Auto merge of #90207 - BoxyUwU:stabilise_cg_defaults, r=lcnr

Stabilise `feature(const_generics_defaults)`

`feature(const_generics_defaults)` is complete implementation wise and has a pretty extensive test suite so I think is ready for stabilisation.

needs stabilisation report and maybe an RFC :sweat_smile:

r? `@lcnr`
cc `@rust-lang/project-const-generics`

1 files changed, 3 insertions, 14 deletions

diff --git a/compiler/rustc_parse/src/parser/generics.rs b/compiler/rustc_parse/src/parser/generics.rs
index 07887a7a59c..419ea9cced0 100644
--- a/compiler/rustc_parse/src/parser/generics.rs
+++ b/compiler/rustc_parse/src/parser/generics.rs
@@ -5,7 +5,7 @@ use rustc_ast::{
     self as ast, Attribute, GenericBounds, GenericParam, GenericParamKind, WhereClause,
 };
 use rustc_errors::PResult;
-use rustc_span::symbol::{kw, sym};
+use rustc_span::symbol::kw;
 
 impl<'a> Parser<'a> {
     /// Parses bounds of a lifetime parameter `BOUND + BOUND + BOUND`, possibly with trailing `+`.
@@ -59,19 +59,8 @@ impl<'a> Parser<'a> {
         self.expect(&token::Colon)?;
         let ty = self.parse_ty()?;
 
-        // Parse optional const generics default value, taking care of feature gating the spans
-        // with the unstable syntax mechanism.
-        let default = if self.eat(&token::Eq) {
-            // The gated span goes from the `=` to the end of the const argument that follows (and
-            // which could be a block expression).
-            let start = self.prev_token.span;
-            let const_arg = self.parse_const_arg()?;
-            let span = start.to(const_arg.value.span);
-            self.sess.gated_spans.gate(sym::const_generics_defaults, span);
-            Some(const_arg)
-        } else {
-            None
-        };
+        // Parse optional const generics default value.
+        let default = if self.eat(&token::Eq) { Some(self.parse_const_arg()?) } else { None };
 
         Ok(GenericParam {
             ident,