Visit resolved forward refs by third pass type visitor (#5433)

Author: ilevkivskyi

mypy/semanal_pass3.py

@@ -700,7 +700,7 @@ def visit_instance(self, t: Instance) -> Type:
                 self.fail('Type argument "{}" of "{}" must be '
                           'a subtype of "{}"'.format(
                               arg, info.name(), tvar.upper_bound), t)
-        return t
+        return super().visit_instance(t)
 
     def check_type_var_values(self, type: TypeInfo, actuals: List[Type], arg_name: str,
                               valids: List[Type], arg_number: int, context: Context) -> None:

mypy/typeanal.py

@@ -708,28 +708,7 @@ def visit_instance(self, t: Instance) -> None:
             self.indicator['synthetic'] = True
         # Check type argument count.
         if len(t.args) != len(info.type_vars):
-            if len(t.args) == 0:
-                any_type = AnyType(TypeOfAny.from_omitted_generics,
-                                   line=t.line, column=t.column)
-                t.args = [any_type] * len(info.type_vars)
-                return
-            # Invalid number of type parameters.
-            n = len(info.type_vars)
-            s = '{} type arguments'.format(n)
-            if n == 0:
-                s = 'no type arguments'
-            elif n == 1:
-                s = '1 type argument'
-            act = str(len(t.args))
-            if act == '0':
-                act = 'none'
-            self.fail('"{}" expects {}, but {} given'.format(
-                info.name(), s, act), t)
-            # Construct the correct number of type arguments, as
-            # otherwise the type checker may crash as it expects
-            # things to be right.
-            t.args = [AnyType(TypeOfAny.from_error) for _ in info.type_vars]
-            t.invalid = True
+            fix_instance(t, self.fail)
         elif info.defn.type_vars:
             # Check type argument values. This is postponed to the end of semantic analysis
             # since we need full MROs and resolved forward references.
@@ -808,6 +787,8 @@ def visit_forwardref_type(self, t: ForwardRef) -> None:
         if t.resolved is None:
             resolved = self.anal_type(t.unbound)
             t.resolve(resolved)
+            assert t.resolved is not None
+            t.resolved.accept(self)
 
     def anal_type(self, tp: UnboundType) -> Type:
         tpan = TypeAnalyser(self.api,
@@ -824,6 +805,35 @@ def anal_type(self, tp: UnboundType) -> Type:
 TypeVarList = List[Tuple[str, TypeVarExpr]]
 
 
+def fix_instance(t: Instance, fail: Callable[[str, Context], None]) -> None:
+    """Fix a malformed instance by replacing all type arguments with Any.
+
+    Also emit a suitable error if this is not due to implicit Any's.
+    """
+    if len(t.args) == 0:
+        any_type = AnyType(TypeOfAny.from_omitted_generics,
+                           line=t.line, column=t.column)
+        t.args = [any_type] * len(t.type.type_vars)
+        return
+    # Invalid number of type parameters.
+    n = len(t.type.type_vars)
+    s = '{} type arguments'.format(n)
+    if n == 0:
+        s = 'no type arguments'
+    elif n == 1:
+        s = '1 type argument'
+    act = str(len(t.args))
+    if act == '0':
+        act = 'none'
+    fail('"{}" expects {}, but {} given'.format(
+        t.type.name(), s, act), t)
+    # Construct the correct number of type arguments, as
+    # otherwise the type checker may crash as it expects
+    # things to be right.
+    t.args = [AnyType(TypeOfAny.from_error) for _ in t.type.type_vars]
+    t.invalid = True
+
+
 def expand_type_alias(target: Type, alias_tvars: List[str], args: List[Type],
                       fail: Callable[[str, Context], None], no_args: bool, ctx: Context) -> Type:
     """Expand a (generic) type alias target following the rules outlined in TypeAlias docstring.

test-data/unit/check-classes.test

@@ -4498,3 +4498,54 @@ from typing import Any
 def __getattr__(attr: str) -> Any: ...
 [builtins fixtures/module.pyi]
 [out]
+
+[case testForwardInstanceWithWrongArgCount]
+from typing import TypeVar, Generic
+
+T = TypeVar('T')
+class G(Generic[T]): ...
+
+A = G
+x: A[B[int, int]]  # E: "G" expects 1 type argument, but 2 given
+B = G
+[out]
+
+[case testForwardInstanceWithNoArgs]
+from typing import TypeVar, Generic
+
+T = TypeVar('T')
+class G(Generic[T]): ...
+
+A = G
+x: A[B]
+reveal_type(x)  # E: Revealed type is '__main__.G[__main__.G[Any]]'
+B = G
+[out]
+
+[case testForwardInstanceWithBound]
+from typing import TypeVar, Generic
+
+T = TypeVar('T', bound=str)
+class G(Generic[T]): ...
+
+A = G
+x: A[B[int]]
+B = G
+[out]
+main:7: error: Type argument "builtins.int" of "G" must be a subtype of "builtins.str"
+main:7: error: Type argument "__main__.G[builtins.int]" of "G" must be a subtype of "builtins.str"
+
+[case testExtremeForwardReferencing]
+from typing import TypeVar, Generic
+
+T = TypeVar('T')
+class B(Generic[T]): ...
+
+y: A
+z: A[int]
+x = [y, z]
+reveal_type(x)  # E: Revealed type is 'builtins.list[__main__.B*[Any]]'
+
+A = B
+[builtins fixtures/list.pyi]
+[out]

test-data/unit/pythoneval.test

@@ -1306,3 +1306,14 @@ def print_custom_table() -> None:
         reveal_type(row)
 [out]
 _testLoadsOfOverloads.py:24: error: Revealed type is 'builtins.str*'
+
+[case testReduceWithAnyInstance]
+from typing import Iterable
+from functools import reduce
+M = Iterable
+def f(m1: M, m2):
+    ...
+def g(ms: 'T[M]') -> None:
+    reduce(f, ms)
+T = Iterable
+[out]