Rollup merge of #82579 - osa1:issue82566, r=estebank

Fix turbofish recovery with multiple generic args

This consists of two commits, each can be individually reviewed.

- First commit fixes the issue in [this comment](https://github.com/rust-lang/rust/issues/82566#issuecomment-786924466).
- Second commit fixes #82566

---

r? ````@estebank````

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -662,7 +662,7 @@ impl<'a> Parser<'a> {
                     let x = self.parse_seq_to_before_end(
                         &token::Gt,
                         SeqSep::trailing_allowed(token::Comma),
-                        |p| p.parse_ty(),
+                        |p| p.parse_generic_arg(),
                     );
                     match x {
                         Ok((_, _, false)) => {

compiler/rustc_parse/src/parser/path.rs

@@ -545,7 +545,7 @@ impl<'a> Parser<'a> {
 
     /// Parse a generic argument in a path segment.
     /// This does not include constraints, e.g., `Item = u8`, which is handled in `parse_angle_arg`.
-    fn parse_generic_arg(&mut self) -> PResult<'a, Option<GenericArg>> {
+    pub(super) fn parse_generic_arg(&mut self) -> PResult<'a, Option<GenericArg>> {
         let start = self.token.span;
         let arg = if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) {
             // Parse lifetime argument.

compiler/rustc_parse/src/parser/ty.rs

@@ -360,12 +360,20 @@ impl<'a> Parser<'a> {
             }
             Err(err) => return Err(err),
         };
+
         let ty = if self.eat(&token::Semi) {
-            TyKind::Array(elt_ty, self.parse_anon_const_expr()?)
+            let mut length = self.parse_anon_const_expr()?;
+            if let Err(e) = self.expect(&token::CloseDelim(token::Bracket)) {
+                // Try to recover from `X<Y, ...>` when `X::<Y, ...>` works
+                self.check_mistyped_turbofish_with_multiple_type_params(e, &mut length.value)?;
+                self.expect(&token::CloseDelim(token::Bracket))?;
+            }
+            TyKind::Array(elt_ty, length)
         } else {
+            self.expect(&token::CloseDelim(token::Bracket))?;
             TyKind::Slice(elt_ty)
         };
-        self.expect(&token::CloseDelim(token::Bracket))?;
+
         Ok(ty)
     }