Better match narrowing for unions of type objects (#20905)

hauntsaninja · web-flow · commit 0d20e5291031 · 2026-02-27T10:15:37.000-08:00
Sequel to #20872 that has a slightly thrashy diff
diff --git a/mypy/checkpattern.py b/mypy/checkpattern.py
@@ -553,40 +553,18 @@ def visit_class_pattern(self, o: ClassPattern) -> PatternType:
         # Check class type
         #
         type_info = o.class_ref.node
-        typ = self.chk.expr_checker.accept(o.class_ref)
-        p_typ = get_proper_type(typ)
         if isinstance(type_info, TypeAlias) and not type_info.no_args:
             self.msg.fail(message_registry.CLASS_PATTERN_GENERIC_TYPE_ALIAS, o)
             return self.early_non_match()
-        elif isinstance(p_typ, FunctionLike) and p_typ.is_type_obj():
-            typ = fill_typevars_with_any(p_typ.type_object())
-            type_range = TypeRange(typ, is_upper_bound=False)
-        elif (
-            isinstance(type_info, Var)
-            and type_info.type is not None
-            and type_info.fullname == "typing.Callable"
-        ):
-            # Create a `Callable[..., Any]`
-            fallback = self.chk.named_type("builtins.function")
-            any_type = AnyType(TypeOfAny.unannotated)
-            typ = callable_with_ellipsis(any_type, ret_type=any_type, fallback=fallback)
-            type_range = TypeRange(typ, is_upper_bound=False)
-        elif isinstance(p_typ, TypeType):
-            typ = p_typ.item
-            type_range = TypeRange(p_typ.item, is_upper_bound=True)
-        elif not isinstance(p_typ, AnyType):
-            self.msg.fail(
-                message_registry.CLASS_PATTERN_TYPE_REQUIRED.format(
-                    typ.str_with_options(self.options)
-                ),
-                o,
-            )
+
+        typ = self.chk.expr_checker.accept(o.class_ref)
+        type_ranges = self.get_class_pattern_type_ranges(typ, o)
+        if type_ranges is None:
             return self.early_non_match()
-        else:
-            type_range = get_type_range(typ)
+        typ = UnionType.make_union([t.item for t in type_ranges])
 
         new_type, rest_type = self.chk.conditional_types_with_intersection(
-            current_type, [type_range], o, default=current_type
+            current_type, type_ranges, o, default=current_type
         )
         if is_uninhabited(new_type):
             return self.early_non_match()
@@ -717,6 +695,46 @@ def visit_class_pattern(self, o: ClassPattern) -> PatternType:
             new_type = UninhabitedType()
         return PatternType(new_type, rest_type, captures)
 
+    def get_class_pattern_type_ranges(self, typ: Type, o: ClassPattern) -> list[TypeRange] | None:
+        p_typ = get_proper_type(typ)
+
+        if isinstance(p_typ, UnionType):
+            type_ranges = []
+            for item in p_typ.items:
+                type_range = self.get_class_pattern_type_ranges(item, o)
+                if type_range is not None:
+                    type_ranges.extend(type_range)
+            if not type_ranges:
+                return None
+            return type_ranges
+
+        if isinstance(p_typ, FunctionLike) and p_typ.is_type_obj():
+            typ = fill_typevars_with_any(p_typ.type_object())
+            return [TypeRange(typ, is_upper_bound=False)]
+        if (
+            isinstance(o.class_ref.node, Var)
+            and o.class_ref.node.type is not None
+            and o.class_ref.node.fullname == "typing.Callable"
+        ):
+            # Create a `Callable[..., Any]`
+            fallback = self.chk.named_type("builtins.function")
+            any_type = AnyType(TypeOfAny.unannotated)
+            typ = callable_with_ellipsis(any_type, ret_type=any_type, fallback=fallback)
+            return [TypeRange(typ, is_upper_bound=False)]
+        if isinstance(p_typ, TypeType):
+            typ = p_typ.item
+            return [TypeRange(p_typ.item, is_upper_bound=True)]
+        if isinstance(p_typ, AnyType):
+            return [TypeRange(p_typ, is_upper_bound=False)]
+
+        self.msg.fail(
+            message_registry.CLASS_PATTERN_TYPE_REQUIRED.format(
+                typ.str_with_options(self.options)
+            ),
+            o,
+        )
+        return None
+
     def should_self_match(self, typ: Type) -> bool:
         typ = get_proper_type(typ)
         if isinstance(typ, TupleType):
diff --git a/test-data/unit/check-python310.test b/test-data/unit/check-python310.test
@@ -1091,13 +1091,27 @@ match m:
 [builtins fixtures/tuple.pyi]
 
 [case testMatchClassPatternIsNotType]
-a = 1
-m: object
+# flags: --strict-equality --warn-unreachable
+from typing import Any
 
-match m:
-    case a(i, j):  # E: Expected type in class pattern; found "builtins.int"
-        reveal_type(i)
-        reveal_type(j)
+def match_int(m: object, a: int):
+    match m:
+        case a(i, j):  # E: Expected type in class pattern; found "builtins.int"
+            reveal_type(i)  # E: Statement is unreachable
+            reveal_type(j)
+
+def match_int_str(m: object, a: int | str):
+    match m:
+        case a(i, j):  # E: Expected type in class pattern; found "builtins.int" \
+                       # E: Expected type in class pattern; found "builtins.str"
+            reveal_type(i)  # E: Statement is unreachable
+            reveal_type(j)
+
+def match_int_any(m: object, a: int | Any):
+    match m:
+        case a(i, j):  # E: Expected type in class pattern; found "builtins.int"
+            reveal_type(i)  # N: Revealed type is "Any"
+            reveal_type(j)  # N: Revealed type is "Any"
 
 [case testMatchClassPatternAny]
 from typing import Any
@@ -1300,15 +1314,15 @@ def f4(T: type[Example | Example2]) -> None:
 
 def f5(T: type[Example | Example2]) -> None:
     match Example("a"):
-        case T(value):  # E: Expected type in class pattern; found "type[__main__.Example] | type[__main__.Example2]"
-            reveal_type(value)  # E: Statement is unreachable
+        case T(value):
+            reveal_type(value)  # N: Revealed type is "builtins.str"
         case anything:
             reveal_type(anything)  # N: Revealed type is "__main__.Example"
 
 def f6(T: type[Example | Example2]) -> None:
     match T("a"):
-        case T(value):  # E: Expected type in class pattern; found "type[__main__.Example] | type[__main__.Example2]"
-            reveal_type(value)  # E: Statement is unreachable
+        case T(value):
+            reveal_type(value)  # N: Revealed type is "builtins.str"
         case anything:
             reveal_type(anything)  # N: Revealed type is "__main__.Example | __main__.Example2"
 
