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, 4 insertions, 1 deletions

diff --git a/crates/ra_parser/src/grammar/items/traits.rs b/crates/ra_parser/src/grammar/items/traits.rs
index 2c560e824..964fd3041 100644
--- a/crates/ra_parser/src/grammar/items/traits.rs
+++ b/crates/ra_parser/src/grammar/items/traits.rs
@@ -100,6 +100,8 @@ pub(crate) fn impl_item_list(p: &mut Parser) {
     m.complete(p, ITEM_LIST);
 }
 
+// test impl_type_params
+// impl<const N: u32> Bar<N> {}
 fn choose_type_params_over_qpath(p: &Parser) -> bool {
     // There's an ambiguity between generic parameters and qualified paths in impls.
     // If we see `<` it may start both, so we have to inspect some following tokens.
@@ -107,6 +109,7 @@ fn choose_type_params_over_qpath(p: &Parser) -> bool {
     // but not qualified paths (with one exception):
     //     `<` `>` - empty generic parameters
     //     `<` `#` - generic parameters with attributes
+    //     `<` `const` - const generic parameters
     //     `<` (LIFETIME|IDENT) `>` - single generic parameter
     //     `<` (LIFETIME|IDENT) `,` - first generic parameter in a list
     //     `<` (LIFETIME|IDENT) `:` - generic parameter with bounds
@@ -119,7 +122,7 @@ fn choose_type_params_over_qpath(p: &Parser) -> bool {
     if !p.at(T![<]) {
         return false;
     }
-    if p.nth(1) == T![#] || p.nth(1) == T![>] {
+    if p.nth(1) == T![#] || p.nth(1) == T![>] || p.nth(1) == CONST_KW {
         return true;
     }
     (p.nth(1) == LIFETIME || p.nth(1) == IDENT)