add test for step 4 in overload matching

Author: carljm

conformance/results/mypy/version.toml

@@ -1,2 +1,2 @@
 version = "mypy 1.14.1"
-test_duration = 1.7
+test_duration = 1.8

conformance/results/pyre/overloads_evaluation.toml

@@ -4,6 +4,7 @@ Does not expand boolean arguments to Literal[True] and Literal[False].
 Does not expand enum arguments to literal variants.
 Does not expand type[A | B] to type[A] and type[B].
 Does not expand tuple arguments to possible combinations.
+Does not prefer variadic match to indeterminate-length unpacked argument.
 """
 conformance_automated = "Fail"
 errors_diff = """
@@ -17,6 +18,7 @@ Line 144: Unexpected errors ['overloads_evaluation.py:144:29 Incompatible parame
 Line 145: Unexpected errors ['overloads_evaluation.py:145:4 Assert type [70]: Expected `Union[int, str]` but got `int`.']
 Line 166: Unexpected errors ['overloads_evaluation.py:166:24 Incompatible parameter type [6]: In call `expand_tuple`, for 1st positional argument, expected `Tuple[int, int]` but got `Tuple[int, Union[int, str]]`.']
 Line 167: Unexpected errors ['overloads_evaluation.py:167:4 Assert type [70]: Expected `Union[int, str]` but got `int`.']
+Line 193: Unexpected errors ['overloads_evaluation.py:193:4 Assert type [70]: Expected `int` but got `typing_extensions.Literal[0]`.']
 """
 output = """
 overloads_evaluation.py:27:0 Missing argument [20]: Call `example1` expects argument `x`.
@@ -34,4 +36,5 @@ overloads_evaluation.py:144:29 Incompatible parameter type [6]: In call `expand_
 overloads_evaluation.py:145:4 Assert type [70]: Expected `Union[int, str]` but got `int`.
 overloads_evaluation.py:166:24 Incompatible parameter type [6]: In call `expand_tuple`, for 1st positional argument, expected `Tuple[int, int]` but got `Tuple[int, Union[int, str]]`.
 overloads_evaluation.py:167:4 Assert type [70]: Expected `Union[int, str]` but got `int`.
+overloads_evaluation.py:193:4 Assert type [70]: Expected `int` but got `typing_extensions.Literal[0]`.
 """

conformance/results/pyre/version.toml

@@ -1,2 +1,2 @@
 version = "pyre 0.9.23"
-test_duration = 5.9
+test_duration = 6.0

conformance/results/pyright/version.toml

@@ -1,2 +1,2 @@
 version = "pyright 1.1.391"
-test_duration = 1.5
+test_duration = 1.6

conformance/results/pytype/overloads_evaluation.toml

@@ -21,6 +21,7 @@ Line 141: Unexpected errors ['overloads_evaluation.py:141:12: \\x1b[1m\\x1b[31me
 Line 145: Unexpected errors ['overloads_evaluation.py:145:5: \\x1b[1m\\x1b[31merror\\x1b[39m\\x1b[0m: in check_expand_type_union: int [assert-type]']
 Line 163: Unexpected errors ['overloads_evaluation.py:163:12: \\x1b[1m\\x1b[31merror\\x1b[39m\\x1b[0m: in expand_tuple: bad return type [bad-return-type]']
 Line 167: Unexpected errors ['overloads_evaluation.py:167:5: \\x1b[1m\\x1b[31merror\\x1b[39m\\x1b[0m: in check_expand_tuple: int [assert-type]']
+Line 185: Unexpected errors ['overloads_evaluation.py:185:12: \\x1b[1m\\x1b[31merror\\x1b[39m\\x1b[0m: in variadic: bad return type [bad-return-type]']
 """
 output = """
 overloads_evaluation.py:23:12: \u001b[1m\u001b[31merror\u001b[39m\u001b[0m: in example1: bad return type [bad-return-type]
@@ -120,4 +121,9 @@ overloads_evaluation.py:167:5: \u001b[1m\u001b[31merror\u001b[39m\u001b[0m: in c
     assert_type(ret1, int | str)
     \u001b[1m\u001b[31m~~~~~~~~~~~~~~~~~~~~~~~~~~~~\u001b[39m\u001b[0m
 
+overloads_evaluation.py:185:12: \u001b[1m\u001b[31merror\u001b[39m\u001b[0m: in variadic: bad return type [bad-return-type]
+
+    return 1
+           \u001b[1m\u001b[31m~\u001b[39m\u001b[0m
+
 """

conformance/results/pytype/version.toml

@@ -1,2 +1,2 @@
 version = "pytype 2024.10.11"
-test_duration = 31.0
+test_duration = 31.2

conformance/results/results.html

@@ -159,16 +159,16 @@ <h3>Python Type System Conformance Test Results</h3>
         <div class="table_container"><table><tbody>
 <tr><th class="col1">&nbsp;</th>
 <th class='tc-header'><div class='tc-name'>mypy 1.14.1</div>
-<div class='tc-time'>1.7sec</div>
+<div class='tc-time'>1.8sec</div>
 </th>
 <th class='tc-header'><div class='tc-name'>pyright 1.1.391</div>
-<div class='tc-time'>1.5sec</div>
+<div class='tc-time'>1.6sec</div>
 </th>
 <th class='tc-header'><div class='tc-name'>pyre 0.9.23</div>
-<div class='tc-time'>5.9sec</div>
+<div class='tc-time'>6.0sec</div>
 </th>
 <th class='tc-header'><div class='tc-name'>pytype 2024.10.11</div>
-<div class='tc-time'>31.0sec</div>
+<div class='tc-time'>31.2sec</div>
 </th>
 </tr>
 <tr><th class="column" colspan="5">
@@ -693,7 +693,7 @@ <h3>Python Type System Conformance Test Results</h3>
 <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 pick a winning overload based on arity, prior to considering argument types.</p><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></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></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 type[A | B] to type[A] and type[B].</p><p>Does not expand tuple arguments to possible combinations.</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 type[A | B] to type[A] and type[B].</p><p>Does not expand tuple arguments to possible combinations.</p><p>Does not prefer variadic match to indeterminate-length unpacked argument.</p></span></div></th>
 <th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not pick a winning overload based on arity, prior to considering argument types.</p><p>Does not perform argument expansion (on any types) when matching overloads.</p></span></div></th>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;overloads_overlap</th>

conformance/tests/overloads_evaluation.py

@@ -166,3 +166,28 @@ def check_expand_tuple(v: int | str) -> None:
     ret1 = expand_tuple((1, v))
     assert_type(ret1, int | str)
 
+
+# > Step 4: If the argument list is compatible with two or more overloads,
+# > determine whether one or more of the overloads has a variadic parameter
+# > (either ``*args`` or ``**kwargs``) that maps to a corresponding argument
+# > that supplies an indeterminate number of positional or keyword arguments.
+# > If so, eliminate overloads that do not have a variadic parameter.
+
+@overload
+def variadic(x: int, /) -> Literal[0]:
+    ...
+
+@overload
+def variadic(*args: int) -> int:
+    ...
+
+def variadic(*args: int) -> int | str:
+    return 1
+
+# > - If this results in only one remaining candidate overload, it is
+# >   the winning match. Evaluate it as if it were a non-overloaded function
+# >   call and stop.
+
+def check_variadic(v: list[int]) -> None:
+    ret1 = variadic(*v)
+    assert_type(ret1, int)