Do not union when encountering a declared attribute

Author: sharkdp

crates/ty_python_semantic/resources/mdtest/attributes.md

@@ -891,7 +891,7 @@ reveal_type(Derived().redeclared_with_same_type)  # revealed: str | None
 
 # TODO: It would probably be more consistent if these were `str | None`
 reveal_type(Derived.redeclared_with_narrower_type)  # revealed: str
-reveal_type(Derived().redeclared_with_narrower_type)  # revealed: str | None
+reveal_type(Derived().redeclared_with_narrower_type)  # revealed: str
 
 # TODO: It would probably be more consistent if these were `str | None`
 reveal_type(Derived.redeclared_with_wider_type)  # revealed: str | int | None
@@ -915,7 +915,7 @@ reveal_type(Derived().pure_overwritten_in_subclass_method)  # revealed: str
 reveal_type(Derived.undeclared)  # revealed: Unknown | Literal["intermediate"]
 reveal_type(Derived().undeclared)  # revealed: Unknown | Literal["intermediate"]
 
-reveal_type(Derived().pure_undeclared)  # revealed: Unknown | Literal["base", "intermediate"]
+reveal_type(Derived().pure_undeclared)  # revealed: Unknown | Literal["intermediate", "base"]
 ```
 
 ## Accessing attributes on class objects

crates/ty_python_semantic/src/types/class.rs

@@ -113,10 +113,7 @@ fn implicit_attribute_initial<'db>(
     _name: String,
     _target_method_decorator: MethodDecorator,
 ) -> Member<'db> {
-    Member {
-        inner: Place::Unbound.into(),
-        is_declared: false,
-    }
+    Member::unbound()
 }
 
 fn try_mro_cycle_recover<'db>(
@@ -2873,10 +2870,7 @@ impl<'db> ClassLiteral<'db> {
         let mut union_qualifiers = TypeQualifiers::empty();
         let mut is_definitely_bound = false;
 
-        let mro = self.try_mro(db, specialization);
-        let mro = mro.unwrap_or_else(|e| e.fallback_mro());
-
-        for superclass in mro.iter().rev() {
+        for superclass in self.iter_mro(db, specialization) {
             match superclass {
                 ClassBase::Generic | ClassBase::Protocol => {
                     // Skip over these very special class bases that aren't really classes.
@@ -2903,13 +2897,7 @@ impl<'db> ClassLiteral<'db> {
                             is_definitely_bound = true;
 
                             if is_declared {
-                                if union.is_empty() {
-                                    // Short-circuit, no need to allocate inside the union builder
-                                    return member;
-                                }
-
-                                return Place::bound(union.add(ty).build())
-                                    .with_qualifiers(union_qualifiers);
+                                return member;
                             }
                         }