From f1e380d5bfe632cde08c5cad8f2613c26e7d0e8b Mon Sep 17 00:00:00 2001
From: Marc Mueller <30130371+cdce8p@users.noreply.github.com>
Date: Fri, 27 Dec 2024 00:59:29 +0100
Subject: [PATCH] Add NoMatch for invalid signatures in overloads

---
 mypy/checkexpr.py                             | 10 ++++++++++
 mypy/typeanal.py                              | 18 +++++++++++++++++-
 mypy/types.py                                 |  4 ++++
 mypy/typeshed/stdlib/typing_extensions.pyi    |  2 ++
 test-data/unit/check-overloading.test         | 18 ++++++++++++++++++
 test-data/unit/lib-stub/typing_extensions.pyi |  2 ++
 6 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index 964149fa8df4..52f60d124393 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -1485,6 +1485,16 @@ def check_call_expr_with_callee_type(
         proper_callee = get_proper_type(callee_type)
         if isinstance(e.callee, (NameExpr, MemberExpr)):
             self.chk.warn_deprecated_overload_item(e.callee.node, e, target=callee_type)
+        if (
+            isinstance((p_type := get_proper_type(ret_type)), AnyType)
+            and p_type.type_of_any == TypeOfAny.no_match
+            and isinstance(proper_callee, CallableType)
+        ):
+            self.chk.fail(
+                f'No matching overload found for "{proper_callee.name}"',
+                context=e,
+                code=codes.CALL_OVERLOAD,
+            )
         if isinstance(e.callee, RefExpr) and isinstance(proper_callee, CallableType):
             # Cache it for find_isinstance_check()
             if proper_callee.type_guard is not None:
diff --git a/mypy/typeanal.py b/mypy/typeanal.py
index 751ed85ea6f3..a4ae46722d7c 100644
--- a/mypy/typeanal.py
+++ b/mypy/typeanal.py
@@ -65,6 +65,7 @@
     FINAL_TYPE_NAMES,
     LITERAL_TYPE_NAMES,
     NEVER_NAMES,
+    NO_MATCH_NAMES,
     TYPE_ALIAS_NAMES,
     AnyType,
     BoolTypeQuery,
@@ -227,6 +228,7 @@ def __init__(
         allow_typed_dict_special_forms: bool = False,
         allow_param_spec_literals: bool = False,
         allow_unpack: bool = False,
+        allow_no_match: bool = False,
         report_invalid_types: bool = True,
         prohibit_self_type: str | None = None,
         prohibit_special_class_field_types: str | None = None,
@@ -282,6 +284,7 @@ def __init__(
         self.allow_type_any = allow_type_any
         self.allow_type_var_tuple = False
         self.allow_unpack = allow_unpack
+        self.allow_no_match = allow_no_match
 
     def lookup_qualified(
         self, name: str, ctx: Context, suppress_errors: bool = False
@@ -694,6 +697,15 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Typ
             return self.anal_type(t.args[0])
         elif fullname in NEVER_NAMES:
             return UninhabitedType()
+        elif fullname in NO_MATCH_NAMES:
+            if not self.allow_no_match:
+                self.fail(
+                    "NoMatch can only be used as an overload return annotation",
+                    t,
+                    code=codes.VALID_TYPE,
+                )
+                return AnyType(TypeOfAny.from_error)
+            return AnyType(TypeOfAny.no_match)
         elif fullname in LITERAL_TYPE_NAMES:
             return self.analyze_literal_type(t)
         elif fullname in ANNOTATED_TYPE_NAMES:
@@ -1158,7 +1170,7 @@ def visit_callable_type(
                 arg_types=arg_types,
                 arg_kinds=arg_kinds,
                 arg_names=arg_names,
-                ret_type=self.anal_type(t.ret_type, nested=nested),
+                ret_type=self.anal_type(t.ret_type, nested=nested, allow_no_match=True),
                 # If the fallback isn't filled in yet,
                 # its type will be the falsey FakeInfo
                 fallback=(t.fallback if t.fallback.type else self.named_type("builtins.function")),
@@ -1877,6 +1889,7 @@ def anal_type(
         allow_unpack: bool = False,
         allow_ellipsis: bool = False,
         allow_typed_dict_special_forms: bool = False,
+        allow_no_match: bool = False,
     ) -> Type:
         if nested:
             self.nesting_level += 1
@@ -1886,6 +1899,8 @@ def anal_type(
         self.allow_ellipsis = allow_ellipsis
         old_allow_unpack = self.allow_unpack
         self.allow_unpack = allow_unpack
+        old_no_match = self.allow_no_match
+        self.allow_no_match = allow_no_match
         try:
             analyzed = t.accept(self)
         finally:
@@ -1894,6 +1909,7 @@ def anal_type(
             self.allow_typed_dict_special_forms = old_allow_typed_dict_special_forms
             self.allow_ellipsis = old_allow_ellipsis
             self.allow_unpack = old_allow_unpack
+            self.allow_no_match = old_no_match
         if (
             not allow_param_spec
             and isinstance(analyzed, ParamSpecType)
diff --git a/mypy/types.py b/mypy/types.py
index e92ab0889991..76a1b1a40d7f 100644
--- a/mypy/types.py
+++ b/mypy/types.py
@@ -173,6 +173,8 @@
 # Supported @override decorator names.
 OVERRIDE_DECORATOR_NAMES: Final = ("typing.override", "typing_extensions.override")
 
+NO_MATCH_NAMES: Final = ("typing.NoMatch", "typing_extensions.NoMatch")
+
 # A placeholder used for Bogus[...] parameters
 _dummy: Final[Any] = object()
 
@@ -209,6 +211,8 @@ class TypeOfAny:
     # used to ignore Anys inserted by the suggestion engine when
     # generating constraints.
     suggestion_engine: Final = 9
+    # Does this Any come from NoMatch overload return annotation?
+    no_match: Final = 10
 
 
 def deserialize_type(data: JsonDict | str) -> Type:
diff --git a/mypy/typeshed/stdlib/typing_extensions.pyi b/mypy/typeshed/stdlib/typing_extensions.pyi
index a6b606e6b670..d6199a809c91 100644
--- a/mypy/typeshed/stdlib/typing_extensions.pyi
+++ b/mypy/typeshed/stdlib/typing_extensions.pyi
@@ -529,6 +529,8 @@ else:
     ReadOnly: _SpecialForm
     TypeIs: _SpecialForm
 
+NoMatch: _SpecialForm
+
 class Doc:
     documentation: str
     def __init__(self, documentation: str, /) -> None: ...
diff --git a/test-data/unit/check-overloading.test b/test-data/unit/check-overloading.test
index 9d01ce6bd480..b7d4a92342e4 100644
--- a/test-data/unit/check-overloading.test
+++ b/test-data/unit/check-overloading.test
@@ -6768,3 +6768,21 @@ class D(Generic[T]):
 a: D[str]  # E: Type argument "str" of "D" must be a subtype of "C"
 reveal_type(a.f(1))  # N: Revealed type is "builtins.int"
 reveal_type(a.f("x"))  # N: Revealed type is "builtins.str"
+
+[case testOverloadNoMatch]
+from typing import Sequence, overload
+from typing_extensions import NoMatch
+
+@overload
+def f1(args: str) -> NoMatch: ...
+@overload
+def f1(arg: Sequence[str]) -> int: ...
+def f1(arg): ...
+
+reveal_type(f1(["Hello", "World"]))  # N: Revealed type is "builtins.int"
+reveal_type(f1("Hello World"))  # E: No matching overload found for "f1" \
+                                # N: Revealed type is "Any"
+
+y: NoMatch  # E: NoMatch can only be used as an overload return annotation
+def f2(arg: NoMatch) -> int: ...  # E: NoMatch can only be used as an overload return annotation
+[builtins fixtures/tuple.pyi]
diff --git a/test-data/unit/lib-stub/typing_extensions.pyi b/test-data/unit/lib-stub/typing_extensions.pyi
index cb054b0e6b4f..998233f1e63b 100644
--- a/test-data/unit/lib-stub/typing_extensions.pyi
+++ b/test-data/unit/lib-stub/typing_extensions.pyi
@@ -45,6 +45,8 @@ ReadOnly: _SpecialForm
 
 Self: _SpecialForm
 
+NoMatch: _SpecialForm
+
 @final
 class TypeAliasType:
     def __init__(