Fix serialization of redefined nodes

mypy/fixup.py

@@ -57,8 +57,12 @@ def visit_type_info(self, info: TypeInfo) -> None:
             if info.metaclass_type:
                 info.metaclass_type.accept(self.type_fixer)
             if info._mro_refs:
-                info.mro = [lookup_qualified_typeinfo(self.modules, name, self.allow_missing)
-                            for name in info._mro_refs]
+                # If the class is a "-redefinition", then its
+                # reference to itself might be busted, so just use the
+                # info instead of looking up the first element. Ew.
+                info.mro = [info] + [
+                    lookup_qualified_typeinfo(self.modules, name, self.allow_missing)
+                    for name in info._mro_refs[1:]]
                 info._mro_refs = None
         finally:
             self.current_info = save_info
@@ -76,6 +80,7 @@ def visit_symbol_table(self, symtab: SymbolTable) -> None:
                     stnode = lookup_qualified_stnode(self.modules, cross_ref,
                                                      self.allow_missing)
                     if stnode is not None:
+                        assert stnode.node is not None
                         value.node = stnode.node
                     elif not self.allow_missing:
                         assert stnode is not None, "Could not find cross-ref %s" % (cross_ref,)

mypy/nodes.py

@@ -2986,8 +2986,10 @@ def serialize(self, prefix: str, name: str) -> JsonDict:
             assert self.node is not None, '%s:%s' % (prefix, name)
             if prefix is not None:
                 fullname = self.node.fullname()
-                if (fullname is not None and '.' in fullname and
-                        fullname != prefix + '.' + name
+                if (fullname is not None and '.' in fullname
+                        and fullname != prefix + '.' + name
+                        # If it only doesn't match because of -redefinition, that is OK
+                        and fullname != prefix + '.' + name.split('-redefinition')[0]
                         and not (isinstance(self.node, Var)
                                  and self.node.from_module_getattr)):
                     data['cross_ref'] = fullname

mypy/semanal.py

@@ -3114,6 +3114,7 @@ def process_module_assignment(self, lvals: List[Lvalue], rval: Expression,
                         # never create module alias except on initial var definition
                         elif lval.is_inferred_def:
                             lnode.kind = self.current_symbol_kind()
+                            assert rnode.node is not None
                             lnode.node = rnode.node
 
     def process__all__(self, s: AssignmentStmt) -> None:

test-data/unit/fine-grained.test

@@ -9160,3 +9160,27 @@ Data = Tuple[User, File]
 [typing fixtures/typing-full.pyi]
 [out]
 ==
+
+[case testClassRedef]
+# An issue involved serializing these caused crashes in the past
+
+[file a.py]
+class A:
+    pass
+
+x = 0
+
+[file a.py.2]
+class A:
+    a = A()
+
+x = '0'
+
+[file b.py]
+from a import A, x
+
+class A: # type: ignore
+    pass
+
+[out]
+==