file mode 100644
index 00000000000..562299106da
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_optional_label_omitted/User.res
@@ -0,0 +1 @@
+let s = Lib.greet()
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_variant_spread/Base.res b/tests/build_tests/super_errors_multi/fixtures/Cross_variant_spread/Base.res
new file mode 100644
index 00000000000..ebf3f1e2d83
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_variant_spread/Base.res
@@ -0,0 +1,3 @@
+type t =
+  | A
+  | B
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_variant_spread/Ext.res b/tests/build_tests/super_errors_multi/fixtures/Cross_variant_spread/Ext.res
new file mode 100644
index 00000000000..cf5cb8c0580
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_variant_spread/Ext.res
@@ -0,0 +1,4 @@
+type t =
+  | A
+  | ...Base.t
+  | C

From 9fc9698ddfcaac8cf2d3d799cdc48539287efea8 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 10:33:20 +0200
Subject: [PATCH 10/16] super_errors_multi: cover interface-hidden record
 access, uncurried arity, dict pattern, .resi-only ref

---
 .../expected/Cross_dict_pattern.expected        | 13 +++++++++++++
 .../Cross_hidden_through_interface.expected     | 17 +++++++++++++++++
 .../Cross_module_type_only_no_impl.expected     | 12 ++++++++++++
 .../expected/Cross_uncurried_arity.expected     |  9 +++++++++
 .../fixtures/Cross_dict_pattern/Defs.res        |  1 +
 .../fixtures/Cross_dict_pattern/User.res        |  4 ++++
 .../Cross_hidden_through_interface/Defs.res     |  3 +++
 .../Cross_hidden_through_interface/Defs.resi    |  3 +++
 .../Cross_hidden_through_interface/User.res     |  2 ++
 .../Cross_module_type_only_no_impl/Iface.resi   |  1 +
 .../Cross_module_type_only_no_impl/User.res     |  1 +
 .../fixtures/Cross_uncurried_arity/Lib.res      |  1 +
 .../fixtures/Cross_uncurried_arity/User.res     |  1 +
 13 files changed, 68 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_dict_pattern.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_hidden_through_interface.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_module_type_only_no_impl.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_uncurried_arity.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_dict_pattern/Defs.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_dict_pattern/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/Defs.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/Defs.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_module_type_only_no_impl/Iface.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_module_type_only_no_impl/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_uncurried_arity/Lib.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_uncurried_arity/User.res

diff --git a/tests/build_tests/super_errors_multi/expected/Cross_dict_pattern.expected b/tests/build_tests/super_errors_multi/expected/Cross_dict_pattern.expected
new file mode 100644
index 00000000000..0350dffa209
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_dict_pattern.expected
@@ -0,0 +1,13 @@
+===== User.res =====
+
+  Warning number 8
+  /.../fixtures/Cross_dict_pattern/User.res:2:3-4:3
+
+  1 │ let read = (cfg: Defs.config) =>
+  2 │   switch cfg {
+  3 │   | dict{"port": p} => p
+  4 │   }
+  5 │ 
+
+  You forgot to handle a possible case here, for example: 
+  | {port: ?None}
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_hidden_through_interface.expected b/tests/build_tests/super_errors_multi/expected/Cross_hidden_through_interface.expected
new file mode 100644
index 00000000000..bf099d37301
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_hidden_through_interface.expected
@@ -0,0 +1,17 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_hidden_through_interface/User.res:2:16
+
+  1 │ let v = Defs.make()
+  2 │ let leaked = v.x
+  3 │ 
+
+  You're trying to access the record field x, but the thing you're trying to access it on is not a record. 
+  
+The type of the thing you're trying to access it on is:
+  
+Defs.t
+  
+
+  Only records have fields that can be accessed with dot notation.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_module_type_only_no_impl.expected b/tests/build_tests/super_errors_multi/expected/Cross_module_type_only_no_impl.expected
new file mode 100644
index 00000000000..3ef0fee69df
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_module_type_only_no_impl.expected
@@ -0,0 +1,12 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_module_type_only_no_impl/User.res:1:17-23
+
+  1 │ let x: string = Iface.v
+  2 │ 
+
+  This has type: int
+  But it's expected to have type: string
+  
+  You can convert int to string with Int.toString.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Cross_uncurried_arity.expected b/tests/build_tests/super_errors_multi/expected/Cross_uncurried_arity.expected
new file mode 100644
index 00000000000..a229159ea58
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_uncurried_arity.expected
@@ -0,0 +1,9 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_uncurried_arity/User.res:1:23-29
+
+  1 │ let bad: int => int = Lib.add
+  2 │ 
+
+  This function is expected to have 1 argument, but has 3
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_dict_pattern/Defs.res b/tests/build_tests/super_errors_multi/fixtures/Cross_dict_pattern/Defs.res
new file mode 100644
index 00000000000..ad12bd18137
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_dict_pattern/Defs.res
@@ -0,0 +1 @@
+type config = dict<int>
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_dict_pattern/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_dict_pattern/User.res
new file mode 100644
index 00000000000..1782881539c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_dict_pattern/User.res
@@ -0,0 +1,4 @@
+let read = (cfg: Defs.config) =>
+  switch cfg {
+  | dict{"port": p} => p
+  }
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/Defs.res b/tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/Defs.res
new file mode 100644
index 00000000000..abb7607f0e8
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/Defs.res
@@ -0,0 +1,3 @@
+type t = {x: int, y: int}
+
+let make = () => {x: 0, y: 0}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/Defs.resi b/tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/Defs.resi
new file mode 100644
index 00000000000..f856ba275af
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/Defs.resi
@@ -0,0 +1,3 @@
+type t
+
+let make: unit => t
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/User.res
new file mode 100644
index 00000000000..3beb6cc8c57
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_hidden_through_interface/User.res
@@ -0,0 +1,2 @@
+let v = Defs.make()
+let leaked = v.x
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_module_type_only_no_impl/Iface.resi b/tests/build_tests/super_errors_multi/fixtures/Cross_module_type_only_no_impl/Iface.resi
new file mode 100644
index 00000000000..19b83dc216f
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_module_type_only_no_impl/Iface.resi
@@ -0,0 +1 @@
+let v: int
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_module_type_only_no_impl/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_module_type_only_no_impl/User.res
new file mode 100644
index 00000000000..adc242ff65e
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_module_type_only_no_impl/User.res
@@ -0,0 +1 @@
+let x: string = Iface.v
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_uncurried_arity/Lib.res b/tests/build_tests/super_errors_multi/fixtures/Cross_uncurried_arity/Lib.res
new file mode 100644
index 00000000000..20528a0755c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_uncurried_arity/Lib.res
@@ -0,0 +1 @@
+let add = (a: int, b: int, c: int) => a + b + c
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_uncurried_arity/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_uncurried_arity/User.res
new file mode 100644
index 00000000000..22c26b76f30
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_uncurried_arity/User.res
@@ -0,0 +1 @@
+let bad: int => int = Lib.add

From e504fee8bd6f6600c5c3e232c4175cb40a22bea0 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 10:35:34 +0200
Subject: [PATCH 11/16] super_errors_multi: cover typecore
 Unqualified_gadt_pattern via cross-module GADT disambiguation

---
 .../expected/Cross_gadt_pattern.expected             | 12 ++++++++++++
 .../fixtures/Cross_gadt_pattern/Gadt.res             |  3 +++
 .../fixtures/Cross_gadt_pattern/User.res             |  5 +++++
 3 files changed, 20 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Cross_gadt_pattern.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_gadt_pattern/Gadt.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Cross_gadt_pattern/User.res

diff --git a/tests/build_tests/super_errors_multi/expected/Cross_gadt_pattern.expected b/tests/build_tests/super_errors_multi/expected/Cross_gadt_pattern.expected
new file mode 100644
index 00000000000..7222bfb318d
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Cross_gadt_pattern.expected
@@ -0,0 +1,12 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Cross_gadt_pattern/User.res:3:5-7
+
+  1 │ let bad: Gadt.t<int> => string = x =>
+  2 │   switch x {
+  3 │   | Int(n) => n
+  4 │   | Pair(_, _) => "pair"
+  5 │   }
+
+  The GADT constructor Int of type Gadt.t must be qualified in this pattern.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_gadt_pattern/Gadt.res b/tests/build_tests/super_errors_multi/fixtures/Cross_gadt_pattern/Gadt.res
new file mode 100644
index 00000000000..7e78cb17ed1
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_gadt_pattern/Gadt.res
@@ -0,0 +1,3 @@
+type rec t<_> =
+  | Int(int): t<int>
+  | Pair(t<'a>, t<'b>): t<('a, 'b)>
diff --git a/tests/build_tests/super_errors_multi/fixtures/Cross_gadt_pattern/User.res b/tests/build_tests/super_errors_multi/fixtures/Cross_gadt_pattern/User.res
new file mode 100644
index 00000000000..7081757e9b2
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Cross_gadt_pattern/User.res
@@ -0,0 +1,5 @@
+let bad: Gadt.t<int> => string = x =>
+  switch x {
+  | Int(n) => n
+  | Pair(_, _) => "pair"
+  }

From 024707ca5e2c905e7714188a9c145adf5af6e678 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 10:42:12 +0200
Subject: [PATCH 12/16] super_errors_multi: cover typecore Modules_not_allowed
 and Unexpected_existential

---
 .../expected/Modules_not_allowed_toplevel.expected    | 11 +++++++++++
 .../expected/Unexpected_existential_in_let.expected   | 11 +++++++++++
 .../fixtures/Modules_not_allowed_toplevel/Sig.res     |  3 +++
 .../fixtures/Modules_not_allowed_toplevel/User.res    |  8 ++++++++
 .../fixtures/Unexpected_existential_in_let/Gadt.res   |  1 +
 .../fixtures/Unexpected_existential_in_let/User.res   |  3 +++
 6 files changed, 37 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Modules_not_allowed_toplevel.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Unexpected_existential_in_let.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Modules_not_allowed_toplevel/Sig.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Modules_not_allowed_toplevel/User.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Unexpected_existential_in_let/Gadt.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Unexpected_existential_in_let/User.res

diff --git a/tests/build_tests/super_errors_multi/expected/Modules_not_allowed_toplevel.expected b/tests/build_tests/super_errors_multi/expected/Modules_not_allowed_toplevel.expected
new file mode 100644
index 00000000000..7bbe7fbdc74
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Modules_not_allowed_toplevel.expected
@@ -0,0 +1,11 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Modules_not_allowed_toplevel/User.res:8:5-13
+
+  6 │   )
+  7 │ 
+  8 │ let module(M) = make()
+  9 │ 
+
+  Modules are not allowed in this pattern.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Unexpected_existential_in_let.expected b/tests/build_tests/super_errors_multi/expected/Unexpected_existential_in_let.expected
new file mode 100644
index 00000000000..719a57ea4ad
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Unexpected_existential_in_let.expected
@@ -0,0 +1,11 @@
+===== User.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Unexpected_existential_in_let/User.res:3:5-17
+
+  1 │ let value: Gadt.wrap<unit> = Gadt.Pack(1)
+  2 │ 
+  3 │ let Gadt.Pack(_x) = value
+  4 │ 
+
+  Unexpected existential
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Modules_not_allowed_toplevel/Sig.res b/tests/build_tests/super_errors_multi/fixtures/Modules_not_allowed_toplevel/Sig.res
new file mode 100644
index 00000000000..fff5b5fd01a
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Modules_not_allowed_toplevel/Sig.res
@@ -0,0 +1,3 @@
+module type S = {
+  let v: int
+}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Modules_not_allowed_toplevel/User.res b/tests/build_tests/super_errors_multi/fixtures/Modules_not_allowed_toplevel/User.res
new file mode 100644
index 00000000000..fe841b594ff
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Modules_not_allowed_toplevel/User.res
@@ -0,0 +1,8 @@
+let make = (): module(Sig.S) =>
+  module(
+    {
+      let v = 1
+    }
+  )
+
+let module(M) = make()
diff --git a/tests/build_tests/super_errors_multi/fixtures/Unexpected_existential_in_let/Gadt.res b/tests/build_tests/super_errors_multi/fixtures/Unexpected_existential_in_let/Gadt.res
new file mode 100644
index 00000000000..38495779cdb
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Unexpected_existential_in_let/Gadt.res
@@ -0,0 +1 @@
+type rec wrap<_> = Pack('a): wrap<unit>
diff --git a/tests/build_tests/super_errors_multi/fixtures/Unexpected_existential_in_let/User.res b/tests/build_tests/super_errors_multi/fixtures/Unexpected_existential_in_let/User.res
new file mode 100644
index 00000000000..bf843b2a868
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Unexpected_existential_in_let/User.res
@@ -0,0 +1,3 @@
+let value: Gadt.wrap<unit> = Gadt.Pack(1)
+
+let Gadt.Pack(_x) = value

From fec7103f5bee42a53dfc3e3e08e4a75b5e9deb2f Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 10:52:18 +0200
Subject: [PATCH 13/16] super_errors_multi: cover includecore Privacy,
 Field_mutable, Field_optional, Unboxed_representation, Tag_name mismatches

---
 .../Iface_field_mutable_mismatch.expected     | 19 ++++++++++++++++
 .../Iface_field_optional_mismatch.expected    | 19 ++++++++++++++++
 .../expected/Iface_privacy_mismatch.expected  | 19 ++++++++++++++++
 .../expected/Iface_tag_name_mismatch.expected | 22 +++++++++++++++++++
 .../Iface_unboxed_variant_mismatch.expected   | 21 ++++++++++++++++++
 .../Iface_field_mutable_mismatch/Foo.res      |  1 +
 .../Iface_field_mutable_mismatch/Foo.resi     |  1 +
 .../Iface_field_optional_mismatch/Foo.res     |  1 +
 .../Iface_field_optional_mismatch/Foo.resi    |  1 +
 .../fixtures/Iface_privacy_mismatch/Foo.res   |  1 +
 .../fixtures/Iface_privacy_mismatch/Foo.resi  |  1 +
 .../fixtures/Iface_tag_name_mismatch/Foo.res  |  4 ++++
 .../fixtures/Iface_tag_name_mismatch/Foo.resi |  4 ++++
 .../Iface_unboxed_variant_mismatch/Foo.res    |  1 +
 .../Iface_unboxed_variant_mismatch/Foo.resi   |  2 ++
 15 files changed, 117 insertions(+)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_field_mutable_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_field_optional_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_privacy_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_tag_name_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_unboxed_variant_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_field_mutable_mismatch/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_field_mutable_mismatch/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_field_optional_mismatch/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_field_optional_mismatch/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_privacy_mismatch/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_privacy_mismatch/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_tag_name_mismatch/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_tag_name_mismatch/Foo.resi
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_unboxed_variant_mismatch/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_unboxed_variant_mismatch/Foo.resi

diff --git a/tests/build_tests/super_errors_multi/expected/Iface_field_mutable_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Iface_field_mutable_mismatch.expected
new file mode 100644
index 00000000000..1b0534cb661
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_field_mutable_mismatch.expected
@@ -0,0 +1,19 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_field_mutable_mismatch/Foo.res:1:1-21
+
+  1 │ type t = {count: int}
+  2 │ 
+
+  The implementation /.../fixtures/Iface_field_mutable_mismatch/Foo.res
+  does not match the interface /.../fixtures/Iface_field_mutable_mismatch/foo.cmi:
+  Type declarations do not match:
+    type t = {count: int}
+  is not included in
+    type t = {mutable count: int}
+  /.../fixtures/Iface_field_mutable_mismatch/Foo.resi:1:1-29:
+    Expected declaration
+  /.../fixtures/Iface_field_mutable_mismatch/Foo.res:1:1-21:
+    Actual declaration
+  The mutability of field count is different.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_field_optional_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Iface_field_optional_mismatch.expected
new file mode 100644
index 00000000000..56261f1f0fa
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_field_optional_mismatch.expected
@@ -0,0 +1,19 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_field_optional_mismatch/Foo.res:1:1-28
+
+  1 │ type t = {a: int, b: string}
+  2 │ 
+
+  The implementation /.../fixtures/Iface_field_optional_mismatch/Foo.res
+  does not match the interface /.../fixtures/Iface_field_optional_mismatch/foo.cmi:
+  Type declarations do not match:
+    type t = {a: int, b: string}
+  is not included in
+    type t = {a: int, b?: string}
+  /.../fixtures/Iface_field_optional_mismatch/Foo.resi:1:1-29:
+    Expected declaration
+  /.../fixtures/Iface_field_optional_mismatch/Foo.res:1:1-28:
+    Actual declaration
+  The optional attribute of field b is different.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_privacy_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Iface_privacy_mismatch.expected
new file mode 100644
index 00000000000..621a81f6eca
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_privacy_mismatch.expected
@@ -0,0 +1,19 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_privacy_mismatch/Foo.res:1:1-20
+
+  1 │ type t = private int
+  2 │ 
+
+  The implementation /.../fixtures/Iface_privacy_mismatch/Foo.res
+  does not match the interface /.../fixtures/Iface_privacy_mismatch/foo.cmi:
+  Type declarations do not match:
+    type t = int
+  is not included in
+    type t = int
+  /.../fixtures/Iface_privacy_mismatch/Foo.resi:1:1-12:
+    Expected declaration
+  /.../fixtures/Iface_privacy_mismatch/Foo.res:1:1-20:
+    Actual declaration
+  A private type would be revealed.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_tag_name_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Iface_tag_name_mismatch.expected
new file mode 100644
index 00000000000..96795bfb816
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_tag_name_mismatch.expected
@@ -0,0 +1,22 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_tag_name_mismatch/Foo.res:2:1-4:5
+
+  1 │ @tag("type")
+  2 │ type t =
+  3 │   | @as("a") A
+  4 │   | B
+  5 │ 
+
+  The implementation /.../fixtures/Iface_tag_name_mismatch/Foo.res
+  does not match the interface /.../fixtures/Iface_tag_name_mismatch/foo.cmi:
+  Type declarations do not match:
+    type t = @as("a") A | B
+  is not included in
+    type t = @as("a") A | B
+  /.../fixtures/Iface_tag_name_mismatch/Foo.resi:2:1-4:5:
+    Expected declaration
+  /.../fixtures/Iface_tag_name_mismatch/Foo.res:2:1-4:5:
+    Actual declaration
+  Their @tag annotations differ.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_unboxed_variant_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Iface_unboxed_variant_mismatch.expected
new file mode 100644
index 00000000000..dc867992b77
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_unboxed_variant_mismatch.expected
@@ -0,0 +1,21 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_unboxed_variant_mismatch/Foo.res:1:1-2:13
+
+  1 │ type t =
+  2 │   | Wrap(int)
+  3 │ 
+
+  The implementation /.../fixtures/Iface_unboxed_variant_mismatch/Foo.res
+  does not match the interface /.../fixtures/Iface_unboxed_variant_mismatch/foo.cmi:
+  Type declarations do not match:
+    type t = Wrap(int)
+  is not included in
+    @unboxed type t = Wrap(int)
+  /.../fixtures/Iface_unboxed_variant_mismatch/Foo.resi:2:1-3:13:
+    Expected declaration
+  /.../fixtures/Iface_unboxed_variant_mismatch/Foo.res:1:1-2:13:
+    Actual declaration
+  Their internal representations differ:
+  the second declaration uses unboxed representation.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_field_mutable_mismatch/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_field_mutable_mismatch/Foo.res
new file mode 100644
index 00000000000..eddf68bf0e3
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_field_mutable_mismatch/Foo.res
@@ -0,0 +1 @@
+type t = {count: int}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_field_mutable_mismatch/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_field_mutable_mismatch/Foo.resi
new file mode 100644
index 00000000000..329fbfd10e2
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_field_mutable_mismatch/Foo.resi
@@ -0,0 +1 @@
+type t = {mutable count: int}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_field_optional_mismatch/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_field_optional_mismatch/Foo.res
new file mode 100644
index 00000000000..ff122aa325e
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_field_optional_mismatch/Foo.res
@@ -0,0 +1 @@
+type t = {a: int, b: string}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_field_optional_mismatch/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_field_optional_mismatch/Foo.resi
new file mode 100644
index 00000000000..fae28d73846
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_field_optional_mismatch/Foo.resi
@@ -0,0 +1 @@
+type t = {a: int, b?: string}
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_privacy_mismatch/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_privacy_mismatch/Foo.res
new file mode 100644
index 00000000000..0d8eb0e6321
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_privacy_mismatch/Foo.res
@@ -0,0 +1 @@
+type t = private int
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_privacy_mismatch/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_privacy_mismatch/Foo.resi
new file mode 100644
index 00000000000..975adb5316a
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_privacy_mismatch/Foo.resi
@@ -0,0 +1 @@
+type t = int
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_tag_name_mismatch/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_tag_name_mismatch/Foo.res
new file mode 100644
index 00000000000..6bbd0febeac
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_tag_name_mismatch/Foo.res
@@ -0,0 +1,4 @@
+@tag("type")
+type t =
+  | @as("a") A
+  | B
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_tag_name_mismatch/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_tag_name_mismatch/Foo.resi
new file mode 100644
index 00000000000..b0b2699b87c
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_tag_name_mismatch/Foo.resi
@@ -0,0 +1,4 @@
+@tag("kind")
+type t =
+  | @as("a") A
+  | B
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_unboxed_variant_mismatch/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_unboxed_variant_mismatch/Foo.res
new file mode 100644
index 00000000000..519e92579c8
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_unboxed_variant_mismatch/Foo.res
@@ -0,0 +1 @@
+type t = Wrap(int)
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_unboxed_variant_mismatch/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_unboxed_variant_mismatch/Foo.resi
new file mode 100644
index 00000000000..5b198abe28f
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_unboxed_variant_mismatch/Foo.resi
@@ -0,0 +1,2 @@
+@unboxed
+type t = Wrap(int)

From 24cef595026835dc343cdffc201a44d39239c46c Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 10:57:29 +0200
Subject: [PATCH 14/16] super_errors_multi: cover includecore
 Variant_representation via different @as tag types

---
 .../Iface_unboxed_variant_mismatch.expected   | 11 +++++-----
 ...e_variant_representation_mismatch.expected | 21 +++++++++++++++++++
 .../Foo.res                                   |  3 +++
 .../Foo.resi                                  |  3 +++
 4 files changed, 32 insertions(+), 6 deletions(-)
 create mode 100644 tests/build_tests/super_errors_multi/expected/Iface_variant_representation_mismatch.expected
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_variant_representation_mismatch/Foo.res
 create mode 100644 tests/build_tests/super_errors_multi/fixtures/Iface_variant_representation_mismatch/Foo.resi

diff --git a/tests/build_tests/super_errors_multi/expected/Iface_unboxed_variant_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Iface_unboxed_variant_mismatch.expected
index dc867992b77..3d6d2f2df17 100644
--- a/tests/build_tests/super_errors_multi/expected/Iface_unboxed_variant_mismatch.expected
+++ b/tests/build_tests/super_errors_multi/expected/Iface_unboxed_variant_mismatch.expected
@@ -1,11 +1,10 @@
 ===== Foo.res =====
 
   We've found a bug for you!
-  /.../fixtures/Iface_unboxed_variant_mismatch/Foo.res:1:1-2:13
+  /.../fixtures/Iface_unboxed_variant_mismatch/Foo.res:1:1-18
 
-  1 │ type t =
-  2 │   | Wrap(int)
-  3 │ 
+  1 │ type t = Wrap(int)
+  2 │ 
 
   The implementation /.../fixtures/Iface_unboxed_variant_mismatch/Foo.res
   does not match the interface /.../fixtures/Iface_unboxed_variant_mismatch/foo.cmi:
@@ -13,9 +12,9 @@
     type t = Wrap(int)
   is not included in
     @unboxed type t = Wrap(int)
-  /.../fixtures/Iface_unboxed_variant_mismatch/Foo.resi:2:1-3:13:
+  /.../fixtures/Iface_unboxed_variant_mismatch/Foo.resi:2:1-18:
     Expected declaration
-  /.../fixtures/Iface_unboxed_variant_mismatch/Foo.res:1:1-2:13:
+  /.../fixtures/Iface_unboxed_variant_mismatch/Foo.res:1:1-18:
     Actual declaration
   Their internal representations differ:
   the second declaration uses unboxed representation.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/expected/Iface_variant_representation_mismatch.expected b/tests/build_tests/super_errors_multi/expected/Iface_variant_representation_mismatch.expected
new file mode 100644
index 00000000000..a9e569f984b
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/expected/Iface_variant_representation_mismatch.expected
@@ -0,0 +1,21 @@
+===== Foo.res =====
+
+  We've found a bug for you!
+  /.../fixtures/Iface_variant_representation_mismatch/Foo.res:1:1-3:5
+
+  1 │ type t =
+  2 │   | @as(0) A
+  3 │   | B
+  4 │ 
+
+  The implementation /.../fixtures/Iface_variant_representation_mismatch/Foo.res
+  does not match the interface /.../fixtures/Iface_variant_representation_mismatch/foo.cmi:
+  Type declarations do not match:
+    type t = @as(0) A | B
+  is not included in
+    type t = @as("zero") A | B
+  /.../fixtures/Iface_variant_representation_mismatch/Foo.resi:1:1-3:5:
+    Expected declaration
+  /.../fixtures/Iface_variant_representation_mismatch/Foo.res:1:1-3:5:
+    Actual declaration
+  The internal representations for case A are not equal.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_variant_representation_mismatch/Foo.res b/tests/build_tests/super_errors_multi/fixtures/Iface_variant_representation_mismatch/Foo.res
new file mode 100644
index 00000000000..82945d226e3
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_variant_representation_mismatch/Foo.res
@@ -0,0 +1,3 @@
+type t =
+  | @as(0) A
+  | B
diff --git a/tests/build_tests/super_errors_multi/fixtures/Iface_variant_representation_mismatch/Foo.resi b/tests/build_tests/super_errors_multi/fixtures/Iface_variant_representation_mismatch/Foo.resi
new file mode 100644
index 00000000000..4ef6252b611
--- /dev/null
+++ b/tests/build_tests/super_errors_multi/fixtures/Iface_variant_representation_mismatch/Foo.resi
@@ -0,0 +1,3 @@
+type t =
+  | @as("zero") A
+  | B

From 492fbcc503131680d5936f2167dd20fdc3777b71 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 18:09:30 +0200
Subject: [PATCH 15/16] Update changelog for #8433

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 85350be7e05..34d28f033b1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -47,6 +47,7 @@
 - Expand `super_errors` fixture coverage for warnings and errors. https://github.com/rescript-lang/rescript/pull/8429
 - Run `super_errors` fixtures in parallel (~2.4× faster locally). https://github.com/rescript-lang/rescript/pull/8430
 - Expand `super_errors` fixture coverage for the remaining reachable single-file error variants. https://github.com/rescript-lang/rescript/pull/8432
+- Add a multi-file fixture harness (`super_errors_multi`) for cross-module errors and warnings. https://github.com/rescript-lang/rescript/pull/8433
 
 
 # 13.0.0-alpha.4

From dcd0c8ecb616ed8d76dd3433780109497a8f8e80 Mon Sep 17 00:00:00 2001
From: Jono Prest <jjprest@gmail.com>
Date: Wed, 20 May 2026 18:20:54 +0200
Subject: [PATCH 16/16] super_errors_multi: lowercase `.cmi` basenames in
 snapshot post-processing

`find_in_path_uncap` resolves `.cmi` lookups case-insensitively, so the
filename printed in error messages picks up whichever case the host
filesystem returns: lowercase on macOS APFS/HFS+, capitalised on Linux
ext4. Snapshots captured locally on macOS therefore mismatch on Linux
CI (`foo.cmi` vs `Foo.cmi`).

Normalise every `.cmi` basename to lowercase in postProcessErrorOutput
so snapshots are platform-independent. The same function runs on the
expected file too, so existing snapshots keep matching.
---
 tests/build_tests/super_errors_multi/input.js | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tests/build_tests/super_errors_multi/input.js b/tests/build_tests/super_errors_multi/input.js
index 899f93170fb..b4a82ca4d21 100644
--- a/tests/build_tests/super_errors_multi/input.js
+++ b/tests/build_tests/super_errors_multi/input.js
@@ -47,6 +47,15 @@ function postProcessErrorOutput(fixtureName, output) {
     (_match, file) =>
       `/.../fixtures/${fixtureName}/${file.replace(/\\/g, "/")}`,
   );
+  // `find_in_path_uncap` resolves `.cmi` lookups case-insensitively, so the
+  // path printed in error messages picks up whichever case the host
+  // filesystem returns (lowercase on macOS APFS/HFS+, capitalised on Linux
+  // ext4). Normalise every `.cmi` basename to lowercase so snapshots are
+  // platform-independent.
+  result = result.replace(
+    /([^/\s]+)\.cmi\b/g,
+    (_, stem) => `${stem.toLowerCase()}.cmi`,
+  );
   return normalizeNewlines(result);
 }