Allow Any to match sequence patterns

Author: sterliakov

mypy/checkpattern.py

@@ -713,6 +713,8 @@ def should_self_match(self, typ: Type) -> bool:
         return False
 
     def can_match_sequence(self, typ: ProperType) -> bool:
+        if isinstance(typ, AnyType):
+            return True
         if isinstance(typ, UnionType):
             return any(self.can_match_sequence(get_proper_type(item)) for item in typ.items)
         for other in self.non_sequence_match_types:
@@ -763,6 +765,8 @@ def construct_sequence_child(self, outer_type: Type, inner_type: Type) -> Type:
         or class T(Sequence[Tuple[T, T]]), there is no way any of those can map to Sequence[str].
         """
         proper_type = get_proper_type(outer_type)
+        if isinstance(proper_type, AnyType):
+            return outer_type
         if isinstance(proper_type, UnionType):
             types = [
                 self.construct_sequence_child(item, inner_type)
@@ -772,7 +776,6 @@ def construct_sequence_child(self, outer_type: Type, inner_type: Type) -> Type:
             return make_simplified_union(types)
         sequence = self.chk.named_generic_type("typing.Sequence", [inner_type])
         if is_subtype(outer_type, self.chk.named_type("typing.Sequence")):
-            proper_type = get_proper_type(outer_type)
             if isinstance(proper_type, TupleType):
                 proper_type = tuple_fallback(proper_type)
             assert isinstance(proper_type, Instance)

test-data/unit/check-python310.test

@@ -2439,3 +2439,35 @@ def foo(x: T) -> T:
     return out
 
 [builtins fixtures/isinstance.pyi]
+
+[case testMatchSequenceReachableFromAny]
+# flags: --warn-unreachable
+from typing import Any
+
+def maybe_list(d: Any) -> int:
+    match d:
+        case []:
+            return 0
+        case [[_]]:
+            return 1
+        case [_]:
+            return 1
+        case _:
+            return 2
+
+def with_guard(d: Any) -> None:
+    match d:
+        case [s] if isinstance(s, str):
+            reveal_type(s)  # N: Revealed type is "builtins.str"
+    match d:
+        case (s,) if isinstance(s, str):
+            reveal_type(s)  # N: Revealed type is "builtins.str"
+
+def nested_in_dict(d: dict[str, Any]) -> int:
+    match d:
+        case {"src": ["src"]}:
+            return 1
+        case _:
+            return 0
+
+[builtins fixtures/dict.pyi]