fix(formatter): ignore comment does not work for sequence expressions in arrow function body

Author: Dunqing

crates/oxc_formatter/src/print/arrow_function_expression.rs

@@ -1,5 +1,5 @@
 use oxc_ast::ast::*;
-use oxc_span::GetSpan;
+use oxc_span::{GetSpan, Span};
 
 use crate::{
     ast_nodes::{AstNode, AstNodes},
@@ -13,6 +13,7 @@ use crate::{
     utils::{
         assignment_like::AssignmentLikeLayout, expression::ExpressionLeftSide,
         format_node_without_trailing_comments::FormatNodeWithoutTrailingComments,
+        suppressed::FormatSuppressedNode,
     },
     write,
 };
@@ -143,20 +144,10 @@ impl<'a, 'b> FormatJsArrowFunctionExpression<'a, 'b> {
                 let arrow_expression = arrow.get_expression();
 
                 if let Some(Expression::SequenceExpression(sequence)) = arrow_expression {
-                    return if f.context().comments().has_comment_before(sequence.span().start) {
-                        write!(
-                            f,
-                            [group(&format_args!(
-                                formatted_signature,
-                                group(&format_args!(indent(&format_args!(
-                                    hard_line_break(),
-                                    format_leading_comments(sequence.span()),
-                                    token("("),
-                                    format_body,
-                                    token(")")
-                                ))))
-                            ))]
-                        );
+                    return if let Some(format_sequence) =
+                        format_sequence_with_leading_comment(sequence.span(), &format_body, f)
+                    {
+                        write!(f, [group(&format_args!(formatted_signature, format_sequence))]);
                     } else {
                         write!(
                             f,
@@ -564,17 +555,10 @@ impl<'a> Format<'a> for ArrowChain<'a, '_> {
             // Ensure that the parens of sequence expressions end up on their own line if the
             // body breaks
             if let Some(Expression::SequenceExpression(sequence)) = tail.get_expression() {
-                if f.context().comments().has_comment_before(sequence.span().start) {
-                    write!(
-                        f,
-                        [group(&format_args!(indent(&format_args!(
-                            hard_line_break(),
-                            format_leading_comments(sequence.span()),
-                            token("("),
-                            format_tail_body,
-                            token(")")
-                        ))))]
-                    );
+                if let Some(format_sequence) =
+                    format_sequence_with_leading_comment(sequence.span(), &format_tail_body, f)
+                {
+                    write!(f, format_sequence);
                 } else {
                     write!(
                         f,
@@ -761,3 +745,44 @@ impl<'a> Format<'a> for FormatMaybeCachedFunctionBody<'a, '_> {
         FormatContentWithCacheMode::new(self.body.span, content, self.mode).fmt(f);
     }
 }
+
+/// Format a sequence expression in an arrow function body that has a leading comment.
+///
+/// When an arrow function body is a sequence expression (e.g., `() => (a, b, c)`) and has
+/// a leading comment, special formatting is needed to place the comment correctly:
+///
+/// ```js
+/// const f = () =>
+///   // comment
+///   (a, b, c);
+/// ```
+///
+/// Returns `Some(formatter)` if the sequence has a leading comment, `None` otherwise.
+/// When `None`, the caller should use normal formatting with `soft_block_indent`.
+///
+/// Handles `oxfmt-ignore` by preserving original source text when suppressed.
+fn format_sequence_with_leading_comment<'a, 'b>(
+    sequence_span: Span,
+    format_body: &'b impl Format<'a>,
+    f: &Formatter<'_, 'a>,
+) -> Option<impl Format<'a> + 'b> {
+    if !f.comments().has_comment_before(sequence_span.start) {
+        return None;
+    }
+
+    let is_suppressed = f.comments().is_suppressed(sequence_span.start);
+
+    let format_sequence = format_with(move |f| {
+        write!(f, [format_leading_comments(sequence_span), "("]);
+        if is_suppressed {
+            write!(f, FormatSuppressedNode(sequence_span));
+        } else {
+            write!(f, format_body);
+        }
+        write!(f, [")"]);
+    });
+
+    Some(format_with(move |f| {
+        write!(f, group(&indent(&format_args!(hard_line_break(), format_sequence))));
+    }))
+}

tasks/prettier_conformance/snapshots/prettier.js.snap.md

@@ -1,4 +1,4 @@
-js compatibility: 743/753 (98.67%)
+js compatibility: 744/753 (98.80%)
 
 # Failed
 
@@ -13,4 +13,3 @@ js compatibility: 743/753 (98.67%)
 | js/last-argument-expansion/dangling-comment-in-arrow-function.js | 💥 | 22.22% |
 | js/quote-props/objects.js | 💥💥✨✨ | 48.04% |
 | js/quote-props/with_numbers.js | 💥💥✨✨ | 46.43% |
-| js/sequence-expression/ignored.js | 💥 | 66.67% |