get leading comment back

Author: Austaras

crates/swc_ecma_minifier/src/lib.rs

@@ -40,7 +40,9 @@
 
 use once_cell::sync::Lazy;
 use pass::mangle_names::mangle_names;
-use swc_common::{comments::Comments, pass::Repeated, sync::Lrc, SourceMap, SyntaxContext};
+use swc_common::{
+    comments::Comments, pass::Repeated, sync::Lrc, SourceMap, Spanned, SyntaxContext,
+};
 use swc_ecma_ast::*;
 use swc_ecma_transforms_optimization::debug_assert_valid;
 use swc_ecma_usage_analyzer::marks::Marks;
@@ -157,6 +159,11 @@ pub fn optimize(
         {
             let _timer = timer!("compress ast");
 
+            let first_span = match &n {
+                Program::Module(module) => module.body.first().map(|s| s.span()),
+                Program::Script(script) => script.body.first().map(|s| s.span()),
+            };
+
             perform_dce(&mut n, c, marks);
 
             n.mutate(&mut compressor(
@@ -167,6 +174,22 @@ pub fn optimize(
             ));
 
             perform_dce(&mut n, c, marks);
+
+            let new_first_span = match &n {
+                Program::Module(module) => module.body.first().map(|s| s.span()),
+                Program::Script(script) => script.body.first().map(|s| s.span()),
+            };
+
+            if first_span.map(|s| s.lo) != new_first_span.map(|s| s.lo) {
+                if let (Some(span), Some(comments)) = (first_span, comments) {
+                    let comment = comments.take_leading(span.lo);
+                    let new_pos = new_first_span.unwrap_or(n.span()).lo;
+
+                    for cmt in comment.into_iter().flatten() {
+                        comments.add_leading(new_pos, cmt);
+                    }
+                }
+            }
         }
 
         // Again, we don't need to validate ast

crates/swc_ecma_minifier/tests/benches-full/lodash.js

@@ -1,4 +1,11 @@
-(function() {
+/**
+ * @license
+ * Lodash <https://lodash.com/>
+ * Copyright OpenJS Foundation and other contributors <https://openjsf.org/>
+ * Released under MIT license <https://lodash.com/license>
+ * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
+ * Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
+ */ (function() {
     /** Error message constants. */ var undefined, FUNC_ERROR_TEXT = 'Expected a function', HASH_UNDEFINED = '__lodash_hash_undefined__', PLACEHOLDER = '__lodash_placeholder__', INFINITY = 1 / 0, NAN = 0 / 0, wrapFlags = [
         [
             'ary',

crates/swc_ecma_minifier/tests/benches-full/moment.js

@@ -1,3 +1,8 @@
+//! moment.js
+//! version : 2.29.1
+//! authors : Tim Wood, Iskren Chernev, Moment.js contributors
+//! license : MIT
+//! momentjs.com
 !function(global, factory) {
     'object' == typeof exports && 'undefined' != typeof module ? module.exports = factory() : 'function' == typeof define && define.amd ? define(factory) : global.moment = factory();
 }(this, function() {

crates/swc_ecma_minifier/tests/fixture/issues/10054/for/output.js

@@ -1,3 +1,4 @@
+// Input:
 window.a = [
     function() {
         for(var l = 0; i < 10; l++);

crates/swc_ecma_minifier/tests/fixture/issues/10054/if/output.js

@@ -1,3 +1,4 @@
+// Input:
 window.a = [
     function() {
         if (void 0 !== navigator.userAgentData) throw Error();

crates/swc_ecma_minifier/tests/fixture/issues/10178/output.js

@@ -0,0 +1 @@
+//// [indexerWithTuple.ts]

crates/swc_ecma_minifier/tests/fixture/issues/10539/output.js

@@ -1,4 +1,5 @@
 // class def disappears, leaving only `new DoesntWorkClass()` as output
+// class def completely disappears
 (class DoesntWorkClass {
     static prop = new DoesntWorkClass();
 });

crates/swc_ecma_minifier/tests/fixture/issues/3256/2/output.js

@@ -1,3 +1,4 @@
+// real life example taken from https://github.com/nodeca/pako/blob/master/lib/zlib/adler32.js#L26
 export default ((adler, buf, len, pos)=>{
     let s1 = 0xffff & adler, s2 = adler >>> 16 & 0xffff, n = 0;
     for(; 0 !== len;){

crates/swc_ecma_minifier/tests/fixture/issues/emotion/react/2/output.js

@@ -1,4 +1,4 @@
-var fn, cache, cursor, hyphenateRegex = /[A-Z]|^ms/g, animationRegex = /_EMO_([^_]+?)_([^]*?)_EMO_/g, unitless_browser_esm = {
+/* harmony default export */ var fn, cache, cursor, hyphenateRegex = /[A-Z]|^ms/g, animationRegex = /_EMO_([^_]+?)_([^]*?)_EMO_/g, unitless_browser_esm = {
     animationIterationCount: 1,
     borderImageOutset: 1,
     borderImageSlice: 1,