Auto merge of #79278 - mark-i-m:stabilize-or-pattern, r=nikomatsakis

Stabilize or_patterns (RFC 2535, 2530, 2175)

closes #54883

This PR stabilizes the or_patterns feature in Rust 1.53.

This is blocked on the following (in order):
- [x] The crater run in https://github.com/rust-lang/rust/pull/78935#issuecomment-731564021
- [x] The resolution of the unresolved questions and a second crater run (https://github.com/rust-lang/rust/pull/78935#issuecomment-735412705)
    - It looks like we will need to pursue some sort of edition-based transition for `:pat`.
- [x] Nomination and discussion by T-lang
- [x] Implement new behavior for `:pat` based on consensus (https://github.com/rust-lang/rust/pull/80100).
- [ ] An FCP on stabilization

EDIT: Stabilization report is in https://github.com/rust-lang/rust/pull/79278#issuecomment-772815177

compiler/rustc_expand/src/expand.rs

@@ -22,7 +22,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{Applicability, PResult};
 use rustc_feature::Features;
-use rustc_parse::parser::{AttemptLocalParseRecovery, ForceCollect, GateOr, Parser, RecoverComma};
+use rustc_parse::parser::{AttemptLocalParseRecovery, ForceCollect, Parser, RecoverComma};
 use rustc_parse::validate_attr;
 use rustc_session::lint::builtin::UNUSED_DOC_COMMENTS;
 use rustc_session::lint::BuiltinLintDiagnostics;
@@ -917,7 +917,7 @@ pub fn parse_ast_fragment<'a>(
         }
         AstFragmentKind::Ty => AstFragment::Ty(this.parse_ty()?),
         AstFragmentKind::Pat => {
-            AstFragment::Pat(this.parse_pat_allow_top_alt(None, GateOr::Yes, RecoverComma::No)?)
+            AstFragment::Pat(this.parse_pat_allow_top_alt(None, RecoverComma::No)?)
         }
         AstFragmentKind::Arms
         | AstFragmentKind::Fields

compiler/rustc_expand/src/lib.rs

@@ -2,7 +2,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(decl_macro)]
 #![feature(destructuring_assignment)]
-#![feature(or_patterns)]
+#![cfg_attr(bootstrap, feature(or_patterns))]
 #![feature(proc_macro_diagnostic)]
 #![feature(proc_macro_internals)]
 #![feature(proc_macro_span)]