Fix crash on star unpacking to underscore

mypy/checker.py

@@ -192,7 +192,6 @@
     Overloaded,
     PartialType,
     ProperType,
-    StarType,
     TupleType,
     Type,
     TypeAliasType,
@@ -3288,7 +3287,7 @@ def check_assignment_to_multiple_lvalues(
             last_idx: int | None = None
             for idx_rval, rval in enumerate(rvalue.items):
                 if isinstance(rval, StarExpr):
-                    typs = get_proper_type(self.expr_checker.visit_star_expr(rval).type)
+                    typs = get_proper_type(self.expr_checker.accept(rval.expr))
                     if isinstance(typs, TupleType):
                         rvalues.extend([TempNode(typ) for typ in typs.items])
                     elif self.type_is_iterable(typs) and isinstance(typs, Instance):
@@ -3311,7 +3310,7 @@ def check_assignment_to_multiple_lvalues(
             iterable_end: int | None = None
             for i, rval in enumerate(rvalues):
                 if isinstance(rval, StarExpr):
-                    typs = get_proper_type(self.expr_checker.visit_star_expr(rval).type)
+                    typs = get_proper_type(self.expr_checker.accept(rval.expr))
                     if self.type_is_iterable(typs) and isinstance(typs, Instance):
                         if iterable_start is None:
                             iterable_start = i
@@ -3674,8 +3673,7 @@ def check_lvalue(self, lvalue: Lvalue) -> tuple[Type | None, IndexExpr | None, V
             ]
             lvalue_type = TupleType(types, self.named_type("builtins.tuple"))
         elif isinstance(lvalue, StarExpr):
-            typ, _, _ = self.check_lvalue(lvalue.expr)
-            lvalue_type = StarType(typ) if typ else None
+            lvalue_type, _, _ = self.check_lvalue(lvalue.expr)
         else:
             lvalue_type = self.expr_checker.accept(lvalue)
 

mypy/checkexpr.py

@@ -140,7 +140,6 @@
     ParamSpecType,
     PartialType,
     ProperType,
-    StarType,
     TupleType,
     Type,
     TypeAliasType,
@@ -5156,8 +5155,9 @@ def visit_typeddict_expr(self, e: TypedDictExpr) -> Type:
     def visit__promote_expr(self, e: PromoteExpr) -> Type:
         return e.type
 
-    def visit_star_expr(self, e: StarExpr) -> StarType:
-        return StarType(self.accept(e.expr))
+    def visit_star_expr(self, e: StarExpr) -> Type:
+        # TODO: should this ever be called (see e.g. mypyc visitor)?
+        return self.accept(e.expr)
 
     def object_type(self) -> Instance:
         """Return instance type 'object'."""

mypy/test/testpythoneval.py

@@ -81,6 +81,10 @@ def test_python_evaluation(testcase: DataDrivenTestCase, cache_dir: str) -> None
             # Normalize paths so that the output is the same on Windows and Linux/macOS.
             line = line.replace(test_temp_dir + os.sep, test_temp_dir + "/")
             output.append(line.rstrip("\r\n"))
+    if returncode > 1 and not testcase.output:
+        # Either api.run() doesn't work well in case of a crash, or pytest interferes with it.
+        # Tweak output to prevent tests with empty expected output to pass in case of a crash.
+        output.append("!!! Mypy crashed !!!")
     if returncode == 0 and not output:
         # Execute the program.
         proc = subprocess.run(

test-data/unit/pythoneval.test

@@ -1901,3 +1901,26 @@ a[x]
 _testNativeIntTypes.py:14: error: Unsupported operand types for + ("i64" and "i32")
 _testNativeIntTypes.py:15: note: Revealed type is "mypy_extensions.i64"
 _testNativeIntTypes.py:16: note: Revealed type is "mypy_extensions.i64"
+
+[case testStarUnpackNestedUnderscore]
+from typing import Tuple, Dict, List
+
+def crash() -> None:
+    d: Dict[int, Tuple[str, int, str]] = {}
+    k, (v1, *_) = next(iter(d.items()))
+
+def test1() -> None:
+    vs: List[str]
+    d: Dict[int, Tuple[str, int, int]] = {}
+    k, (v1, *vs) = next(iter(d.items()))
+    reveal_type(vs)
+
+def test2() -> None:
+    d: Dict[int, Tuple[str, int, str]] = {}
+    k, (v1, *vs) = next(iter(d.items()))
+    reveal_type(vs)
+[out]
+_testStarUnpackNestedUnderscore.py:10: error: List item 0 has incompatible type "int"; expected "str"
+_testStarUnpackNestedUnderscore.py:10: error: List item 1 has incompatible type "int"; expected "str"
+_testStarUnpackNestedUnderscore.py:11: note: Revealed type is "builtins.list[builtins.str]"
+_testStarUnpackNestedUnderscore.py:16: note: Revealed type is "builtins.list[builtins.object]"