fix(codegen): print comments when block is empty (#7236)

part of #7190

crates/oxc_codegen/src/comment.rs

@@ -70,14 +70,15 @@ impl<'a> Codegen<'a> {
         self.print_comments(start, &comments, unused_comments);
     }
 
-    /// A statement comment also includes legal comments
-    pub(crate) fn print_statement_comments(&mut self, start: u32) {
+    pub(crate) fn get_statement_comments(
+        &mut self,
+        start: u32,
+    ) -> Option<(Vec<Comment>, Vec<Comment>)> {
         if self.options.minify {
-            return;
+            return None;
         }
-        let Some(comments) = self.comments.remove(&start) else {
-            return;
-        };
+
+        let comments = self.comments.remove(&start)?;
 
         let mut leading_comments = vec![];
         let mut unused_comments = vec![];
@@ -107,7 +108,14 @@ impl<'a> Codegen<'a> {
             unused_comments.push(comment);
         }
 
-        self.print_comments(start, &leading_comments, unused_comments);
+        Some((leading_comments, unused_comments))
+    }
+
+    /// A statement comment also includes legal comments
+    pub(crate) fn print_statement_comments(&mut self, start: u32) {
+        if let Some((comments, unused)) = self.get_statement_comments(start) {
+            self.print_comments(start, &comments, unused);
+        }
     }
 
     pub(crate) fn print_annotation_comments(&mut self, node_start: u32) {
@@ -162,7 +170,12 @@ impl<'a> Codegen<'a> {
         }
     }
 
-    fn print_comments(&mut self, start: u32, comments: &[Comment], unused_comments: Vec<Comment>) {
+    pub(crate) fn print_comments(
+        &mut self,
+        start: u32,
+        comments: &[Comment],
+        unused_comments: Vec<Comment>,
+    ) {
         for (i, comment) in comments.iter().enumerate() {
             if i == 0 {
                 if comment.preceded_by_newline {

crates/oxc_codegen/src/gen.rs

@@ -48,6 +48,8 @@ impl<'a> Gen for Program<'a> {
             stmt.print(p, ctx);
             p.print_semicolon_if_needed();
         }
+        // Print trailing statement comments.
+        p.print_statement_comments(self.span.end);
     }
 }
 
@@ -662,7 +664,18 @@ impl<'a> Gen for Function<'a> {
 
 impl<'a> Gen for FunctionBody<'a> {
     fn gen(&self, p: &mut Codegen, ctx: Context) {
-        p.print_curly_braces(self.span, self.is_empty(), |p| {
+        let span_end = self.span.end;
+        let comments_at_end = if !p.options.minify && span_end != 0 {
+            p.get_statement_comments(span_end - 1)
+        } else {
+            None
+        };
+        let is_empty = if self.is_empty() {
+            comments_at_end.is_none() || comments_at_end.as_ref().is_some_and(|c| c.0.is_empty())
+        } else {
+            false
+        };
+        p.print_curly_braces(self.span, is_empty, |p| {
             for directive in &self.directives {
                 directive.print(p, ctx);
             }
@@ -670,6 +683,10 @@ impl<'a> Gen for FunctionBody<'a> {
                 p.print_semicolon_if_needed();
                 stmt.print(p, ctx);
             }
+            // Print trailing statement comments.
+            if let Some((comments, unused)) = comments_at_end {
+                p.print_comments(span_end - 1, &comments, unused);
+            }
         });
         p.needs_semicolon = false;
     }

crates/oxc_codegen/tests/integration/legal_comments.rs

@@ -17,6 +17,23 @@ fn cases() -> Vec<&'static str> {
     bar;
 }",
         "function bar() { var foo; /*! #__NO_SIDE_EFFECTS__ */ function () { } }",
+        "function foo() {
+	(() => {
+		/**
+		 * @preserve
+		 */
+	})();
+	/**
+	 * @preserve
+	 */
+}
+/**
+ * @preserve
+ */",
+        "/**
+* @preserve
+*/
+",
     ]
 }
 

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

@@ -76,3 +76,41 @@ function bar() {
 	function() {}
 }
 /*! #__NO_SIDE_EFFECTS__ */
+
+########## 7
+function foo() {
+	(() => {
+		/**
+		 * @preserve
+		 */
+	})();
+	/**
+	 * @preserve
+	 */
+}
+/**
+ * @preserve
+ */
+----------
+function foo() {
+	(() => {
+		/**
+		* @preserve
+		*/
+	})();
+	/**
+	* @preserve
+	*/
+}
+/**
+* @preserve
+*/
+########## 8
+/**
+* @preserve
+*/
+
+----------
+/**
+* @preserve
+*/

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

@@ -75,3 +75,41 @@ function bar() {
 	var foo;
 	/*! #__NO_SIDE_EFFECTS__ */ function() {}
 }
+
+########## 7
+function foo() {
+	(() => {
+		/**
+		 * @preserve
+		 */
+	})();
+	/**
+	 * @preserve
+	 */
+}
+/**
+ * @preserve
+ */
+----------
+function foo() {
+	(() => {
+		/**
+		* @preserve
+		*/
+	})();
+	/**
+	* @preserve
+	*/
+}
+/**
+* @preserve
+*/
+########## 8
+/**
+* @preserve
+*/
+
+----------
+/**
+* @preserve
+*/

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

@@ -62,3 +62,41 @@ function bar() {
 	function() {}
 }
 /*! For license information please see test.js */
+########## 7
+function foo() {
+	(() => {
+		/**
+		 * @preserve
+		 */
+	})();
+	/**
+	 * @preserve
+	 */
+}
+/**
+ * @preserve
+ */
+----------
+function foo() {
+	(() => {
+		/**
+		* @preserve
+		*/
+	})();
+	/**
+	* @preserve
+	*/
+}
+/**
+* @preserve
+*//*! For license information please see test.js */
+########## 8
+/**
+* @preserve
+*/
+
+----------
+/**
+* @preserve
+*/
+/*! For license information please see test.js */