Rollup merge of rust-lang#144291 - oli-obk:const_trait_alias, r=fee1-dead

Constify trait aliases

Allow `const trait Foo = Bar + [const] Baz;` trait alias declarations. Their rules are the same as with super traits of const traits. So `[const] Baz` or `const Baz` is only required for `[const] Foo` or `const Foo` bounds respectively.

tracking issue rust-lang#41517 (part of the general trait alias feature gate, but I can split it out into a separate const trait alias feature gate. I just assumed that const traits would stabilize before trait aliases, and we'd want to stabilize trait aliases together with const trait aliases at the same time)

r? ``@compiler-errors`` ``@fee1-dead``

Author: matthiaskrgr

clippy_lints/src/item_name_repetitions.rs

@@ -528,7 +528,7 @@ impl LateLintPass<'_> for ItemNameRepetitions {
             | ItemKind::Macro(ident, ..)
             | ItemKind::Static(_, ident, ..)
             | ItemKind::Trait(_, _, _, ident, ..)
-            | ItemKind::TraitAlias(ident, ..)
+            | ItemKind::TraitAlias(_, ident, ..)
             | ItemKind::TyAlias(ident, ..)
             | ItemKind::Union(ident, ..)
             | ItemKind::Use(_, UseKind::Single(ident)) => ident,

clippy_utils/src/ast_utils/mod.rs

@@ -473,8 +473,24 @@ pub fn eq_item_kind(l: &ItemKind, r: &ItemKind) -> bool {
                 && over(lb, rb, eq_generic_bound)
                 && over(lis, ris, |l, r| eq_item(l, r, eq_assoc_item_kind))
         },
-        (TraitAlias(li, lg, lb), TraitAlias(ri, rg, rb)) => {
-            eq_id(*li, *ri) && eq_generics(lg, rg) && over(lb, rb, eq_generic_bound)
+        (
+            TraitAlias(box ast::TraitAlias {
+                ident: li,
+                generics: lg,
+                bounds: lb,
+                constness: lc,
+            }),
+            TraitAlias(box ast::TraitAlias {
+                ident: ri,
+                generics: rg,
+                bounds: rb,
+                constness: rc,
+            }),
+        ) => {
+            matches!(lc, ast::Const::No) == matches!(rc, ast::Const::No)
+                && eq_id(*li, *ri)
+                && eq_generics(lg, rg)
+                && over(lb, rb, eq_generic_bound)
         },
         (
             Impl(ast::Impl {