[conformance] Allow bidi inference of list literals after specialization inference (#2300)

dcreager · web-flow · commit f9664d894c8c · 2026-06-08T12:10:34.000-07:00
diff --git a/conformance/results/mypy/constructors_callable.toml b/conformance/results/mypy/constructors_callable.toml
@@ -43,7 +43,9 @@ constructors_callable.py:145: error: Expression is of type "Class6Any", not "Any
 constructors_callable.py:145: error: Too few arguments  [call-arg]
 constructors_callable.py:164: note: Revealed type is "Overload(def (x: int) -> constructors_callable.Class7[int], def (x: str) -> constructors_callable.Class7[str])"
 constructors_callable.py:184: note: Revealed type is "def [T] (x: list[T], y: list[T]) -> constructors_callable.Class8[T]"
-constructors_callable.py:186: error: Cannot infer function type argument  [misc]
-constructors_callable.py:195: note: Revealed type is "def [T] (x: list[T], y: list[T]) -> constructors_callable.Class9"
-constructors_callable.py:197: error: Cannot infer function type argument  [misc]
+constructors_callable.py:185: error: Argument 2 has incompatible type "str"; expected "list[str]"  [arg-type]
+constructors_callable.py:187: error: Cannot infer function type argument  [misc]
+constructors_callable.py:196: note: Revealed type is "def [T] (x: list[T], y: list[T]) -> constructors_callable.Class9"
+constructors_callable.py:197: error: Argument 2 has incompatible type "str"; expected "list[str]"  [arg-type]
+constructors_callable.py:199: error: Cannot infer function type argument  [misc]
 """
diff --git a/conformance/results/mypy/generics_basic.toml b/conformance/results/mypy/generics_basic.toml
@@ -16,6 +16,13 @@ generics_basic.py:208: error: Dynamic metaclass not supported for "GenericMetaIn
 generics_basic.py:208: error: Type variable "generics_basic.T" is unbound  [valid-type]
 generics_basic.py:208: note: (Hint: Use "Generic[T]" or "Protocol[T]" base class to bind "T" inside a class)
 generics_basic.py:208: note: (Hint: Use "T" in function signature to bind "T" inside a function)
+generics_basic.py:223: error: Argument 2 to "takes_two_lists" has incompatible type "str"; expected "list[int]"  [arg-type]
+generics_basic.py:225: error: Cannot infer value of type parameter "T" of "takes_two_lists"  [misc]
+generics_basic.py:232: error: Cannot infer value of type parameter "T" of "takes_two_lists"  [misc]
+generics_basic.py:240: error: Argument 2 to "takes_two_int_lists" has incompatible type "str"; expected "list[int]"  [arg-type]
+generics_basic.py:241: error: Cannot infer value of type parameter "T_int" of "takes_two_int_lists"  [misc]
+generics_basic.py:244: error: Cannot infer value of type parameter "T_int" of "takes_two_int_lists"  [misc]
+generics_basic.py:251: error: Cannot infer value of type parameter "T_int" of "takes_two_int_lists"  [misc]
 """
 conformance_automated = "Pass"
 errors_diff = """
diff --git a/conformance/results/pycroscope/constructors_callable.toml b/conformance/results/pycroscope/constructors_callable.toml
@@ -21,7 +21,9 @@ output = """
 ./constructors_callable.py:146:0: Takes 0 positional arguments but 1 were given [incompatible_call]
 ./constructors_callable.py:164:4: Revealed type is '(x: ~_Ctor_Class7_T) -> ./constructors_callable.py.Class7[~_Ctor_Class7_T]' [reveal_type]
 ./constructors_callable.py:184:12: Revealed type is '(x: list[~T@./constructors_callable.py.Class8], y: list[~T@./constructors_callable.py.Class8]) -> ./constructors_callable.py.Class8[~T@./constructors_callable.py.Class8]' [reveal_type]
-./constructors_callable.py:186:0: Cannot resolve type variables [incompatible_call]
-./constructors_callable.py:195:12: Revealed type is '(x: list[~T@./constructors_callable.py.Class9.__init__.<locals>.__init__], y: list[~T@./constructors_callable.py.Class9.__init__.<locals>.__init__]) -> ./constructors_callable.py.Class9' [reveal_type]
-./constructors_callable.py:197:0: Cannot resolve type variables [incompatible_call]
+./constructors_callable.py:185:9: Incompatible argument type for y: expected list[~T@./constructors_callable.py.Class8] but got Literal['not a list'] [incompatible_argument]
+./constructors_callable.py:187:0: Cannot resolve type variables [incompatible_call]
+./constructors_callable.py:196:12: Revealed type is '(x: list[~T@./constructors_callable.py.Class9.__init__.<locals>.__init__], y: list[~T@./constructors_callable.py.Class9.__init__.<locals>.__init__]) -> ./constructors_callable.py.Class9' [reveal_type]
+./constructors_callable.py:197:9: Incompatible argument type for y: expected list[~T@./constructors_callable.py.Class9.__init__.<locals>.__init__] but got Literal['not a list'] [incompatible_argument]
+./constructors_callable.py:199:0: Cannot resolve type variables [incompatible_call]
 """
diff --git a/conformance/results/pycroscope/generics_basic.toml b/conformance/results/pycroscope/generics_basic.toml
@@ -15,4 +15,10 @@ output = """
 ./generics_basic.py:171:27: All type parameters for the class must appear within Generic or Protocol [invalid_base]
 ./generics_basic.py:172:27: All type parameters for the class must appear within Generic or Protocol [invalid_base]
 ./generics_basic.py:208:36: Cannot determine metaclass [invalid_metaclass]
+./generics_basic.py:223:21: Incompatible argument type for y: expected list[~T@./generics_basic.py.takes_two_lists.<locals>.takes_two_lists] but got Literal['not a list'] [incompatible_argument]
+./generics_basic.py:225:0: Cannot resolve type variables [incompatible_call]
+./generics_basic.py:232:4: Cannot resolve type variables [incompatible_call]
+./generics_basic.py:240:25: Incompatible argument type for y: expected list[~T_int@./generics_basic.py.takes_two_int_lists.<locals>.takes_two_int_lists] but got Literal['not a list'] [incompatible_argument]
+./generics_basic.py:241:25: Incompatible argument type for y: expected list[~T_int@./generics_basic.py.takes_two_int_lists.<locals>.takes_two_int_lists] but got Literal[['']] [incompatible_argument]
+./generics_basic.py:251:4: Cannot resolve type variables [incompatible_call]
 """
diff --git a/conformance/results/pyrefly/constructors_callable.toml b/conformance/results/pyrefly/constructors_callable.toml
@@ -4,8 +4,7 @@ Converting constructor to callable does not preserve class-scoped type params.
 """
 conformance_automated = "Fail"
 errors_diff = """
-Line 186: Expected 1 errors
-Line 185: Unexpected errors ['assert_type(Class8[Unknown], Class8[str]) failed [assert-type]']
+Line 186: Unexpected errors ['assert_type(Class8[Unknown], Class8[str]) failed [assert-type]']
 """
 output = """
 ERROR constructors_callable.py:38:3-5: Missing argument `x` [missing-argument]
@@ -21,6 +20,8 @@ ERROR constructors_callable.py:82:3-8: Missing argument `x` [missing-argument]
 ERROR constructors_callable.py:82:4-5: Unexpected keyword argument `y` [unexpected-keyword]
 ERROR constructors_callable.py:129:4-5: Expected 0 positional arguments, got 1 [bad-argument-count]
 ERROR constructors_callable.py:146:8-9: Expected 0 positional arguments, got 1 [bad-argument-count]
-ERROR constructors_callable.py:185:12-41: assert_type(Class8[Unknown], Class8[str]) failed [assert-type]
-ERROR constructors_callable.py:197:9-13: Argument `list[str]` is not assignable to parameter `y` with type `list[int]` [bad-argument-type]
+ERROR constructors_callable.py:185:10-22: Argument `Literal['not a list']` is not assignable to parameter `y` with type `list[Unknown]` [bad-argument-type]
+ERROR constructors_callable.py:186:12-41: assert_type(Class8[Unknown], Class8[str]) failed [assert-type]
+ERROR constructors_callable.py:197:10-22: Argument `Literal['not a list']` is not assignable to parameter `y` with type `list[str]` [bad-argument-type]
+ERROR constructors_callable.py:199:9-13: Argument `list[str]` is not assignable to parameter `y` with type `list[int]` [bad-argument-type]
 """
diff --git a/conformance/results/pyrefly/generics_basic.toml b/conformance/results/pyrefly/generics_basic.toml
@@ -15,4 +15,11 @@ ERROR generics_basic.py:163:7-11: Expected a type variable, got `int` [invalid-t
 ERROR generics_basic.py:171:7-11: Class `Bad3` uses type variables not specified in `Generic` or `Protocol` base [invalid-type-var]
 ERROR generics_basic.py:172:7-11: Class `Bad4` uses type variables not specified in `Generic` or `Protocol` base [invalid-type-var]
 ERROR generics_basic.py:208:7-26: Metaclass may not be an unbound generic [invalid-inheritance]
+ERROR generics_basic.py:223:22-34: Argument `Literal['not a list']` is not assignable to parameter `y` with type `list[int]` in function `takes_two_lists` [bad-argument-type]
+ERROR generics_basic.py:225:22-26: Argument `list[str]` is not assignable to parameter `y` with type `list[int]` in function `takes_two_lists` [bad-argument-type]
+ERROR generics_basic.py:232:24-25: Argument `list[str]` is not assignable to parameter `y` with type `list[int]` in function `takes_two_lists` [bad-argument-type]
+ERROR generics_basic.py:240:26-38: Argument `Literal['not a list']` is not assignable to parameter `y` with type `list[int]` in function `takes_two_int_lists` [bad-argument-type]
+ERROR generics_basic.py:241:20-31: `str` is not assignable to upper bound `int` of type variable `T_int` [bad-specialization]
+ERROR generics_basic.py:241:26-30: Argument `list[str]` is not assignable to parameter `y` with type `list[int]` in function `takes_two_int_lists` [bad-argument-type]
+ERROR generics_basic.py:251:28-29: Argument `list[bool]` is not assignable to parameter `y` with type `list[int]` in function `takes_two_int_lists` [bad-argument-type]
 """
diff --git a/conformance/results/pyright/constructors_callable.toml b/conformance/results/pyright/constructors_callable.toml
@@ -1,4 +1,3 @@
-conformant = "Pass"
 conformance_automated = "Pass"
 errors_diff = """
 """
@@ -25,9 +24,13 @@ constructors_callable.py:144:13 - information: Type of "r6_any" is "() -> Any"
 constructors_callable.py:146:8 - error: Expected 0 positional arguments (reportCallIssue)
 constructors_callable.py:164:5 - information: Type of "r7" is "Overload[(x: int) -> Class7[int], (x: str) -> Class7[str]]"
 constructors_callable.py:184:13 - information: Type of "r8" is "(x: list[T@Class8], y: list[T@Class8]) -> Class8[T@Class8]"
-constructors_callable.py:186:10 - error: Argument of type "list[str]" cannot be assigned to parameter "y" of type "list[T@Class8]"
+constructors_callable.py:185:10 - error: Argument of type "Literal['not a list']" cannot be assigned to parameter "y" of type "list[T@Class8]"
+  "Literal['not a list']" is not assignable to "list[str]" (reportArgumentType)
+constructors_callable.py:187:10 - error: Argument of type "list[str]" cannot be assigned to parameter "y" of type "list[T@Class8]"
   "Literal['']" is not assignable to "int" (reportArgumentType)
-constructors_callable.py:195:13 - information: Type of "r9" is "(x: list[T@__init__], y: list[T@__init__]) -> Class9"
-constructors_callable.py:197:10 - error: Argument of type "list[str]" cannot be assigned to parameter "y" of type "list[T@__init__]"
+constructors_callable.py:196:13 - information: Type of "r9" is "(x: list[T@__init__], y: list[T@__init__]) -> Class9"
+constructors_callable.py:197:10 - error: Argument of type "Literal['not a list']" cannot be assigned to parameter "y" of type "list[T@__init__]"
+  "Literal['not a list']" is not assignable to "list[str]" (reportArgumentType)
+constructors_callable.py:199:10 - error: Argument of type "list[str]" cannot be assigned to parameter "y" of type "list[T@__init__]"
   "Literal['']" is not assignable to "int" (reportArgumentType)
 """
diff --git a/conformance/results/pyright/generics_basic.toml b/conformance/results/pyright/generics_basic.toml
@@ -20,6 +20,22 @@ generics_basic.py:171:7 - error: Generic[] or Protocol[] must include all type v
 generics_basic.py:172:7 - error: Generic[] or Protocol[] must include all type variables
   Missing type variables: "T_co" (reportGeneralTypeIssues)
 generics_basic.py:208:37 - error: Metaclass cannot be generic (reportGeneralTypeIssues)
+generics_basic.py:223:22 - error: Argument of type "Literal['not a list']" cannot be assigned to parameter "y" of type "list[T@takes_two_lists]" in function "takes_two_lists"
+  "Literal['not a list']" is not assignable to "list[int]" (reportArgumentType)
+generics_basic.py:225:23 - error: Argument of type "list[str]" cannot be assigned to parameter "y" of type "list[T@takes_two_lists]" in function "takes_two_lists"
+  "Literal['']" is not assignable to "int" (reportArgumentType)
+generics_basic.py:232:24 - error: Argument of type "list[str]" cannot be assigned to parameter "y" of type "list[T@takes_two_lists]" in function "takes_two_lists"
+  "list[str]" is not assignable to "list[int]"
+    Type parameter "_T@list" is invariant, but "str" is not the same as "int"
+    Consider switching from "list" to "Sequence" which is covariant (reportArgumentType)
+generics_basic.py:240:26 - error: Argument of type "Literal['not a list']" cannot be assigned to parameter "y" of type "list[T_int@takes_two_int_lists]" in function "takes_two_int_lists"
+  "Literal['not a list']" is not assignable to "list[int]" (reportArgumentType)
+generics_basic.py:241:27 - error: Argument of type "list[str]" cannot be assigned to parameter "y" of type "list[T_int@takes_two_int_lists]" in function "takes_two_int_lists"
+  "Literal['']" is not assignable to "int" (reportArgumentType)
+generics_basic.py:251:28 - error: Argument of type "list[bool]" cannot be assigned to parameter "y" of type "list[T_int@takes_two_int_lists]" in function "takes_two_int_lists"
+  "list[bool]" is not assignable to "list[int]"
+    Type parameter "_T@list" is invariant, but "bool" is not the same as "int"
+    Consider switching from "list" to "Sequence" which is covariant (reportArgumentType)
 """
 conformance_automated = "Pass"
 errors_diff = """
diff --git a/conformance/results/ty/constructors_callable.toml b/conformance/results/ty/constructors_callable.toml
@@ -42,9 +42,11 @@ constructors_callable.py:164:5: info[revealed-type] Revealed type: `Overload[[T]
 constructors_callable.py:166:1: error[type-assertion-failure] Type `Class7[int] | Class7[str]` does not match asserted type `Class7[int]`
 constructors_callable.py:167:1: error[type-assertion-failure] Type `Class7[int] | Class7[str]` does not match asserted type `Class7[str]`
 constructors_callable.py:184:13: info[revealed-type] Revealed type: `[T](x: list[T], y: list[T]) -> Class8[T]`
-constructors_callable.py:186:4: error[invalid-argument-type] Argument is incorrect: Expected `list[int | str]`, found `list[int]`
-constructors_callable.py:186:9: error[invalid-argument-type] Argument is incorrect: Expected `list[int | str]`, found `list[str]`
-constructors_callable.py:195:13: info[revealed-type] Revealed type: `[T](x: list[T], y: list[T]) -> Class9`
-constructors_callable.py:197:4: error[invalid-argument-type] Argument is incorrect: Expected `list[int | str]`, found `list[int]`
-constructors_callable.py:197:9: error[invalid-argument-type] Argument is incorrect: Expected `list[int | str]`, found `list[str]`
+constructors_callable.py:185:10: error[invalid-argument-type] Argument is incorrect: Expected `list[str]`, found `Literal["not a list"]`
+constructors_callable.py:187:4: error[invalid-argument-type] Argument is incorrect: Expected `list[int | str]`, found `list[int]`
+constructors_callable.py:187:9: error[invalid-argument-type] Argument is incorrect: Expected `list[int | str]`, found `list[str]`
+constructors_callable.py:196:13: info[revealed-type] Revealed type: `[T](x: list[T], y: list[T]) -> Class9`
+constructors_callable.py:197:10: error[invalid-argument-type] Argument is incorrect: Expected `list[str]`, found `Literal["not a list"]`
+constructors_callable.py:199:4: error[invalid-argument-type] Argument is incorrect: Expected `list[int | str]`, found `list[int]`
+constructors_callable.py:199:9: error[invalid-argument-type] Argument is incorrect: Expected `list[int | str]`, found `list[str]`
 """
diff --git a/conformance/results/ty/generics_basic.toml b/conformance/results/ty/generics_basic.toml
@@ -19,4 +19,14 @@ generics_basic.py:163:12: error[invalid-argument-type] `<class 'int'>` is not a
 generics_basic.py:171:1: error[invalid-generic-class] `Generic` base class must include all type variables used in other base classes
 generics_basic.py:172:1: error[invalid-generic-class] `Generic` base class must include all type variables used in other base classes
 generics_basic.py:208:27: error[invalid-metaclass] Generic metaclasses are not supported
+generics_basic.py:223:22: error[invalid-argument-type] Argument to function `takes_two_lists` is incorrect: Expected `list[int]`, found `Literal["not a list"]`
+generics_basic.py:225:17: error[invalid-argument-type] Argument to function `takes_two_lists` is incorrect: Expected `list[int | str]`, found `list[int]`
+generics_basic.py:225:22: error[invalid-argument-type] Argument to function `takes_two_lists` is incorrect: Expected `list[int | str]`, found `list[str]`
+generics_basic.py:232:21: error[invalid-argument-type] Argument to function `takes_two_lists` is incorrect: Expected `list[int | str]`, found `list[int]`
+generics_basic.py:232:24: error[invalid-argument-type] Argument to function `takes_two_lists` is incorrect: Expected `list[int | str]`, found `list[str]`
+generics_basic.py:240:26: error[invalid-argument-type] Argument to function `takes_two_int_lists` is incorrect: Expected `list[int]`, found `Literal["not a list"]`
+generics_basic.py:241:26: error[invalid-argument-type] Argument to function `takes_two_int_lists` is incorrect: Argument type `str` does not satisfy upper bound `int` of type variable `T_int`
+generics_basic.py:241:26: error[invalid-argument-type] Argument to function `takes_two_int_lists` is incorrect: Expected `list[int]`, found `list[str]`
+generics_basic.py:244:26: error[invalid-argument-type] Argument to function `takes_two_int_lists` is incorrect: Expected `list[int]`, found `list[bool]`
+generics_basic.py:251:28: error[invalid-argument-type] Argument to function `takes_two_int_lists` is incorrect: Expected `list[int]`, found `list[bool]`
 """
diff --git a/conformance/results/zuban/constructors_callable.toml b/conformance/results/zuban/constructors_callable.toml
@@ -21,7 +21,9 @@ constructors_callable.py:144: note: Revealed type is "def () -> Any"
 constructors_callable.py:146: error: Too many arguments  [call-arg]
 constructors_callable.py:164: note: Revealed type is "Overload(def (x: builtins.int) -> tests.constructors_callable.Class7[builtins.int], def (x: builtins.str) -> tests.constructors_callable.Class7[builtins.str])"
 constructors_callable.py:184: note: Revealed type is "def [T] (x: builtins.list[T], y: builtins.list[T]) -> tests.constructors_callable.Class8[T]"
-constructors_callable.py:186: error: List item 0 has incompatible type "str"; expected "int"  [list-item]
-constructors_callable.py:195: note: Revealed type is "def [T] (x: builtins.list[T], y: builtins.list[T]) -> tests.constructors_callable.Class9"
-constructors_callable.py:197: error: List item 0 has incompatible type "str"; expected "int"  [list-item]
+constructors_callable.py:185: error: Argument 2 has incompatible type "str"; expected "list[str]"  [arg-type]
+constructors_callable.py:187: error: List item 0 has incompatible type "str"; expected "int"  [list-item]
+constructors_callable.py:196: note: Revealed type is "def [T] (x: builtins.list[T], y: builtins.list[T]) -> tests.constructors_callable.Class9"
+constructors_callable.py:197: error: Argument 2 has incompatible type "str"; expected "list[str]"  [arg-type]
+constructors_callable.py:199: error: List item 0 has incompatible type "str"; expected "int"  [list-item]
 """
diff --git a/conformance/results/zuban/generics_basic.toml b/conformance/results/zuban/generics_basic.toml
@@ -15,4 +15,12 @@ generics_basic.py:163: error: Free type variable expected in Protocol[...]  [mis
 generics_basic.py:171: error: If Generic[...] or Protocol[...] is present it should list all type variables  [misc]
 generics_basic.py:172: error: If Generic[...] or Protocol[...] is present it should list all type variables  [misc]
 generics_basic.py:208: error: Invalid metaclass "GenericMeta[T]"  [metaclass]
+generics_basic.py:223: error: Argument 2 to "takes_two_lists" has incompatible type "str"; expected "list[int]"  [arg-type]
+generics_basic.py:225: error: List item 0 has incompatible type "str"; expected "int"  [list-item]
+generics_basic.py:232: error: Argument 2 to "takes_two_lists" has incompatible type "list[str]"; expected "list[int]"  [arg-type]
+generics_basic.py:240: error: Argument 2 to "takes_two_int_lists" has incompatible type "str"; expected "list[int]"  [arg-type]
+generics_basic.py:241: error: List item 0 has incompatible type "str"; expected "int"  [list-item]
+generics_basic.py:251: error: Argument 2 to "takes_two_int_lists" has incompatible type "list[bool]"; expected "list[int]"  [arg-type]
+generics_basic.py:251: note: "List" is invariant -- see https://mypy.readthedocs.io/en/stable/common_issues.html#variance
+generics_basic.py:251: note: Consider using "Sequence" instead, which is covariant
 """
diff --git a/conformance/tests/constructors_callable.py b/conformance/tests/constructors_callable.py
@@ -182,8 +182,9 @@ def __new__(cls, x: list[T], y: list[T]) -> Self:
 
 r8 = accepts_callable(Class8)
 reveal_type(r8)  # `def [T] (x: list[T], y: list[T]) -> Class8[T]`
+r8([""], "not a list")  # E: no assignment of T makes the second argument valid
 assert_type(r8([""], [""]), Class8[str])
-r8([1], [""])  # E
+r8([1], [""])  # E?: T = int | str is a potential solution
 
 
 class Class9:
@@ -193,5 +194,6 @@ def __init__(self, x: list[T], y: list[T]) -> None:
 
 r9 = accepts_callable(Class9)
 reveal_type(r9)  # `def [T] (x: list[T], y: list[T]) -> Class9`
+r9([""], "not a list")  # E: no assignment of T makes the second argument valid
 assert_type(r9([""], [""]), Class9)
-r9([1], [""])  # E
+r9([1], [""])  # E?: T = int | str is a potential solution
diff --git a/conformance/tests/generics_basic.py b/conformance/tests/generics_basic.py
