Fix crash on malformed TypedDict in incremental mode (#16115)

Fixes #15557

FWIW I simply copy the logic for handling malformed definitions from
named tuples, that seems to be much more robust.

mypy/semanal_typeddict.py

@@ -366,7 +366,13 @@ def check_typeddict(
         name, items, types, total, tvar_defs, ok = res
         if not ok:
             # Error. Construct dummy return value.
-            info = self.build_typeddict_typeinfo("TypedDict", [], [], set(), call.line, None)
+            if var_name:
+                name = var_name
+                if is_func_scope:
+                    name += "@" + str(call.line)
+            else:
+                name = var_name = "TypedDict@" + str(call.line)
+            info = self.build_typeddict_typeinfo(name, [], [], set(), call.line, None)
         else:
             if var_name is not None and name != var_name:
                 self.fail(
@@ -395,9 +401,9 @@ def check_typeddict(
                 name, items, types, required_keys, call.line, existing_info
             )
             info.line = node.line
-            # Store generated TypeInfo under both names, see semanal_namedtuple for more details.
-            if name != var_name or is_func_scope:
-                self.api.add_symbol_skip_local(name, info)
+        # Store generated TypeInfo under both names, see semanal_namedtuple for more details.
+        if name != var_name or is_func_scope:
+            self.api.add_symbol_skip_local(name, info)
         if var_name:
             self.api.add_symbol(var_name, info, node)
         call.analyzed = TypedDictExpr(info)

test-data/unit/check-incremental.test

@@ -6479,3 +6479,28 @@ from typing_extensions import TypeVarTuple, Unpack
 Ts = TypeVarTuple("Ts")
 class C(Tuple[Unpack[Ts]]): ...
 [builtins fixtures/tuple.pyi]
+
+[case testNoIncrementalCrashOnInvalidTypedDict]
+import m
+[file m.py]
+import counts
+[file m.py.2]
+import counts
+# touch
+[file counts.py]
+from typing_extensions import TypedDict
+Counts = TypedDict("Counts", {k: int for k in "abc"})  # type: ignore
+[builtins fixtures/dict.pyi]
+
+[case testNoIncrementalCrashOnInvalidTypedDictFunc]
+import m
+[file m.py]
+import counts
+[file m.py.2]
+import counts
+# touch
+[file counts.py]
+from typing_extensions import TypedDict
+def test() -> None:
+    Counts = TypedDict("Counts", {k: int for k in "abc"})  # type: ignore
+[builtins fixtures/dict.pyi]