fix(formatter): incorrect printing of dangling comments in the if statement

crates/oxc_formatter/src/utils/statement_body.rs

@@ -37,9 +37,13 @@ impl<'a> Format<'a> for FormatStatementBody<'a, '_> {
             write!(f, empty);
         } else if let AstNodes::BlockStatement(block) = self.body.as_ast_nodes() {
             write!(f, [space()]);
-            // Use `write` instead of `format` to avoid printing leading comments of the block.
-            // Those comments should be printed inside the block statement.
-            block.write(f);
+            if matches!(self.body.parent, AstNodes::IfStatement(_)) {
+                write!(f, [block]);
+            } else {
+                // Use `write` instead of `format` to avoid printing leading comments of the block.
+                // Those comments should be printed inside the block statement.
+                block.write(f);
+            }
         } else if self.force_space {
             write!(f, [space(), self.body]);
         } else {

crates/oxc_formatter/src/write/mod.rs

@@ -768,10 +768,7 @@ impl<'a> FormatWrite<'a> for AstNode<'a, IfStatement<'a>> {
                 "if",
                 space(),
                 "(",
-                group(&soft_block_indent(&format_args!(
-                    FormatTestOfIfAndWhileStatement(test),
-                    FormatCommentForEmptyStatement(consequent)
-                ))),
+                group(&soft_block_indent(&FormatTestOfIfAndWhileStatement(test))),
                 ")",
                 FormatStatementBody::new(consequent),
             ))
@@ -780,38 +777,36 @@ impl<'a> FormatWrite<'a> for AstNode<'a, IfStatement<'a>> {
             let alternate_start = alternate.span().start;
             let comments = f.context().comments().comments_before(alternate_start);
 
-            let has_line_comment = comments.iter().any(|comment| comment.kind == CommentKind::Line);
-            let has_dangling_comments = has_line_comment
-                || comments.last().is_some_and(|last_comment| {
+            let has_line_comment = comments.iter().any(|comment| comment.is_line());
+            let has_dangling_comments = comments
+                .last()
+                .or(f.comments().printed_comments().last())
+                .is_some_and(|last_comment| {
                     // Ensure the comments are placed before the else keyword or on a new line
-                    f.source_text()
-                        .slice_range(last_comment.span.end, alternate_start)
-                        .contains("else")
-                        || f.source_text()
-                            .contains_newline_between(last_comment.span.end, alternate_start)
+                    f.source_text().slice_range(last_comment.span.end, alternate_start).trim()
+                        == "else"
                 });
 
-            let else_on_same_line =
-                matches!(consequent.as_ref(), Statement::BlockStatement(_)) && !has_line_comment;
+            let else_on_same_line = matches!(consequent.as_ref(), Statement::BlockStatement(_))
+                && (!has_line_comment || !has_dangling_comments);
 
             if else_on_same_line {
-                write!(f, space());
+                write!(f, [space(), has_dangling_comments.then(line_suffix_boundary)]);
             } else {
                 write!(f, hard_line_break());
             }
 
-            if has_dangling_comments {
+            if has_dangling_comments && let Some(first_comment) = comments.first() {
+                if f.source_text().get_lines_before(first_comment.span, f.comments()) > 1 {
+                    write!(f, empty_line());
+                }
+                write!(
+                    f,
+                    FormatDanglingComments::Comments { comments, indent: DanglingIndentMode::None }
+                );
                 if has_line_comment {
-                    write!(f, FormatTrailingComments::Comments(comments));
                     write!(f, hard_line_break());
                 } else {
-                    write!(
-                        f,
-                        FormatDanglingComments::Comments {
-                            comments,
-                            indent: DanglingIndentMode::None
-                        }
-                    );
                     write!(f, space());
                 }
             }
@@ -820,6 +815,7 @@ impl<'a> FormatWrite<'a> for AstNode<'a, IfStatement<'a>> {
                 f,
                 [
                     "else",
+                    line_suffix_boundary(),
                     group(&FormatStatementBody::new(alternate).with_forced_space(matches!(
                         alternate.as_ref(),
                         Statement::IfStatement(_)

crates/oxc_formatter/tests/fixtures/js/if/issue-16137.js

@@ -0,0 +1,10 @@
+if (x) {
+  // test
+} //test
+else if (x) {
+  // test
+}
+
+if (cond) stuff;
+/* comment*/
+else stuff;

crates/oxc_formatter/tests/fixtures/js/if/issue-16137.js.snap

@@ -0,0 +1,43 @@
+---
+source: crates/oxc_formatter/tests/fixtures/mod.rs
+---
+==================== Input ====================
+if (x) {
+  // test
+} //test
+else if (x) {
+  // test
+}
+
+if (cond) stuff;
+/* comment*/
+else stuff;
+
+==================== Output ====================
+------------------
+{ printWidth: 80 }
+------------------
+if (x) {
+  // test
+} //test
+else if (x) {
+  // test
+}
+
+if (cond) stuff;
+/* comment*/ else stuff;
+
+-------------------
+{ printWidth: 100 }
+-------------------
+if (x) {
+  // test
+} //test
+else if (x) {
+  // test
+}
+
+if (cond) stuff;
+/* comment*/ else stuff;
+
+===================== End =====================

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

@@ -1,4 +1,4 @@
-js compatibility: 729/759 (96.05%)
+js compatibility: 734/759 (96.71%)
 
 # Failed
 
@@ -9,7 +9,6 @@ js compatibility: 729/759 (96.05%)
 | js/comments/dangling_for.js | 💥💥 | 22.22% |
 | js/comments/empty-statements.js | 💥💥 | 90.91% |
 | js/comments/function-declaration.js | 💥💥 | 92.80% |
-| js/comments/if.js | 💥💥 | 74.83% |
 | js/comments/return-statement.js | 💥💥 | 98.28% |
 | js/explicit-resource-management/for-await-using-of-comments.js | 💥 | 0.00% |
 | js/explicit-resource-management/valid-await-using-comments.js | 💥 | 68.57% |
@@ -19,10 +18,6 @@ js compatibility: 729/759 (96.05%)
 | js/for/parentheses.js | 💥 | 97.96% |
 | js/identifier/for-of/let.js | 💥 | 92.31% |
 | js/identifier/parentheses/let.js | 💥💥 | 82.27% |
-| js/if/comment-between-condition-and-body.js | 💥 | 65.79% |
-| js/if/expr_and_same_line_comments.js | 💥 | 97.73% |
-| js/if/if_comments.js | 💥 | 76.00% |
-| js/if/trailing_comment.js | 💥 | 91.43% |
 | js/last-argument-expansion/dangling-comment-in-arrow-function.js | 💥 | 22.22% |
 | js/object-multiline/multiline.js | 💥✨ | 22.22% |
 | js/quotes/objects.js | 💥💥 | 80.00% |