Keep leading comments on consecutive lines (#4975)

src/ast/nodes/Program.ts

@@ -3,7 +3,11 @@ import type MagicString from 'magic-string';
 import getCodeFrame from '../../utils/getCodeFrame';
 import { getOriginalLocation } from '../../utils/getOriginalLocation';
 import relativeId from '../../utils/relativeId';
-import { type RenderOptions, renderStatementList } from '../../utils/renderHelpers';
+import {
+	findFirstLineBreakOutsideComment,
+	type RenderOptions,
+	renderStatementList
+} from '../../utils/renderHelpers';
 import type { HasEffectsContext, InclusionContext } from '../ExecutionContext';
 import { createHasEffectsContext } from '../ExecutionContext';
 import type * as NodeType from './NodeType';
@@ -79,6 +83,16 @@ export default class Program extends NodeBase {
 			code.remove(0, start);
 		}
 		if (this.body.length > 0) {
+			// Keep all consecutive lines that start with a comment
+			while (code.original[start] === '/' && /[*/]/.test(code.original[start + 1])) {
+				const firstLineBreak = findFirstLineBreakOutsideComment(
+					code.original.slice(start, this.body[0].start)
+				);
+				if (firstLineBreak[0] === -1) {
+					break;
+				}
+				start += firstLineBreak[1];
+			}
 			renderStatementList(this.body, code, start, this.end, options);
 		} else {
 			super.render(code, options);

src/utils/renderHelpers.ts

@@ -70,7 +70,7 @@ export function findNonWhiteSpace(code: string, index: number): number {
 
 // This assumes "code" only contains white-space and comments
 // Returns position of line-comment if applicable
-function findFirstLineBreakOutsideComment(code: string): [number, number] {
+export function findFirstLineBreakOutsideComment(code: string): [number, number] {
 	let lineBreakPos,
 		charCodeAfterSlash,
 		start = 0;

test/form/samples/leading-comments/_config.js

@@ -0,0 +1,6 @@
+module.exports = defineTest({
+	description: 'keeps leading comments on consecutive lines',
+	options: {
+		external: ['external']
+	}
+});

test/form/samples/leading-comments/_expected.js

@@ -0,0 +1,13 @@
+import 'external';
+
+// comment dep 1/3
+/* comment
+*/ // comment dep 2/3
+// comment dep 3/3
+
+console.log('dep');
+
+// comment main 1/2
+// comment main 2/2
+
+console.log('main');

test/form/samples/leading-comments/dep.js

@@ -0,0 +1,7 @@
+// comment dep 1/3
+/* comment
+*/ // comment dep 2/3
+// comment dep 3/3
+/* import comment */ import 'external';
+
+console.log('dep');

test/form/samples/leading-comments/main.js

@@ -0,0 +1,6 @@
+#! /usr/bin/env node
+// comment main 1/2
+// comment main 2/2
+import './dep.js';
+
+console.log('main');

test/form/samples/pure-comment-scenarios-complex/_expected.js

@@ -1,5 +1,6 @@
 // pure top-level IIFE will be dropped
 
+
 // pure top-level IIFE assigned to unreferenced var will not be dropped
 global.iife1 = /*@__PURE__*/(function() {
 	console.log("iife1");

test/form/samples/remove-treeshaken-banners/_expected.js

@@ -1,4 +1,5 @@
 // dep included banner: included
+
 console.log('dep included');
 
 // dep included footer: included

test/form/samples/render-removed-statements/_expected.js

@@ -1,4 +1,5 @@
 /* header retained */
+
  /* lead
 retained */ console.log(2); // trail retained
 console.log(2); // trail retained