Rollup merge of #65974 - Centril:matcher-friendly-gating, r=petrochenkov

A scheme for more macro-matcher friendly pre-expansion gating

Pre-expansion gating will now avoid gating macro matchers that did not result in `Success(...)`. That is, the following is now OK despite `box 42` being a valid `expr` and that form being pre-expansion gated:

```rust
macro_rules! m {
    ($e:expr) => { 0 }; // This fails on the input below due to `, foo`.
    (box $e:expr, foo) => { 1 }; // Successful matcher, we should get `2`.
}

fn main() {
    assert_eq!(1, m!(box 42, foo));
}
```

Closes https://github.com/rust-lang/rust/issues/65846.

r? @petrochenkov
cc @Mark-Simulacrum

1 files changed, 6 insertions, 10 deletions

diff --git a/src/libsyntax/parse/parser/pat.rs b/src/libsyntax/parse/parser/pat.rs
index 969d5dd8374..cc8738edff7 100644
--- a/src/libsyntax/parse/parser/pat.rs
+++ b/src/libsyntax/parse/parser/pat.rs
@@ -8,9 +8,8 @@ use crate::mut_visit::{noop_visit_pat, noop_visit_mac, MutVisitor};
 use crate::parse::token::{self};
 use crate::print::pprust;
 use crate::source_map::{respan, Span, Spanned};
-use crate::symbol::kw;
 use crate::ThinVec;
-
+use syntax_pos::symbol::{kw, sym};
 use errors::{Applicability, DiagnosticBuilder};
 
 type Expected = Option<&'static str>;
@@ -52,11 +51,8 @@ impl<'a> Parser<'a> {
         // and no other gated or-pattern has been parsed thus far,
         // then we should really gate the leading `|`.
         // This complicated procedure is done purely for diagnostics UX.
-        if gated_leading_vert {
-            let mut or_pattern_spans = self.sess.gated_spans.or_patterns.borrow_mut();
-            if or_pattern_spans.is_empty() {
-                or_pattern_spans.push(leading_vert_span);
-            }
+        if gated_leading_vert && self.sess.gated_spans.is_ungated(sym::or_patterns) {
+            self.sess.gated_spans.gate(sym::or_patterns, leading_vert_span);
         }
 
         Ok(pat)
@@ -117,7 +113,7 @@ impl<'a> Parser<'a> {
 
         // Feature gate the or-pattern if instructed:
         if gate_or == GateOr::Yes {
-            self.sess.gated_spans.or_patterns.borrow_mut().push(or_pattern_span);
+            self.sess.gated_spans.gate(sym::or_patterns, or_pattern_span);
         }
 
         Ok(self.mk_pat(or_pattern_span, PatKind::Or(pats)))
@@ -325,7 +321,7 @@ impl<'a> Parser<'a> {
             } else if self.eat_keyword(kw::Box) {
                 // Parse `box pat`
                 let pat = self.parse_pat_with_range_pat(false, None)?;
-                self.sess.gated_spans.box_patterns.borrow_mut().push(lo.to(self.prev_span));
+                self.sess.gated_spans.gate(sym::box_patterns, lo.to(self.prev_span));
                 PatKind::Box(pat)
             } else if self.can_be_ident_pat() {
                 // Parse `ident @ pat`
@@ -612,7 +608,7 @@ impl<'a> Parser<'a> {
     }
 
     fn excluded_range_end(&self, span: Span) -> RangeEnd {
-        self.sess.gated_spans.exclusive_range_pattern.borrow_mut().push(span);
+        self.sess.gated_spans.gate(sym::exclusive_range_pattern, span);
         RangeEnd::Excluded
     }