Merge #2724

2724: Improve const generic parsing r=matklad a=mchesser

Add support for generic arguments in:

`impl` type parameters:

```rust
impl<const N: u32> Bar<N> {}
```

type args:

```rust
type A = B<1, { 2 }>;
test::<10>();
```

Co-authored-by: Michael Chesser <[email protected]>

1 files changed, 3 insertions, 0 deletions

diff --git a/xtask/src/ast_src.rs b/xtask/src/ast_src.rs
index d494a4a38..67d1f41bc 100644
--- a/xtask/src/ast_src.rs
+++ b/xtask/src/ast_src.rs
@@ -206,6 +206,7 @@ pub(crate) const KINDS_SRC: KindsSrc = KindsSrc {
         "LIFETIME_ARG",
         "TYPE_ARG",
         "ASSOC_TYPE_ARG",
+        "CONST_ARG",
         "PARAM_LIST",
         "PARAM",
         "SELF_PARAM",
@@ -511,10 +512,12 @@ pub(crate) const AST_SRC: AstSrc = AstSrc {
             type_args: [TypeArg],
             lifetime_args: [LifetimeArg],
             assoc_type_args: [AssocTypeArg],
+            const_arg: [ConstArg],
         }
         struct TypeArg { TypeRef }
         struct AssocTypeArg { NameRef, TypeRef }
         struct LifetimeArg {}
+        struct ConstArg { Literal, BlockExpr }
 
         struct MacroItems: ModuleItemOwner, FnDefOwner { }