rustc: Correctly pretty-print macro delimiters

This commit updates the `Mac_` AST structure to keep track of the delimiters
that it originally had for its invocation. This allows us to faithfully
pretty-print macro invocations not using parentheses (e.g. `vec![...]`). This in
turn helps procedural macros due to #43081.

Closes #50840

1 files changed, 1 insertions, 0 deletions

diff --git a/src/libsyntax/ext/placeholders.rs b/src/libsyntax/ext/placeholders.rs
index 9f60882ca29..5c1c661fffd 100644
--- a/src/libsyntax/ext/placeholders.rs
+++ b/src/libsyntax/ext/placeholders.rs
@@ -27,6 +27,7 @@ pub fn placeholder(kind: ExpansionKind, id: ast::NodeId) -> Expansion {
         dummy_spanned(ast::Mac_ {
             path: ast::Path { span: DUMMY_SP, segments: Vec::new() },
             tts: TokenStream::empty().into(),
+            delim: ast::MacDelimiter::Brace,
         })
     }