Add impl & test for fastparse2

Author: sixolet

mypy/fastparse.py

@@ -223,7 +223,7 @@ def fix_function_overloads(self, stmts: List[Statement]) -> List[Statement]:
         if len(current_overload) == 1:
             ret.append(current_overload[0])
         elif len(current_overload) > 1:
-            ret.append(OverloadedFuncDef(current_overload))
+            ret.append(OverloadedFuncDef(current_overload, None))
         return ret
 
     def in_class(self) -> bool:

mypy/fastparse2.py

@@ -18,7 +18,9 @@
 import sys
 
 from typing import Tuple, Union, TypeVar, Callable, Sequence, Optional, Any, cast, List
-from mypy.sharedparse import special_function_elide_names, argument_elide_name
+from mypy.sharedparse import (
+    special_function_elide_names, argument_elide_name, is_overload_part,
+)
 from mypy.nodes import (
     MypyFile, Node, ImportBase, Import, ImportAll, ImportFrom, FuncDef, OverloadedFuncDef,
     ClassDef, Decorator, Block, Var, OperatorAssignmentStmt,
@@ -209,19 +211,27 @@ def as_block(self, stmts: List[ast27.stmt], lineno: int) -> Block:
 
     def fix_function_overloads(self, stmts: List[Statement]) -> List[Statement]:
         ret = []  # type: List[Statement]
-        current_overload = []
+        current_overload = []  # type: List[Decorator]
         current_overload_name = None
         # mypy doesn't actually check that the decorator is literally @overload
         for stmt in stmts:
-            if isinstance(stmt, Decorator) and stmt.name() == current_overload_name:
+            if (isinstance(stmt, Decorator)
+                    and is_overload_part(stmt)
+                    and stmt.name() == current_overload_name):
                 current_overload.append(stmt)
+            elif (isinstance(stmt, FuncDef)
+                  and stmt.name() == current_overload_name
+                  and stmt.name() is not None):
+                ret.append(OverloadedFuncDef(current_overload, stmt))
+                current_overload = []
+                current_overload_name = None
             else:
                 if len(current_overload) == 1:
                     ret.append(current_overload[0])
                 elif len(current_overload) > 1:
-                    ret.append(OverloadedFuncDef(current_overload))
+                    ret.append(OverloadedFuncDef(current_overload, None))
 
-                if isinstance(stmt, Decorator):
+                if isinstance(stmt, Decorator) and is_overload_part(stmt):
                     current_overload = [stmt]
                     current_overload_name = stmt.name()
                 else:
@@ -232,7 +242,7 @@ def fix_function_overloads(self, stmts: List[Statement]) -> List[Statement]:
         if len(current_overload) == 1:
             ret.append(current_overload[0])
         elif len(current_overload) > 1:
-            ret.append(OverloadedFuncDef(current_overload))
+            ret.append(OverloadedFuncDef(current_overload, None))
         return ret
 
     def in_class(self) -> bool:

test-data/unit/check-overloading.test

@@ -20,6 +20,28 @@ class A: pass
 class B: pass
 [builtins fixtures/isinstance.pyi]
 
+[case testTypeCheckOverloadWithImplementationFastparse]
+# flags: --fast-parser
+
+from typing import overload, Any
+@overload
+def f(x: 'A') -> 'B': ...
+@overload
+def f(x: 'B') -> 'A': ...
+
+def f(x: Any) -> Any:
+   if isinstance(x, A):
+       return B()
+   else:
+       return A()
+
+reveal_type(f(A())) # E: Revealed type is '__main__.B'
+reveal_type(f(B())) # E: Revealed type is '__main__.A'
+
+class A: pass
+class B: pass
+[builtins fixtures/isinstance.pyi]
+
 [case testTypeCheckOverloadWithImplementationError]
 from typing import overload, Any