Rollup merge of #152926 - makai410:final-on-assoc-type, r=fmease

Fix ICE when an associated type is wrongly marked as `final`

Fixes: #152797.

cc @mu001999 .

Author: JonathanBrouwer

compiler/rustc_ast_lowering/src/item.rs

@@ -1085,9 +1085,18 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }
         };
 
-        let (defaultness, _) = self.lower_defaultness(i.kind.defaultness(), has_value, || {
-            hir::Defaultness::Default { has_value }
-        });
+        let defaultness = match i.kind.defaultness() {
+            // We do not yet support `final` on trait associated items other than functions.
+            // Even though we reject `final` on non-functions during AST validation, we still
+            // need to stop propagating it here because later compiler passes do not expect
+            // and cannot handle such items.
+            Defaultness::Final(..) if !matches!(i.kind, AssocItemKind::Fn(..)) => {
+                Defaultness::Implicit
+            }
+            defaultness => defaultness,
+        };
+        let (defaultness, _) = self
+            .lower_defaultness(defaultness, has_value, || hir::Defaultness::Default { has_value });
 
         let item = hir::TraitItem {
             owner_id: trait_item_def_id,

tests/ui/traits/final/final-on-assoc-type-const.rs

@@ -0,0 +1,12 @@
+// This is a regression test for <https://github.com/rust-lang/rust/issues/152797>.
+#![feature(final_associated_functions)]
+#![feature(min_generic_const_args)]
+#![expect(incomplete_features)]
+trait Uwu {
+    final type Ovo;
+    //~^ error: `final` is only allowed on associated functions in traits
+    final type const QwQ: ();
+    //~^ error: `final` is only allowed on associated functions in traits
+}
+
+fn main() {}

tests/ui/traits/final/final-on-assoc-type-const.stderr

@@ -0,0 +1,18 @@
+error: `final` is only allowed on associated functions in traits
+  --> $DIR/final-on-assoc-type-const.rs:6:5
+   |
+LL |     final type Ovo;
+   |     -----^^^^^^^^^^
+   |     |
+   |     `final` because of this
+
+error: `final` is only allowed on associated functions in traits
+  --> $DIR/final-on-assoc-type-const.rs:8:5
+   |
+LL |     final type const QwQ: ();
+   |     -----^^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     `final` because of this
+
+error: aborting due to 2 previous errors
+

tests/ui/traits/final/positions.rs

@@ -38,11 +38,9 @@ final impl Trait for Foo {
 
     final type Foo = ();
     //~^ ERROR `final` is only allowed on associated functions in traits
-    //~^^ ERROR cannot override `Foo` because it already has a `final` definition in the trait
 
     final const FOO: usize = 1;
     //~^ ERROR `final` is only allowed on associated functions in traits
-    //~^^ ERROR cannot override `FOO` because it already has a `final` definition in the trait
 }
 
 

tests/ui/traits/final/positions.stderr

@@ -15,15 +15,15 @@ LL | final trait Trait {
    = note: only associated functions in traits can be `final`
 
 error: a static item cannot be `final`
-  --> $DIR/positions.rs:67:5
+  --> $DIR/positions.rs:65:5
    |
 LL |     final static FOO_EXTERN: usize = 0;
    |     ^^^^^ `final` because of this
    |
    = note: only associated functions in traits can be `final`
 
 error: an extern block cannot be `final`
-  --> $DIR/positions.rs:58:1
+  --> $DIR/positions.rs:56:1
    |
 LL | final unsafe extern "C" {
    | ^^^^^ `final` because of this
@@ -87,55 +87,55 @@ LL |     final type Foo = ();
    |     `final` because of this
 
 error: `final` is only allowed on associated functions in traits
-  --> $DIR/positions.rs:43:5
+  --> $DIR/positions.rs:42:5
    |
 LL |     final const FOO: usize = 1;
    |     -----^^^^^^^^^^^^^^^^^^^^^^
    |     |
    |     `final` because of this
 
 error: `final` is only allowed on associated functions in traits
-  --> $DIR/positions.rs:49:1
+  --> $DIR/positions.rs:47:1
    |
 LL | final fn foo() {}
    | -----^^^^^^^^^
    | |
    | `final` because of this
 
 error: `final` is only allowed on associated functions in traits
-  --> $DIR/positions.rs:52:1
+  --> $DIR/positions.rs:50:1
    |
 LL | final type FooTy = ();
    | -----^^^^^^^^^^^^^^^^^
    | |
    | `final` because of this
 
 error: `final` is only allowed on associated functions in traits
-  --> $DIR/positions.rs:55:1
+  --> $DIR/positions.rs:53:1
    |
 LL | final const FOO: usize = 0;
    | -----^^^^^^^^^^^^^^^^^^^^^^
    | |
    | `final` because of this
 
 error: `final` is only allowed on associated functions in traits
-  --> $DIR/positions.rs:61:5
+  --> $DIR/positions.rs:59:5
    |
 LL |     final fn foo_extern();
    |     -----^^^^^^^^^^^^^^^^^
    |     |
    |     `final` because of this
 
 error: `final` is only allowed on associated functions in traits
-  --> $DIR/positions.rs:64:5
+  --> $DIR/positions.rs:62:5
    |
 LL |     final type FooExtern;
    |     -----^^^^^^^^^^^^^^^^
    |     |
    |     `final` because of this
 
 error: incorrect `static` inside `extern` block
-  --> $DIR/positions.rs:67:18
+  --> $DIR/positions.rs:65:18
    |
 LL | final unsafe extern "C" {
    | ----------------------- `extern` blocks define existing foreign statics and statics inside of them cannot have a body
@@ -159,29 +159,5 @@ note: `method` is marked final here
 LL |     final fn method() {}
    |     ^^^^^^^^^^^^^^^^^
 
-error: cannot override `Foo` because it already has a `final` definition in the trait
-  --> $DIR/positions.rs:39:5
-   |
-LL |     final type Foo = ();
-   |     ^^^^^^^^^^^^^^
-   |
-note: `Foo` is marked final here
-  --> $DIR/positions.rs:16:5
-   |
-LL |     final type Foo = ();
-   |     ^^^^^^^^^^^^^^
-
-error: cannot override `FOO` because it already has a `final` definition in the trait
-  --> $DIR/positions.rs:43:5
-   |
-LL |     final const FOO: usize = 1;
-   |     ^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: `FOO` is marked final here
-  --> $DIR/positions.rs:19:5
-   |
-LL |     final const FOO: usize = 1;
-   |     ^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 21 previous errors
+error: aborting due to 19 previous errors