Remove MacDelimiter.

It's the same as `Delimiter`, minus the `Invisible` variant. I'm
generally in favour of using types to make impossible states
unrepresentable, but this one feels very low-value, and the conversions
between the two types are annoying and confusing.

Look at the change in `src/tools/rustfmt/src/expr.rs` for an example:
the old code converted from `MacDelimiter` to `Delimiter` and back
again, for no good reason. This suggests the author was confused about
the types.

compiler/rustc_parse/src/parser/expr.rs

@@ -2599,7 +2599,7 @@ impl<'a> Parser<'a> {
 
         // Recover from missing expression in `for` loop
         if matches!(expr.kind, ExprKind::Block(..))
-            && !matches!(self.token.kind, token::OpenDelim(token::Delimiter::Brace))
+            && !matches!(self.token.kind, token::OpenDelim(Delimiter::Brace))
             && self.may_recover()
         {
             self.sess

compiler/rustc_parse/src/parser/item.rs

@@ -9,12 +9,12 @@ use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, TokenKind};
 use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree};
 use rustc_ast::util::case::Case;
+use rustc_ast::MacCall;
 use rustc_ast::{self as ast, AttrVec, Attribute, DUMMY_NODE_ID};
 use rustc_ast::{Async, Const, Defaultness, IsAuto, Mutability, Unsafe, UseTree, UseTreeKind};
 use rustc_ast::{BindingAnnotation, Block, FnDecl, FnSig, Param, SelfKind};
 use rustc_ast::{EnumDef, FieldDef, Generics, TraitRef, Ty, TyKind, Variant, VariantData};
 use rustc_ast::{FnHeader, ForeignItem, Path, PathSegment, Visibility, VisibilityKind};
-use rustc_ast::{MacCall, MacDelimiter};
 use rustc_ast_pretty::pprust;
 use rustc_errors::{
     struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic, PResult,
@@ -1968,7 +1968,7 @@ impl<'a> Parser<'a> {
             let arrow = TokenTree::token_alone(token::FatArrow, pspan.between(bspan)); // `=>`
             let tokens = TokenStream::new(vec![params, arrow, body]);
             let dspan = DelimSpan::from_pair(pspan.shrink_to_lo(), bspan.shrink_to_hi());
-            P(DelimArgs { dspan, delim: MacDelimiter::Brace, tokens })
+            P(DelimArgs { dspan, delim: Delimiter::Brace, tokens })
         } else {
             return self.unexpected();
         };

compiler/rustc_parse/src/parser/mod.rs

@@ -25,7 +25,7 @@ use rustc_ast::util::case::Case;
 use rustc_ast::AttrId;
 use rustc_ast::DUMMY_NODE_ID;
 use rustc_ast::{self as ast, AnonConst, Const, DelimArgs, Extern};
-use rustc_ast::{Async, AttrArgs, AttrArgsEq, Expr, ExprKind, MacDelimiter, Mutability, StrLit};
+use rustc_ast::{Async, AttrArgs, AttrArgsEq, Expr, ExprKind, Mutability, StrLit};
 use rustc_ast::{HasAttrs, HasTokens, Unsafe, Visibility, VisibilityKind};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashMap;
@@ -1216,12 +1216,10 @@ impl<'a> Parser<'a> {
             || self.check(&token::OpenDelim(Delimiter::Brace));
 
         delimited.then(|| {
-            // We've confirmed above that there is a delimiter so unwrapping is OK.
             let TokenTree::Delimited(dspan, delim, tokens) = self.parse_token_tree() else {
                 unreachable!()
             };
-
-            DelimArgs { dspan, delim: MacDelimiter::from_token(delim).unwrap(), tokens }
+            DelimArgs { dspan, delim, tokens }
         })
     }
 

compiler/rustc_parse/src/parser/stmt.rs

@@ -193,10 +193,9 @@ impl<'a> Parser<'a> {
     /// At this point, the `!` token after the path has already been eaten.
     fn parse_stmt_mac(&mut self, lo: Span, attrs: AttrVec, path: ast::Path) -> PResult<'a, Stmt> {
         let args = self.parse_delim_args()?;
-        let delim = args.delim.to_token();
         let hi = self.prev_token.span;
 
-        let style = match delim {
+        let style = match args.delim {
             Delimiter::Brace => MacStmtStyle::Braces,
             _ => MacStmtStyle::NoBraces,
         };