fix(codegen): preserve newlines between comments (#6014)

fixes #6010

crates/oxc_codegen/src/comment.rs

@@ -1,7 +1,7 @@
-use oxc_syntax::identifier::is_line_terminator;
 use rustc_hash::FxHashMap;
 
 use oxc_ast::{Comment, CommentKind, Trivias};
+use oxc_syntax::identifier::is_line_terminator;
 
 use crate::Codegen;
 
@@ -34,24 +34,28 @@ impl<'a> Codegen<'a> {
         let Some(source_text) = self.source_text else { return };
         let Some(comments) = self.leading_comments.remove(&start) else { return };
 
-        let first = comments.first().unwrap();
-        if first.preceded_by_newline {
+        if comments.first().is_some_and(|c| c.preceded_by_newline) {
             // Skip printing newline if this comment is already on a newline.
             if self.peek_nth(0).is_some_and(|c| c != '\n' && c != '\t') {
-                self.print_char(b'\n');
+                self.print_hard_newline();
                 self.print_indent();
             }
         }
 
-        for comment in &comments {
-            let s = comment.real_span().source_text(source_text);
+        for (i, comment) in comments.iter().enumerate() {
+            if i >= 1 && comment.preceded_by_newline {
+                self.print_hard_newline();
+                self.print_indent();
+            }
+
+            let comment_source = comment.real_span().source_text(source_text);
             match comment.kind {
                 CommentKind::Line => {
-                    self.print_str(s);
+                    self.print_str(comment_source);
                 }
                 CommentKind::Block => {
                     // Print block comments with our own indentation.
-                    let lines = s.split(is_line_terminator);
+                    let lines = comment_source.split(is_line_terminator);
                     for line in lines {
                         if !line.starts_with("/*") {
                             self.print_indent();
@@ -65,8 +69,7 @@ impl<'a> Codegen<'a> {
             }
         }
 
-        let last = comments.last().unwrap();
-        if last.is_line() || last.followed_by_newline {
+        if comments.last().is_some_and(|c| c.is_line() || c.followed_by_newline) {
             self.print_hard_newline();
             self.print_indent();
         }

crates/oxc_codegen/tests/integration/jsdoc.rs

@@ -4,10 +4,20 @@ use crate::snapshot;
 fn comment() {
     let cases = vec![
         r"
+/**
+ * Top level
+ *
+ * @module
+ */
+
 /** This is a description of the foo function. */
 function foo() {
 }
 
+/**
+ * Preserve newline
+ */
+
 /**
  * Represents a book.
  * @constructor
@@ -19,6 +29,10 @@ function Book(title, author) {
 
 /** Class representing a point. */
 class Point {
+    /**
+     * Preserve newline
+     */
+
     /**
      * Create a point.
      * @param {number} x - The x value.

crates/oxc_codegen/tests/integration/snapshots/jsodc.snap

@@ -3,10 +3,20 @@ source: crates/oxc_codegen/tests/integration/main.rs
 ---
 ########## 0
 
+/**
+ * Top level
+ *
+ * @module
+ */
+
 /** This is a description of the foo function. */
 function foo() {
 }
 
+/**
+ * Preserve newline
+ */
+
 /**
  * Represents a book.
  * @constructor
@@ -18,6 +28,10 @@ function Book(title, author) {
 
 /** Class representing a point. */
 class Point {
+    /**
+     * Preserve newline
+     */
+
     /**
      * Create a point.
      * @param {number} x - The x value.
@@ -93,9 +107,17 @@ export enum DefinitionKind {
 }
 
 ----------
+/**
+* Top level
+*
+* @module
+*/
 /** This is a description of the foo function. */
 function foo() {}
 /**
+* Preserve newline
+*/
+/**
 * Represents a book.
 * @constructor
 * @param {string} title - The title of the book.
@@ -104,6 +126,9 @@ function foo() {}
 function Book(title, author) {}
 /** Class representing a point. */
 class Point {
+	/**
+	* Preserve newline
+	*/
 	/**
 	* Create a point.
 	* @param {number} x - The x value.
@@ -132,7 +157,8 @@ const Point = class {};
 /**
 * Shirt module.
 * @module my/shirt
-*//** Button the shirt. */
+*/
+/** Button the shirt. */
 exports.button = function() {};
 /** Unbutton the shirt. */
 exports.unbutton = function() {};

crates/oxc_isolated_declarations/examples/isolated_declarations.rs

@@ -10,7 +10,7 @@ use oxc_span::SourceType;
 // Instruction:
 // create a `test.js`,
 // run `cargo run -p oxc_isolated_declarations --example isolated_declarations`
-// or `just watch "run -p oxc_isolated_declarations --example isolated_declarations"`
+// or `just example isolated_declarations`
 
 fn main() {
     let name = env::args().nth(1).unwrap_or_else(|| "test.tsx".to_string());