Rollup merge of #62550 - Centril:rest-patterns, r=petrochenkov

Implement RFC 2707 + Parser recovery for range patterns

Implement https://github.com/rust-lang/rfcs/pull/2707.

- Add a new basic syntactic pattern form `ast::PatKind::Rest` (parsed as `..` or `DOTDOT`) and simplify `ast::PatKind::{Slice, Tuple, TupleStruct}` as a result.

- Lower `ast::PatKind::Rest` in combination with the aforementioned `PatKind` variants as well as `PatKind::Ident`. The HIR remains unchanged for now (may be advisable to make slight adjustments later).

- Refactor `parser.rs` wrt. parsing sequences and lists of things in the process.

- Add parser recovery for range patterns of form `X..`, `X..=`, `X...`, `..Y`, `..=Y`, and `...Y`.
   This should make it easy to actually support these patterns semantically later if we so desire.

cc https://github.com/rust-lang/rust/issues/62254

r? @petrochenkov

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index baf1031de1e..528b27d6153 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -840,14 +840,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
     }
     fn pat_tuple_struct(&self, span: Span, path: ast::Path,
                         subpats: Vec<P<ast::Pat>>) -> P<ast::Pat> {
-        self.pat(span, PatKind::TupleStruct(path, subpats, None))
+        self.pat(span, PatKind::TupleStruct(path, subpats))
     }
     fn pat_struct(&self, span: Span, path: ast::Path,
                   field_pats: Vec<Spanned<ast::FieldPat>>) -> P<ast::Pat> {
         self.pat(span, PatKind::Struct(path, field_pats, false))
     }
     fn pat_tuple(&self, span: Span, pats: Vec<P<ast::Pat>>) -> P<ast::Pat> {
-        self.pat(span, PatKind::Tuple(pats, None))
+        self.pat(span, PatKind::Tuple(pats))
     }
 
     fn pat_some(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat> {