Fix previous partial fix (#17429)

This is a bit unfortunate, but the best we can probably do.

cc @hauntsaninja

Author: ilevkivskyi

mypy/plugins/functools.py

@@ -137,6 +137,20 @@ def partial_new_callback(ctx: mypy.plugin.FunctionContext) -> Type:
     # We must normalize from the start to have coherent view together with TypeChecker.
     fn_type = fn_type.with_unpacked_kwargs().with_normalized_var_args()
 
+    last_context = ctx.api.type_context[-1]
+    if not fn_type.is_type_obj():
+        # We wrap the return type to get use of a possible type context provided by caller.
+        # We cannot do this in case of class objects, since otherwise the plugin may get
+        # falsely triggered when evaluating the constructed call itself.
+        ret_type: Type = ctx.api.named_generic_type(PARTIAL, [fn_type.ret_type])
+        wrapped_return = True
+    else:
+        ret_type = fn_type.ret_type
+        # Instead, for class objects we ignore any type context to avoid spurious errors,
+        # since the type context will be partial[X] etc., not X.
+        ctx.api.type_context[-1] = None
+        wrapped_return = False
+
     defaulted = fn_type.copy_modified(
         arg_kinds=[
             (
@@ -146,7 +160,7 @@ def partial_new_callback(ctx: mypy.plugin.FunctionContext) -> Type:
             )
             for k in fn_type.arg_kinds
         ],
-        ret_type=ctx.api.named_generic_type(PARTIAL, [fn_type.ret_type]),
+        ret_type=ret_type,
     )
     if defaulted.line < 0:
         # Make up a line number if we don't have one
@@ -189,16 +203,20 @@ def partial_new_callback(ctx: mypy.plugin.FunctionContext) -> Type:
         arg_names=actual_arg_names,
         context=call_expr,
     )
+    if not wrapped_return:
+        # Restore previously ignored context.
+        ctx.api.type_context[-1] = last_context
+
     bound = get_proper_type(bound)
     if not isinstance(bound, CallableType):
         return ctx.default_return_type
-    wrapped_ret_type = get_proper_type(bound.ret_type)
-    if not isinstance(wrapped_ret_type, Instance) or wrapped_ret_type.type.fullname != PARTIAL:
-        return ctx.default_return_type
-    if not mypy.semanal.refers_to_fullname(ctx.args[0][0], PARTIAL):
-        # If the first argument is partial, above call will trigger the plugin
-        # again, in between the wrapping above an unwrapping here.
-        bound = bound.copy_modified(ret_type=wrapped_ret_type.args[0])
+
+    if wrapped_return:
+        # Reverse the wrapping we did above.
+        ret_type = get_proper_type(bound.ret_type)
+        if not isinstance(ret_type, Instance) or ret_type.type.fullname != PARTIAL:
+            return ctx.default_return_type
+        bound = bound.copy_modified(ret_type=ret_type.args[0])
 
     formal_to_actual = map_actuals_to_formals(
         actual_kinds=actual_arg_kinds,

test-data/unit/check-functools.test

@@ -455,3 +455,16 @@ first_kw([1])  # E: Too many positional arguments for "get" \
                # E: Too few arguments for "get" \
                # E: Argument 1 to "get" has incompatible type "List[int]"; expected "int"
 [builtins fixtures/list.pyi]
+
+[case testFunctoolsPartialClassObjectMatchingPartial]
+from functools import partial
+
+class A:
+    def __init__(self, var: int, b: int, c: int) -> None: ...
+
+p = partial(A, 1)
+reveal_type(p)  # N: Revealed type is "functools.partial[__main__.A]"
+p(1, "no")  # E: Argument 2 to "A" has incompatible type "str"; expected "int"
+
+q: partial[A] = partial(A, 1)  # OK
+[builtins fixtures/tuple.pyi]