fix(formatter): print comments before fat arrow as-is for ArrowFunctionExpression

Author: Dunqing

crates/oxc_formatter/src/write/arrow_function_expression.rs

@@ -10,7 +10,10 @@ use crate::{
         Buffer, Comments, Format, FormatError, FormatResult, Formatter, SourceText,
         buffer::RemoveSoftLinesBuffer,
         prelude::*,
-        trivia::{FormatLeadingComments, format_trailing_comments},
+        trivia::{
+            DanglingIndentMode, FormatDanglingComments, FormatLeadingComments,
+            FormatTrailingComments, format_trailing_comments,
+        },
     },
     options::FormatTrailingCommas,
     utils::{assignment_like::AssignmentLikeLayout, expression::ExpressionLeftSide},
@@ -559,7 +562,12 @@ impl<'a> Format<'a> for ArrowChain<'a, '_> {
                 Ok(())
             });
 
-            write!(f, [group(&join_signatures).should_expand(*expand_signatures)])
+            FormatContentWithCacheMode::new(
+                self.head.span(),
+                group(&join_signatures).should_expand(*expand_signatures),
+                self.options.cache_mode,
+            )
+            .fmt(f)
         });
 
         let format_tail_body_inner = format_with(|f| {
@@ -758,12 +766,12 @@ fn format_signature<'a, 'b>(
             )?;
         }
 
-        // TODO: for case `a = (x: any): x is string /* comment */ => {}`
-        // if f.comments().has_dangling_comments(arrow.span()) {
-        //     write!(f, [space(), format_dangling_comments(arrow.span())])?;
-        // }
-
-        Ok(())
+        // Print comments before the fat arrow (`=>`)
+        let comments_before_fat_arrow =
+            f.context().comments().comments_before_character(arrow.params.span().end, b'=');
+        let content =
+            format_once(|f| FormatTrailingComments::Comments(comments_before_fat_arrow).fmt(f));
+        write!(f, [FormatContentWithCacheMode::new(arrow.span, content, cache_mode)])
     })
 }
 

crates/oxc_formatter/tests/fixtures/js/comments/arrow.js

@@ -4,4 +4,24 @@
 
 () =>
   // comment
-  ({})
+  ({});
+
+() /* comment1 */ => /* comment2 */ { };
+
+() /**/ => //
+  () /**/ => /**/
+    () /**/ => /**/ {
+      //
+    }
+
+call(
+  () /* comment1 */ => /* comment2 */ { }
+);
+
+call(
+  () /**/ => //
+    () /**/ => /**/
+      () /**/ => /**/ {
+        //
+      }
+);

crates/oxc_formatter/tests/fixtures/js/comments/arrow.js.snap

@@ -8,7 +8,27 @@ source: crates/oxc_formatter/tests/fixtures/mod.rs
 
 () =>
   // comment
-  ({})
+  ({});
+
+() /* comment1 */ => /* comment2 */ { };
+
+() /**/ => //
+  () /**/ => /**/
+    () /**/ => /**/ {
+      //
+    }
+
+call(
+  () /* comment1 */ => /* comment2 */ { }
+);
+
+call(
+  () /**/ => //
+    () /**/ => /**/
+      () /**/ => /**/ {
+        //
+      }
+);
 
 ==================== Output ====================
 () =>
@@ -19,4 +39,24 @@ source: crates/oxc_formatter/tests/fixtures/mod.rs
   // comment
   ({});
 
+() /* comment1 */ => /* comment2 */ {};
+
+() /**/ =>
+  //
+  () /**/ =>
+  /**/
+  () /**/ => /**/ {
+    //
+  };
+
+call(() /* comment1 */ => /* comment2 */ {});
+
+call(() /**/ =>
+  //
+  () /**/ =>
+  /**/
+  () /**/ => /**/ {
+  //
+});
+
 ===================== End =====================