[red-knot] Add typing.Any as a spelling for the Any type

crates/red_knot_python_semantic/resources/mdtest/annotations/any.md

@@ -0,0 +1,74 @@
+# Any
+
+## Annotation
+
+`typing.Any` is a way to name the Any type.
+
+```py
+from typing import Any
+
+x: Any = 1
+x = "foo"
+
+def f():
+    reveal_type(x)  # revealed: Any
+```
+
+## Aliased to a different name
+
+If you alias `typing.Any` to another name, we still recognize that as a spelling of the Any type.
+
+```py
+from typing import Any as RenamedAny
+
+x: RenamedAny = 1
+x = "foo"
+
+def f():
+    reveal_type(x)  # revealed: Any
+```
+
+## Shadowed class
+
+If you define your own class named `Any`, using that in a type expression refers to your class, and
+isn't a spelling of the Any type.
+
+```py
+class Any:
+    pass
+
+x: Any
+
+def f():
+    reveal_type(x)  # revealed: Any
+
+# This verifies that we're not accidentally seeing typing.Any, since str is assignable
+# to that but not to our locally defined class.
+y: Any = "not an Any"  # error: [invalid-assignment]
+```
+
+## Subclass
+
+The spec allows you to define subclasses of `Any`, which must also resolve to the Any type.
+
+TODO: Handle assignments correctly. `Subclass` has an unknown superclass, which might be `int`. The
+assignment to `x` should not be allowed, even when the unknown superclass is `int`. The assignment
+to `y` should be allowed, since `Subclass` might have `int` as a superclass, and is therefore
+assignable to `int`.
+
+```py
+from typing import Any
+
+class Subclass(Any):
+    pass
+
+reveal_type(Subclass.__mro__)  # revealed: tuple[Literal[Subclass], Any, Literal[object]]
+
+x: Subclass = 1  # error: [invalid-assignment]
+y: int = Subclass()  # error: [invalid-assignment]
+
+def f() -> Subclass:
+    pass
+
+reveal_type(f())  # revealed: Subclass
+```

crates/red_knot_python_semantic/src/types.rs

@@ -1560,6 +1560,7 @@ impl<'db> Type<'db> {
                 Type::Never
             }
             Type::KnownInstance(KnownInstanceType::LiteralString) => Type::LiteralString,
+            Type::KnownInstance(KnownInstanceType::Any) => Type::Any,
             _ => todo_type!(),
         }
     }
@@ -1902,6 +1903,8 @@ pub enum KnownInstanceType<'db> {
     NoReturn,
     /// The symbol `typing.Never` available since 3.11 (which can also be found as `typing_extensions.Never`)
     Never,
+    /// The symbol `typing.Any` (which can also be found as `typing_extensions.Any`)
+    Any,
     /// A single instance of `typing.TypeVar`
     TypeVar(TypeVarInstance<'db>),
     /// A single instance of `typing.TypeAliasType` (PEP 695 type alias)
@@ -1919,6 +1922,7 @@ impl<'db> KnownInstanceType<'db> {
             Self::TypeVar(_) => "TypeVar",
             Self::NoReturn => "NoReturn",
             Self::Never => "Never",
+            Self::Any => "Any",
             Self::TypeAliasType(_) => "TypeAliasType",
         }
     }
@@ -1933,6 +1937,7 @@ impl<'db> KnownInstanceType<'db> {
             | Self::Union
             | Self::NoReturn
             | Self::Never
+            | Self::Any
             | Self::TypeAliasType(_) => Truthiness::AlwaysTrue,
         }
     }
@@ -1946,6 +1951,7 @@ impl<'db> KnownInstanceType<'db> {
             Self::Union => "typing.Union",
             Self::NoReturn => "typing.NoReturn",
             Self::Never => "typing.Never",
+            Self::Any => "typing.Any",
             Self::TypeVar(typevar) => typevar.name(db),
             Self::TypeAliasType(_) => "typing.TypeAliasType",
         }
@@ -1960,6 +1966,7 @@ impl<'db> KnownInstanceType<'db> {
             Self::Union => KnownClass::SpecialForm,
             Self::NoReturn => KnownClass::SpecialForm,
             Self::Never => KnownClass::SpecialForm,
+            Self::Any => KnownClass::Object,
             Self::TypeVar(_) => KnownClass::TypeVar,
             Self::TypeAliasType(_) => KnownClass::TypeAliasType,
         }
@@ -1979,6 +1986,7 @@ impl<'db> KnownInstanceType<'db> {
             return None;
         }
         match (module.name().as_str(), instance_name) {
+            ("typing", "Any") => Some(Self::Any),
             ("typing" | "typing_extensions", "Literal") => Some(Self::Literal),
             ("typing" | "typing_extensions", "LiteralString") => Some(Self::LiteralString),
             ("typing" | "typing_extensions", "Optional") => Some(Self::Optional),
@@ -2647,7 +2655,11 @@ impl<'db> Class<'db> {
     pub fn is_subclass_of(self, db: &'db dyn Db, other: Class) -> bool {
         // `is_subclass_of` is checking the subtype relation, in which gradual types do not
         // participate, so we should not return `True` if we find `Any/Unknown` in the MRO.
-        self.iter_mro(db).contains(&ClassBase::Class(other))
+        self.is_subclass_of_base(db, other)
+    }
+
+    fn is_subclass_of_base(self, db: &'db dyn Db, other: impl Into<ClassBase<'db>>) -> bool {
+        self.iter_mro(db).contains(&other.into())
     }
 
     /// Return the explicit `metaclass` of this class, if one is defined.

crates/red_knot_python_semantic/src/types/infer.rs

@@ -1660,7 +1660,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         let value_ty = self.expression_ty(value);
         let name_ast_id = name.scoped_expression_id(self.db, self.scope());
 
-        let target_ty = match assignment.target() {
+        let mut target_ty = match assignment.target() {
             TargetKind::Sequence(unpack) => {
                 let unpacked = infer_unpack_types(self.db, unpack);
                 // Only copy the diagnostics if this is the first assignment to avoid duplicating the
@@ -1674,6 +1674,13 @@ impl<'db> TypeInferenceBuilder<'db> {
             TargetKind::Name => value_ty,
         };
 
+        if let Some(known_instance) = file_to_module(self.db, definition.file(self.db))
+            .as_ref()
+            .and_then(|module| KnownInstanceType::try_from_module_and_symbol(module, &name.id))
+        {
+            target_ty = Type::KnownInstance(known_instance);
+        }
+
         self.store_expression_type(name, target_ty);
         self.add_binding(name.into(), definition, target_ty);
     }
@@ -4653,6 +4660,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                 );
                 Type::Unknown
             }
+            KnownInstanceType::Any => Type::Any,
         }
     }
 

crates/red_knot_python_semantic/src/types/mro.rs

@@ -379,6 +379,7 @@ impl<'db> ClassBase<'db> {
                 | KnownInstanceType::NoReturn
                 | KnownInstanceType::Never
                 | KnownInstanceType::Optional => None,
+                KnownInstanceType::Any => Some(Self::Any),
             },
         }
     }
@@ -406,6 +407,12 @@ impl<'db> ClassBase<'db> {
     }
 }
 
+impl<'db> From<Class<'db>> for ClassBase<'db> {
+    fn from(value: Class<'db>) -> Self {
+        ClassBase::Class(value)
+    }
+}
+
 impl<'db> From<ClassBase<'db>> for Type<'db> {
     fn from(value: ClassBase<'db>) -> Self {
         match value {