From 381c01cdf06c23e871a9e4159aa275c097eea0b2 Mon Sep 17 00:00:00 2001
From: cs01 <cs01@users.noreply.github.com>
Date: Sun, 26 Apr 2026 11:50:48 -0700
Subject: [PATCH 1/2] [sema] reject inline as { ... } on opaque source types

---
 src/semantic/type-assertion-checker.ts      | 33 +++++++++++++++++++++
 tests/fixtures/errors/opaque-inline-cast.ts | 11 +++++++
 2 files changed, 44 insertions(+)
 create mode 100644 tests/fixtures/errors/opaque-inline-cast.ts

diff --git a/src/semantic/type-assertion-checker.ts b/src/semantic/type-assertion-checker.ts
index 54b0ebc5..832a5a44 100644
--- a/src/semantic/type-assertion-checker.ts
+++ b/src/semantic/type-assertion-checker.ts
@@ -254,6 +254,37 @@ class TypeAssertionChecker {
     }
   }
 
+  private checkOpaqueSource(ta: TypeAssertionNode, fields: InterfaceField[]): void {
+    const inner = ta.expression as { type: string };
+    if (inner.type !== "type_assertion") return;
+    const innerTa = ta.expression as TypeAssertionNode;
+    const src = innerTa.assertedType;
+    if (src !== "unknown" && src !== "any" && src !== "object") return;
+
+    const fieldNames: string[] = [];
+    for (let i = 0; i < fields.length; i++) {
+      fieldNames.push(this.stripOpt((fields[i] as InterfaceField).name));
+    }
+
+    const output = formatCompileError(
+      this.sourceCode,
+      "inline type assertion 'as { " +
+        fieldNames.join("; ") +
+        " }' on opaque source (via 'as " +
+        src +
+        "') produces wrong GEP indices at runtime",
+      ta.loc,
+      "use 'as NamedInterface' instead of inline '{ ... }' when casting from '" + src + "'",
+      [
+        "inline assertion field positions become GEP indices in native code",
+        "opaque sources have no source interface for the prefix checker to verify against",
+        "declare a named interface with the correct field layout and cast to that",
+      ],
+    );
+    process.stderr.write(output);
+    process.exit(1);
+  }
+
   private validateInlineAssertion(ta: TypeAssertionNode): void {
     const assertedType = ta.assertedType;
     if (!assertedType.startsWith("{")) return;
@@ -261,6 +292,8 @@ class TypeAssertionChecker {
     const parsedFields = this.parseInlineFields(assertedType);
     if (parsedFields.length < 2) return;
 
+    this.checkOpaqueSource(ta, parsedFields);
+
     const assertedNames: string[] = [];
     for (let i = 0; i < parsedFields.length; i++) {
       const pf = parsedFields[i] as InterfaceField;
diff --git a/tests/fixtures/errors/opaque-inline-cast.ts b/tests/fixtures/errors/opaque-inline-cast.ts
new file mode 100644
index 00000000..f52ea405
--- /dev/null
+++ b/tests/fixtures/errors/opaque-inline-cast.ts
@@ -0,0 +1,11 @@
+// @test-compile-error: inline type assertion
+interface Node {
+  type: string;
+  value: number;
+  name: string;
+}
+function process(x: Node): number {
+  const y = x as unknown as { type: string; value: number };
+  return y.value;
+}
+console.log(process({ type: "a", value: 42, name: "test" }));

From 43f9cd754d8956618da6b9d442a0374c8458e567 Mon Sep 17 00:00:00 2001
From: cs01 <cs01@users.noreply.github.com>
Date: Sun, 26 Apr 2026 12:09:09 -0700
Subject: [PATCH 2/2] retrigger ci