Clarification: unpacked arguments

python · rchen152 · Apr 8, 2026 · Apr 8, 2026 · Apr 8, 2026 · Apr 8, 2026
commit 891f7ae7f39c13698f96dfcd994076adf3a7dcb3
diff --git a/conformance/results/mypy/overloads_evaluation.toml b/conformance/results/mypy/overloads_evaluation.toml
@@ -3,6 +3,7 @@ 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.
+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.
 """
@@ -19,6 +20,7 @@ Line 284: Unexpected errors ['overloads_evaluation.py:284: error: Expression is
 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 395: Unexpected errors ['overloads_evaluation.py:395: error: Expression is of type "Any", not "int"  [assert-type]']
+Line 437: Unexpected errors ['overloads_evaluation.py:437: 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]
@@ -52,4 +54,5 @@ overloads_evaluation.py:284: error: Expression is of type "list[Any]", not "Any"
 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:395: error: Expression is of type "Any", not "int"  [assert-type]
+overloads_evaluation.py:437: error: Expression is of type "Any", not "bool"  [assert-type]
 """
diff --git a/conformance/results/results.html b/conformance/results/results.html
@@ -794,9 +794,9 @@ <h3>Python Type System Conformance Test Results</h3>
 <th class="column col2 conformant">Pass</th>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;overloads_evaluation</th>
-<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not expand boolean arguments to Literal[True] and Literal[False].</p><p>Does not expand enum arguments to literal variants.</p><p>Does not expand tuple arguments to possible combinations.</p><p>Does not evaluate Any in some cases where overload is ambiguous.</p><p>Evaluates Any in some cases where overload is not ambiguous.</p></span></div></th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not expand boolean arguments to Literal[True] and Literal[False].</p><p>Does not expand enum arguments to literal variants.</p><p>Does not expand tuple arguments to possible combinations.</p><p>Does not handle unpacked arguments when checking for parameter type equivalence.</p><p>Does not evaluate Any in some cases where overload is ambiguous.</p><p>Evaluates Any in some cases where overload is not ambiguous.</p></span></div></th>
 <th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not evaluate Any in some cases where overload is ambiguous.</p><p>Picks first overload instead of most general return type in some cases where overload is ambiguous.</p></span></div></th>
-<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Returns Any instead of most general return type for ambiguous calls.</p></span></div></th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not handle unpacked arguments when checking for parameter type equivalence.</p><p>Returns Any instead of most general return type for ambiguous calls.</p></span></div></th>
 <th class="column col2 conformant">Pass</th>
 <th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Returns Any instead of most general return type for ambiguous calls.</p></span></div></th>
 </tr>

diff --git a/conformance/results/zuban/overloads_evaluation.toml b/conformance/results/zuban/overloads_evaluation.toml
@@ -1,10 +1,12 @@
 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 395: Unexpected errors ['overloads_evaluation.py:395: error: Expression is of type "Any", not "int"  [misc]']
+Line 437: Unexpected errors ['overloads_evaluation.py:437: error: Expression is of type "Any", not "bool"  [misc]']
 Line 464: Unexpected errors ['overloads_evaluation.py:464: error: Expression is of type "Any", not "A[Any]"  [misc]']
 """
 output = """
@@ -23,5 +25,6 @@ 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:395: error: Expression is of type "Any", not "int"  [misc]
+overloads_evaluation.py:437: error: Expression is of type "Any", not "bool"  [misc]
 overloads_evaluation.py:464: error: Expression is of type "Any", not "A[Any]"  [misc]
 """
diff --git a/conformance/tests/overloads_evaluation.py b/conformance/tests/overloads_evaluation.py
@@ -420,21 +420,21 @@ def check_example10(x: Any):
 
 
 @overload
-def example11(x: int) -> bool: ...
+def example11(x: Literal['o1'], y: int, z: str) -> bool: ...
 
 
 @overload
-def example11(**kwargs: int) -> int: ...
+def example11(x: str, y: int, z: str) -> int: ...
 
 
-def example11(*args: int, **kwargs: int) -> int:
-    return 0
+def example11(x: str, y: int, z: str) -> bool | int:
+    return True
+
 
 def check_example11(x: Any):
-    # The parameters corresponding to argument `x` (`x` in the first overload
-    # and `**kwargs` in the second) both have type `int`, so the second
-    # overload can be eliminated.
-    assert_type(example11(x=x), bool)
+    # `*x` maps to `(y: int, z: str)` in both overloads, so the second overload
+    # can be eliminated.
+    assert_type(example11('o1', *x), bool)
 
 
 class A[T]:

diff --git a/docs/spec/overload.rst b/docs/spec/overload.rst
@@ -271,10 +271,13 @@ Step 5
 For each of the candidate 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 candidate overloads
-  are :term:`equivalent`.
+- 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 candidate
+  overloads are :term:`equivalent`. For an unpacked argument, this condition is
+  satisfied if the argument maps to the same number of parameters in all
+  candidate overloads, and for each parameter, the types in all candidate
+  overloads are equivalent.
 
 If so, eliminate all of the subsequent candidate overloads.