Fix forward reference in type alias bound

python · May 15, 2024 · 4819d60 · 4819d60
1 parent ef1b473
commit 4819d60
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Showing 2 changed files with 8 additions and 2 deletions.
diff --git a/mypy/semanal.py b/mypy/semanal.py
@@ -5219,8 +5219,9 @@ def visit_match_stmt(self, s: MatchStmt) -> None:
     def visit_type_alias_stmt(self, s: TypeAliasStmt) -> None:
         self.statement = s
         type_params = self.push_type_args(s.type_args, s)
-        # TODO: defer as needed
-        assert type_params is not None, "forward references in type aliases not implemented"
+        if type_params is None:
+            self.defer(s)
+            return
         all_type_params_names = [p.name for p in s.type_args]
 
         try:

diff --git a/test-data/unit/check-python312.test b/test-data/unit/check-python312.test
@@ -586,6 +586,11 @@ type B = int + str  # E: Invalid type alias: expression is not a valid type
 b: B
 reveal_type(b)  # N: Revealed type is "Any"
 
+[case testPEP695TypeAliasBoundForwardReference]
+# mypy: enable-incomplete-feature=NewGenericSyntax
+type B[T: Foo] = list[T]
+class Foo: pass
+
 [case testPEP695UpperBound]
 # flags: --enable-incomplete-feature=NewGenericSyntax