Add newtype for trailing in parser

5 files changed, 30 insertions, 21 deletions

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 081f30ef11a..cb46eb25fa4 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -4,7 +4,7 @@ use super::pat::{CommaRecoveryMode, Expected, RecoverColon, RecoverComma};
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{
     AttrWrapper, BlockMode, ClosureSpans, ForceCollect, Parser, PathStyle, Recovered, Restrictions,
-    SemiColonMode, SeqSep, TokenExpectType, TokenType, TrailingToken,
+    SemiColonMode, SeqSep, TokenExpectType, TokenType, Trailing, TrailingToken,
 };
 
 use crate::errors;
@@ -1561,7 +1561,7 @@ impl<'a> Parser<'a> {
                 return Ok(self.recover_seq_parse_error(Delimiter::Parenthesis, lo, err));
             }
         };
-        let kind = if es.len() == 1 && !trailing_comma {
+        let kind = if es.len() == 1 && matches!(trailing_comma, Trailing::No) {
             // `(e)` is parenthesized `e`.
             ExprKind::Paren(es.into_iter().next().unwrap())
         } else {
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 6e9af1e15d8..b9fbf1c5765 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -1,7 +1,8 @@
 use super::diagnostics::{dummy_arg, ConsumeClosingDelim};
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{
-    AttrWrapper, FollowedByType, ForceCollect, Parser, PathStyle, Recovered, TrailingToken,
+    AttrWrapper, FollowedByType, ForceCollect, Parser, PathStyle, Recovered, Trailing,
+    TrailingToken,
 };
 use crate::errors::{self, MacroExpandsToAdtField};
 use crate::fluent_generated as fluent;
@@ -1459,7 +1460,7 @@ impl<'a> Parser<'a> {
         let (variants, _) = if self.token == TokenKind::Semi {
             self.dcx().emit_err(errors::UseEmptyBlockNotSemi { span: self.token.span });
             self.bump();
-            (thin_vec![], false)
+            (thin_vec![], Trailing::No)
         } else {
             self.parse_delim_comma_seq(Delimiter::Brace, |p| p.parse_enum_variant(id.span))
                 .map_err(|mut err| {
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 27e9fb10a9f..29dd2eeb56a 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -371,6 +371,12 @@ impl From<Recovered> for bool {
     }
 }
 
+#[derive(Copy, Clone, Debug)]
+pub enum Trailing {
+    No,
+    Yes,
+}
+
 #[derive(Clone, Copy, PartialEq, Eq)]
 pub enum TokenDescription {
     ReservedIdentifier,
@@ -797,10 +803,10 @@ impl<'a> Parser<'a> {
         sep: SeqSep,
         expect: TokenExpectType,
         mut f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
-    ) -> PResult<'a, (ThinVec<T>, bool /* trailing */, Recovered)> {
+    ) -> PResult<'a, (ThinVec<T>, Trailing, Recovered)> {
         let mut first = true;
         let mut recovered = Recovered::No;
-        let mut trailing = false;
+        let mut trailing = Trailing::No;
         let mut v = ThinVec::new();
 
         while !self.expect_any_with_type(kets, expect) {
@@ -914,7 +920,7 @@ impl<'a> Parser<'a> {
                 }
             }
             if sep.trailing_sep_allowed && self.expect_any_with_type(kets, expect) {
-                trailing = true;
+                trailing = Trailing::Yes;
                 break;
             }
 
@@ -992,7 +998,7 @@ impl<'a> Parser<'a> {
         ket: &TokenKind,
         sep: SeqSep,
         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
-    ) -> PResult<'a, (ThinVec<T>, bool /* trailing */, Recovered)> {
+    ) -> PResult<'a, (ThinVec<T>, Trailing, Recovered)> {
         self.parse_seq_to_before_tokens(&[ket], sep, TokenExpectType::Expect, f)
     }
 
@@ -1004,7 +1010,7 @@ impl<'a> Parser<'a> {
         ket: &TokenKind,
         sep: SeqSep,
         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
-    ) -> PResult<'a, (ThinVec<T>, bool /* trailing */)> {
+    ) -> PResult<'a, (ThinVec<T>, Trailing)> {
         let (val, trailing, recovered) = self.parse_seq_to_before_end(ket, sep, f)?;
         if matches!(recovered, Recovered::No) {
             self.eat(ket);
@@ -1021,7 +1027,7 @@ impl<'a> Parser<'a> {
         ket: &TokenKind,
         sep: SeqSep,
         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
-    ) -> PResult<'a, (ThinVec<T>, bool /* trailing */)> {
+    ) -> PResult<'a, (ThinVec<T>, Trailing)> {
         self.expect(bra)?;
         self.parse_seq_to_end(ket, sep, f)
     }
@@ -1033,7 +1039,7 @@ impl<'a> Parser<'a> {
         &mut self,
         delim: Delimiter,
         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
-    ) -> PResult<'a, (ThinVec<T>, bool /* trailing */)> {
+    ) -> PResult<'a, (ThinVec<T>, Trailing)> {
         self.parse_unspanned_seq(
             &token::OpenDelim(delim),
             &token::CloseDelim(delim),
@@ -1048,7 +1054,7 @@ impl<'a> Parser<'a> {
     fn parse_paren_comma_seq<T>(
         &mut self,
         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
-    ) -> PResult<'a, (ThinVec<T>, bool /* trailing */)> {
+    ) -> PResult<'a, (ThinVec<T>, Trailing)> {
         self.parse_delim_comma_seq(Delimiter::Parenthesis, f)
     }
 
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 072db24265e..2ede19b11e0 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -1,4 +1,4 @@
-use super::{ForceCollect, Parser, PathStyle, Restrictions, TrailingToken};
+use super::{ForceCollect, Parser, PathStyle, Restrictions, Trailing, TrailingToken};
 use crate::errors::{
     self, AmbiguousRangePattern, DotDotDotForRemainingFields, DotDotDotRangeToPatternNotAllowed,
     DotDotDotRestPattern, EnumPatternInsteadOfIdentifier, ExpectedBindingLeftOfAt,
@@ -696,7 +696,9 @@ impl<'a> Parser<'a> {
 
         // Here, `(pat,)` is a tuple pattern.
         // For backward compatibility, `(..)` is a tuple pattern as well.
-        Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
+        let paren_pattern =
+            fields.len() == 1 && !(matches!(trailing_comma, Trailing::Yes) || fields[0].is_rest());
+        if paren_pattern {
             let pat = fields.into_iter().next().unwrap();
             let close_paren = self.prev_token.span;
 
@@ -714,7 +716,7 @@ impl<'a> Parser<'a> {
                         },
                     });
 
-                    self.parse_pat_range_begin_with(begin.clone(), form)?
+                    self.parse_pat_range_begin_with(begin.clone(), form)
                 }
                 // recover ranges with parentheses around the `(start)..`
                 PatKind::Err(_)
@@ -729,15 +731,15 @@ impl<'a> Parser<'a> {
                         },
                     });
 
-                    self.parse_pat_range_begin_with(self.mk_expr(pat.span, ExprKind::Err), form)?
+                    self.parse_pat_range_begin_with(self.mk_expr(pat.span, ExprKind::Err), form)
                 }
 
                 // (pat) with optional parentheses
-                _ => PatKind::Paren(pat),
+                _ => Ok(PatKind::Paren(pat)),
             }
         } else {
-            PatKind::Tuple(fields)
-        })
+            Ok(PatKind::Tuple(fields))
+        }
     }
 
     /// Parse a mutable binding with the `mut` token already eaten.
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index f79f2a813b2..d65e06494fc 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -1,4 +1,4 @@
-use super::{Parser, PathStyle, TokenType};
+use super::{Parser, PathStyle, TokenType, Trailing};
 
 use crate::errors::{
     self, DynAfterMut, ExpectedFnPathFoundFnKeyword, ExpectedMutOrConstInRawPointerType,
@@ -415,7 +415,7 @@ impl<'a> Parser<'a> {
             Ok(ty)
         })?;
 
-        if ts.len() == 1 && !trailing {
+        if ts.len() == 1 && matches!(trailing, Trailing::No) {
             let ty = ts.into_iter().next().unwrap().into_inner();
             let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
             match ty.kind {