refactor(formatter): align printing trailing comments with Prettier

Author: Dunqing

crates/oxc_formatter/src/formatter/format_element/document.rs

@@ -605,7 +605,9 @@ impl FormatElements for [FormatElement<'_>] {
                         return true;
                     }
                 }
-
+                FormatElement::Line(line) if line.will_break() => {
+                    return true;
+                }
                 element if ignore_depth == 0 && element.will_break() => {
                     return true;
                 }

crates/oxc_formatter/src/formatter/format_element/mod.rs

@@ -103,6 +103,10 @@ impl LineMode {
     pub const fn is_hard(self) -> bool {
         matches!(self, LineMode::Hard)
     }
+
+    pub const fn will_break(self) -> bool {
+        matches!(self, LineMode::Hard | LineMode::Empty)
+    }
 }
 
 #[derive(Debug, Clone, Copy, Eq, PartialEq)]
@@ -240,7 +244,7 @@ impl FormatElements for FormatElement<'_> {
         match self {
             FormatElement::ExpandParent => true,
             FormatElement::Tag(Tag::StartGroup(group)) => !group.mode().is_flat(),
-            FormatElement::Line(line_mode) => matches!(line_mode, LineMode::Hard | LineMode::Empty),
+            FormatElement::Line(line_mode) => line_mode.will_break(),
             FormatElement::StaticText { text } | FormatElement::DynamicText { text } => {
                 text.contains('\n')
             }

crates/oxc_formatter/src/formatter/trivia.rs

@@ -207,36 +207,35 @@ impl<'a> Format<'a> for FormatTrailingComments<'a> {
                 // trailing comment for `2`. We can simulate the above by checking
                 // if this a comment on its own line; normal trailing comments are
                 // always at the end of another expression.
-                if total_lines_before > 0 {
+                if total_lines_before > 0
+                    || previous_comment.is_some_and(|comment| comment.is_line())
+                {
                     write!(
                         f,
-                        [
-                            line_suffix(&format_with(|f| {
-                                match lines_before {
-                                    _ if should_nestle => {}
-                                    0 => {
-                                        // If the comment is immediately following a block-like comment,
-                                        // then it can stay on the same line with just a space between.
-                                        // Otherwise, it gets a hard break.
-                                        //
-                                        //   [>* hello <] // hi
-                                        //   [>*
-                                        //    * docs
-                                        //   */ [> still on the same line <]
-                                        if previous_comment.copied().is_some_and(Comment::is_line) {
-                                            write!(f, [hard_line_break()])?;
-                                        } else {
-                                            write!(f, [space()])?;
-                                        }
+                        [line_suffix(&format_with(|f| {
+                            match lines_before {
+                                _ if should_nestle => {}
+                                0 => {
+                                    // If the comment is immediately following a block-like comment,
+                                    // then it can stay on the same line with just a space between.
+                                    // Otherwise, it gets a hard break.
+                                    //
+                                    //   [>* hello <] // hi
+                                    //   [>*
+                                    //    * docs
+                                    //   */ [> still on the same line <]
+                                    if previous_comment.copied().is_some_and(Comment::is_line) {
+                                        write!(f, [hard_line_break()])?;
+                                    } else {
+                                        write!(f, [space()])?;
                                     }
-                                    1 => write!(f, [hard_line_break()])?,
-                                    _ => write!(f, [empty_line()])?,
                                 }
+                                1 => write!(f, [hard_line_break()])?,
+                                _ => write!(f, [empty_line()])?,
+                            }
 
-                                write!(f, [comment])
-                            })),
-                            expand_parent()
-                        ]
+                            write!(f, [comment])
+                        }))]
                     )?;
                 } else {
                     let content =

crates/oxc_formatter/tests/fixtures/js/comments/for-statements.js.snap

@@ -16,15 +16,13 @@ for (let i of [
 ==================== Output ====================
 for (let i in [
   // comment1
-  1, 2,
-  3,
+  1, 2, 3,
   // comment2
 ]);
 
 for (let i of [
   // comment1
-  1, 2,
-  3,
+  1, 2, 3,
   // comment2
 ]);