From 078a6f68e170033250888604caca3b5ea5a3d4b7 Mon Sep 17 00:00:00 2001
From: Ed Page <eopage@gmail.com>
Date: Thu, 20 Feb 2025 09:57:54 -0600
Subject: [PATCH] feat(pretty): Preserve the frontmatter

---
 compiler/rustc_ast_pretty/src/pprust/state.rs | 9 +++++++++
 tests/ui/unpretty/frontmatter.stdout          | 2 ++
 2 files changed, 11 insertions(+)

diff --git a/compiler/rustc_ast_pretty/src/pprust/state.rs b/compiler/rustc_ast_pretty/src/pprust/state.rs
index 01fc272a45897..03572a86735c1 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state.rs
@@ -121,6 +121,15 @@ fn gather_comments(sm: &SourceMap, path: FileName, src: String) -> Vec<Comment>
         pos += shebang_len;
     }
 
+    if let Some(frontmatter_len) = rustc_lexer::strip_frontmatter(&text[pos..]) {
+        comments.push(Comment {
+            style: CommentStyle::Isolated,
+            lines: vec![text[pos..pos + frontmatter_len].to_string()],
+            pos: start_bpos + BytePos(pos as u32),
+        });
+        pos += frontmatter_len;
+    }
+
     for token in rustc_lexer::tokenize(&text[pos..]) {
         let token_text = &text[pos..pos + token.len as usize];
         match token.kind {
diff --git a/tests/ui/unpretty/frontmatter.stdout b/tests/ui/unpretty/frontmatter.stdout
index 9ad6bbbe5774b..2ccbb1b258255 100644
--- a/tests/ui/unpretty/frontmatter.stdout
+++ b/tests/ui/unpretty/frontmatter.stdout
@@ -1,3 +1,5 @@
+---
+---
 
 //@ compile-flags: -Zunpretty=normal
 //@ check-pass