python · rchen152 · Apr 8, 2026 · Apr 8, 2026 · Apr 8, 2026 · Apr 8, 2026
diff --git a/conformance/results/mypy/overloads_evaluation.toml b/conformance/results/mypy/overloads_evaluation.toml
@@ -3,8 +3,14 @@ notes = """
 Does not expand boolean arguments to `Literal[True]` and `Literal[False]`.
 Does not expand enum arguments to literal variants.
 Does not expand tuple arguments to possible combinations.
+<<<<<<< HEAD
+Does not handle unpacked arguments when checking for parameter type equivalence.
+Does not evaluate Any in some cases where overload is ambiguous.
+Evaluates Any in some cases where overload is not ambiguous.
+=======
 Does not evaluate `Any` in some cases where overload is ambiguous.
 Evaluates `Any` in some cases where overload is not ambiguous.
+>>>>>>> main
 """
 conformance_automated = "Fail"
 errors_diff = """
@@ -14,10 +20,11 @@ Line 161: Unexpected errors ['overloads_evaluation.py:161: error: No overload va
 Line 162: Unexpected errors ['overloads_evaluation.py:162: error: Expression is of type "Any", not "Literal[0, 1]"  [assert-type]']
 Line 205: Unexpected errors ['overloads_evaluation.py:205: error: Argument 1 to "expand_tuple" has incompatible type "tuple[int, int | str]"; expected "tuple[int, int]"  [arg-type]']
 Line 206: Unexpected errors ['overloads_evaluation.py:206: error: Expression is of type "int", not "int | str"  [assert-type]']
-Line 265: Unexpected errors ['overloads_evaluation.py:265: error: Expression is of type "list[Any]", not "Any"  [assert-type]']
-Line 281: Unexpected errors ['overloads_evaluation.py:281: error: Expression is of type "list[Any]", not "Any"  [assert-type]']
-Line 303: Unexpected errors ['overloads_evaluation.py:303: error: Expression is of type "Any", not "float"  [assert-type]']
-Line 347: Unexpected errors ['overloads_evaluation.py:347: error: Expression is of type "list[Any]", not "Any"  [assert-type]']
+Line 268: Unexpected errors ['overloads_evaluation.py:268: error: Expression is of type "list[Any]", not "Any"  [assert-type]']
+Line 284: Unexpected errors ['overloads_evaluation.py:284: error: Expression is of type "list[Any]", not "Any"  [assert-type]']
+Line 306: Unexpected errors ['overloads_evaluation.py:306: error: Expression is of type "Any", not "float"  [assert-type]']
+Line 350: Unexpected errors ['overloads_evaluation.py:350: error: Expression is of type "list[Any]", not "Any"  [assert-type]']
+Line 439: Unexpected errors ['overloads_evaluation.py:439: error: Expression is of type "Any", not "bool"  [assert-type]']
 """
 output = """
 overloads_evaluation.py:38: error: All overload variants of "example1_1" require at least one argument  [call-overload]
@@ -46,8 +53,9 @@ overloads_evaluation.py:161: note:     def expand_enum(x: Literal[Color.BLUE]) -
 overloads_evaluation.py:162: error: Expression is of type "Any", not "Literal[0, 1]"  [assert-type]
 overloads_evaluation.py:205: error: Argument 1 to "expand_tuple" has incompatible type "tuple[int, int | str]"; expected "tuple[int, int]"  [arg-type]
 overloads_evaluation.py:206: error: Expression is of type "int", not "int | str"  [assert-type]
-overloads_evaluation.py:265: error: Expression is of type "list[Any]", not "Any"  [assert-type]
-overloads_evaluation.py:281: error: Expression is of type "list[Any]", not "Any"  [assert-type]
-overloads_evaluation.py:303: error: Expression is of type "Any", not "float"  [assert-type]
-overloads_evaluation.py:347: error: Expression is of type "list[Any]", not "Any"  [assert-type]
+overloads_evaluation.py:268: error: Expression is of type "list[Any]", not "Any"  [assert-type]
+overloads_evaluation.py:284: error: Expression is of type "list[Any]", not "Any"  [assert-type]
+overloads_evaluation.py:306: error: Expression is of type "Any", not "float"  [assert-type]
+overloads_evaluation.py:350: error: Expression is of type "list[Any]", not "Any"  [assert-type]
+overloads_evaluation.py:439: error: Expression is of type "Any", not "bool"  [assert-type]
 """
diff --git a/conformance/results/pycroscope/overloads_evaluation.toml b/conformance/results/pycroscope/overloads_evaluation.toml
@@ -1,9 +1,21 @@
-conformance_automated = "Pass"
+conformance_automated = "Fail"
 errors_diff = """
+Line 371: Unexpected errors ['./overloads_evaluation.py:371:16:   Any[multiple_overload_matches] is not equivalent to bool']
+Line 400: Unexpected errors ['./overloads_evaluation.py:400:16:   Any[multiple_overload_matches] is not equivalent to bool']
+Line 420: Unexpected errors ['./overloads_evaluation.py:420:16:   Any[multiple_overload_matches] is not equivalent to bool']
+Line 439: Unexpected errors ['./overloads_evaluation.py:439:16:   Any[multiple_overload_matches] is not equivalent to bool']
+Line 441: Unexpected errors ['./overloads_evaluation.py:441:16:   Any[multiple_overload_matches] is not equivalent to bool']
+Line 468: Unexpected errors ['./overloads_evaluation.py:468:16:   Any[multiple_overload_matches] is not equivalent to ./overloads_evaluation.py.A[Any[explicit]]']
 """
 output = """
 ./overloads_evaluation.py:38:0: Cannot call overloaded function [incompatible_call]
 ./overloads_evaluation.py:46:0: Cannot call overloaded function [incompatible_argument]
 ./overloads_evaluation.py:51:0: Cannot call overloaded function [incompatible_argument]
 ./overloads_evaluation.py:116:4: Cannot call overloaded function [incompatible_argument]
+./overloads_evaluation.py:371:16:   Any[multiple_overload_matches] is not equivalent to bool
+./overloads_evaluation.py:400:16:   Any[multiple_overload_matches] is not equivalent to bool
+./overloads_evaluation.py:420:16:   Any[multiple_overload_matches] is not equivalent to bool
+./overloads_evaluation.py:439:16:   Any[multiple_overload_matches] is not equivalent to bool
+./overloads_evaluation.py:441:16:   Any[multiple_overload_matches] is not equivalent to bool
+./overloads_evaluation.py:468:16:   Any[multiple_overload_matches] is not equivalent to ./overloads_evaluation.py.A[Any[explicit]]
 """
diff --git a/conformance/results/pyrefly/overloads_evaluation.toml b/conformance/results/pyrefly/overloads_evaluation.toml
@@ -1,10 +1,12 @@
 conformant = "Pass"
-conformance_automated = "Pass"
+conformance_automated = "Fail"
 errors_diff = """
+Line 395: Unexpected errors ['assert_type(int, Any) failed [assert-type]']
 """
 output = """
 ERROR overloads_evaluation.py:38:11-13: No matching overload found for function `example1_1` called with arguments: () [no-matching-overload]
 ERROR overloads_evaluation.py:46:15-16: Argument `Literal[1]` is not assignable to parameter `y` with type `str` in function `example1_1` [bad-argument-type]
 ERROR overloads_evaluation.py:51:12-13: Argument `Literal[1]` is not assignable to parameter `x` with type `str` in function `example1_1` [bad-argument-type]
 ERROR overloads_evaluation.py:116:13-22: No matching overload found for function `example2` called with arguments: (int | str, int | str, Literal[1]) [no-matching-overload]
+ERROR overloads_evaluation.py:395:16-27: assert_type(int, Any) failed [assert-type]
 """
diff --git a/conformance/results/pyright/overloads_evaluation.toml b/conformance/results/pyright/overloads_evaluation.toml
@@ -1,10 +1,17 @@
 conformant = "Partial"
 notes = """
+<<<<<<< HEAD
+Does not evaluate Any in some cases where overload is ambiguous.
+Picks first overload instead of most general return type in some cases where overload is ambiguous.
+=======
 Does not evaluate `Any` in some cases where overload is ambiguous.
+>>>>>>> main
 """
 conformance_automated = "Fail"
 errors_diff = """
-Line 281: Unexpected errors ['overloads_evaluation.py:281:17 - error: "assert_type" mismatch: expected "Any" but received "list[int]" (reportAssertTypeFailure)']
+Line 284: Unexpected errors ['overloads_evaluation.py:284:17 - error: "assert_type" mismatch: expected "Any" but received "list[int]" (reportAssertTypeFailure)']
+Line 395: Unexpected errors ['overloads_evaluation.py:395:17 - error: "assert_type" mismatch: expected "Any" but received "int" (reportAssertTypeFailure)']
+Line 468: Unexpected errors ['overloads_evaluation.py:468:17 - error: "assert_type" mismatch: expected "A[Any]" but received "A[None]" (reportAssertTypeFailure)']
 """
 output = """
 overloads_evaluation.py:38:1 - error: No overloads for "example1_1" match the provided arguments
@@ -20,5 +27,7 @@ overloads_evaluation.py:116:14 - error: Argument of type "int | str" cannot be a
 overloads_evaluation.py:116:17 - error: Argument of type "int | str" cannot be assigned to parameter "y" of type "int" in function "example2"
   Type "int | str" is not assignable to type "int"
     "str" is not assignable to "int" (reportArgumentType)
-overloads_evaluation.py:281:17 - error: "assert_type" mismatch: expected "Any" but received "list[int]" (reportAssertTypeFailure)
+overloads_evaluation.py:284:17 - error: "assert_type" mismatch: expected "Any" but received "list[int]" (reportAssertTypeFailure)
+overloads_evaluation.py:395:17 - error: "assert_type" mismatch: expected "Any" but received "int" (reportAssertTypeFailure)
+overloads_evaluation.py:468:17 - error: "assert_type" mismatch: expected "A[Any]" but received "A[None]" (reportAssertTypeFailure)
 """
diff --git a/conformance/results/results.html b/conformance/results/results.html
diff --git a/conformance/results/ty/overloads_evaluation.toml b/conformance/results/ty/overloads_evaluation.toml
@@ -1,9 +1,15 @@
-conformance_automated = "Pass"
+conformant = "Partial"
+notes = """
+Returns Any instead of most general return type for ambiguous calls.
+"""
+conformance_automated = "Fail"
 errors_diff = """
+Line 468: Unexpected errors ['overloads_evaluation.py:468:5: error[type-assertion-failure] Type `Unknown` does not match asserted type `A[Any]`']
 """
 output = """
 overloads_evaluation.py:38:1: error[no-matching-overload] No overload of function `example1_1` matches arguments
 overloads_evaluation.py:46:15: error[invalid-argument-type] Argument to function `example1_1` is incorrect: Expected `str`, found `Literal[1]`
 overloads_evaluation.py:51:12: error[invalid-argument-type] Argument to function `example1_1` is incorrect: Expected `str`, found `Literal[1]`
 overloads_evaluation.py:116:5: error[no-matching-overload] No overload of function `example2` matches arguments
+overloads_evaluation.py:468:5: error[type-assertion-failure] Type `Unknown` does not match asserted type `A[Any]`
 """
diff --git a/conformance/results/zuban/overloads_evaluation.toml b/conformance/results/zuban/overloads_evaluation.toml
@@ -1,5 +1,12 @@
-conformance_automated = "Pass"
+conformant = "Partial"
+notes = """
+Does not handle unpacked arguments when checking for parameter type equivalence.
+Returns Any instead of most general return type for ambiguous calls.
+"""
+conformance_automated = "Fail"
 errors_diff = """
+Line 439: Unexpected errors ['overloads_evaluation.py:439: error: Expression is of type "Any", not "bool"  [misc]']
+Line 468: Unexpected errors ['overloads_evaluation.py:468: error: Expression is of type "Any", not "A[Any]"  [misc]']
 """
 output = """
 overloads_evaluation.py:38: error: All overload variants of "example1_1" require at least one argument  [call-overload]
@@ -16,4 +23,6 @@ overloads_evaluation.py:51: note:     def example1_1(x: int, y: str) -> int
 overloads_evaluation.py:51: note:     def example1_1(x: str) -> str
 overloads_evaluation.py:116: error: Argument 1 to "example2" has incompatible type "int | str"; expected "int"  [arg-type]
 overloads_evaluation.py:116: error: Argument 2 to "example2" has incompatible type "int | str"; expected "str"  [arg-type]
+overloads_evaluation.py:439: error: Expression is of type "Any", not "bool"  [misc]
+overloads_evaluation.py:468: error: Expression is of type "Any", not "A[Any]"  [misc]
 """
diff --git a/conformance/tests/overloads_evaluation.py b/conformance/tests/overloads_evaluation.py
@@ -235,10 +235,13 @@ def check_variadic(v: list[int]) -> None:
     assert_type(ret1, int)
 
 
-# > Step 5: For all arguments, determine whether all possible
-# > :term:`materializations <materialize>` of the argument's type are assignable to
-# > the corresponding parameter type for each of the remaining overloads. If so,
-# > eliminate all of the subsequent remaining overloads.
+# > Step 5: For each of the remaining overloads, determine whether all
+# > arguments satisfy at least one of the following conditions:
+# > - All possible :term:`materializations <materialize>` of the argument's type are
+# >   assignable to the corresponding parameter type, or
+# > - The parameter types corresponding to this argument in all of the remaining overloads
+# >   are :term:`equivalent`.
+# > If so, eliminate all of the subsequent remaining overloads.
 
 
 @overload
@@ -345,3 +348,121 @@ def check_example7(v1: list[Any], v2: Any) -> None:
 
     ret3 = example7(v1, v2)
     assert_type(ret3, Any)
+
+
+@overload
+def example8(x: str, y: Literal['o1']) -> bool: ...
+
+
+@overload
+def example8(x: str, y: str) -> int: ...
+
+
+def example8(x: str, y: str) -> bool | int:
+    return True
+
+
+def check_example8(x: Any):
+    # The parameter type corresponding to argument `x` is `str` in both
+    # overloads, and all materializations of argument `y`'s type of
+    # `Literal['o1']` match the first overload, so the second overload can be
+    # eliminated.
+    ret = example8(x, 'o1')
+    assert_type(ret, bool)
+
+
+@overload
+def example9(x: str, y: Literal['o1']) -> bool: ...
+
+
+@overload
+def example9(x: bytes, y: Literal['o1', 'o2']) -> bool: ...
+
+
+@overload
+def example9(x: bytes, y: str) -> int: ...
+
+
+def example9(x: str | bytes, y: str) -> bool | int:
+    return True
+
+
+def check_example9(x: Any):
+    # All three overloads are candidates. The parameter types corresponding to
+    # argument `x` are `str` and `bytes`, which are not equivalent, so none of
+    # the overloads can be eliminated. We fall back to `Any`.
+    ret1 = example9(x, 'o1')
+    assert_type(ret1, Any)
+    # The second and third overload are candidates. The parameter type
+    # corresponding to argument `x` is `bytes` in both candidates, so we can
+    # eliminate the third overload.
+    ret2 = example9(x, 'o2')
+    assert_type(ret2, bool)
+
+
+@overload
+def example10(x: int) -> bool: ...
+
+
+@overload
+def example10(*args: int) -> int: ...
+
+
+def example10(*args: int, **kwargs: int) -> int:
+    return 0
+
+
+def check_example10(x: Any):
+    # The parameters corresponding to argument `x` (`x` in the first overload
+    # and `*args` in the second) both have type `int`, so the second overload
+    # can be eliminated.
+    ret = example10(x)
+    assert_type(ret, bool)
+
+
+@overload
+def example11(x: Literal['o1'], y: int, z: str) -> bool: ...
+
+
+@overload
+def example11(x: str, y: int, z: str) -> int: ...
+
+
+def example11(x: str, y: int, z: str) -> bool | int:
+    return True
+
+
+def check_example11(x: Any):
+    # `*x` maps to `(y: int, z: str)` in both overloads, so the second overload
+    # can be eliminated.
+    ret1 = example11('o1', *x)
+    assert_type(ret1, bool)
+    ret2 = example11('o1', x, x)
+    assert_type(ret2, bool)
+
+
+class A[T]:
+    x: T
+
+    def f(self) -> T:
+        return self.x
+
+
+@overload
+def example12(x: A[None]) -> A[None]: ...
+
+
+@overload
+def example12(x: A[Any]) -> A[Any]: ...
+
+
+def example12(x: A[Any]) -> A[Any]:
+    return x
+
+
+def check_example12(x: Any):
+    # Step 5 eliminates the first overload because there exists a
+    # materialization of `A[Any]` that is not assignable to `A[None]`. Step 6
+    # picks the second overload.
+    ret = example12(x)
+    assert_type(ret, A[Any])