feat: make `preserveComments` effective in DOM renderer (#7182)

src/compiler/compile/render_dom/wrappers/Comment.ts

@@ -0,0 +1,41 @@
+import Renderer from '../Renderer';
+import Block from '../Block';
+import Comment from '../../nodes/Comment';
+import Wrapper from './shared/Wrapper';
+import { x } from 'code-red';
+import { Identifier } from 'estree';
+
+export default class CommentWrapper extends Wrapper {
+	node: Comment;
+	var: Identifier;
+
+	constructor(
+		renderer: Renderer,
+		block: Block,
+		parent: Wrapper,
+		node: Comment
+	) {
+		super(renderer, block, parent, node);
+		this.var = x`c` as Identifier;
+	}
+
+	render(block: Block, parent_node: Identifier, parent_nodes: Identifier) {
+	    if (!this.renderer.options.preserveComments) return;
+
+		const string_literal = {
+			type: 'Literal',
+			value: this.node.data,
+			loc: {
+				start: this.renderer.locate(this.node.start),
+				end: this.renderer.locate(this.node.end)
+			}
+		};
+
+		block.add_element(
+			this.var,
+			x`@comment(${string_literal})`,
+			parent_nodes && x`@claim_comment(${parent_nodes}, ${string_literal})`,
+			parent_node
+		);
+	}
+}

src/compiler/compile/render_dom/wrappers/Fragment.ts

@@ -14,6 +14,7 @@ import RawMustacheTag from './RawMustacheTag';
 import Slot from './Slot';
 import SlotTemplate from './SlotTemplate';
 import Text from './Text';
+import Comment from './Comment';
 import Title from './Title';
 import Window from './Window';
 import { INode } from '../../nodes/interfaces';
@@ -27,7 +28,7 @@ import { regex_starts_with_whitespace } from '../../../utils/patterns';
 const wrappers = {
 	AwaitBlock,
 	Body,
-	Comment: null,
+	Comment,
 	DebugTag,
 	Document,
 	EachBlock,
@@ -118,7 +119,7 @@ export default class FragmentWrapper {
 				link(last_child, last_child = wrapper);
 			} else {
 				const Wrapper = wrappers[child.type];
-				if (!Wrapper) continue;
+				if (!Wrapper || (child.type === 'Comment' && !renderer.options.preserveComments)) continue;
 
 				const wrapper = new Wrapper(renderer, block, parent, child, strip_whitespace, last_child || next_sibling);
 				this.nodes.unshift(wrapper);

src/runtime/internal/dom.ts

@@ -254,6 +254,10 @@ export function empty() {
 	return text('');
 }
 
+export function comment(content: string) {
+	return document.createComment(content);
+}
+
 export function listen(node: EventTarget, event: string, handler: EventListenerOrEventListenerObject, options?: boolean | AddEventListenerOptions | EventListenerOptions) {
 	node.addEventListener(event, handler, options);
 	return () => node.removeEventListener(event, handler, options);
@@ -550,6 +554,19 @@ export function claim_space(nodes) {
 	return claim_text(nodes, ' ');
 }
 
+export function claim_comment(nodes:ChildNodeArray, data) {
+	return claim_node<Comment>(
+		nodes,
+		(node: ChildNode): node is Comment => node.nodeType === 8,
+		(node: Comment) => {
+			node.data =  '' + data;
+			return undefined;
+		},
+		() => comment(data),
+		true
+	);
+}
+
 function find_comment(nodes, text, start) {
 	for (let i = start; i < nodes.length; i += 1) {
 		const node = nodes[i];

test/hydration/samples/claim-comment/_after.html

@@ -0,0 +1 @@
+<div><!-- test1 --><!-- test2 --></div>

test/hydration/samples/claim-comment/_before.html

@@ -0,0 +1 @@
+<div><!-- test1 --></div>

test/hydration/samples/claim-comment/_config.js

@@ -0,0 +1,20 @@
+export default {
+	compileOptions: {
+		preserveComments:true
+	},
+	snapshot(target) {
+		const div = target.querySelector('div');
+
+		return {
+			div,
+			comment: div.childNodes[0]
+		};
+	},
+
+	test(assert, target, snapshot) {
+		const div = target.querySelector('div');
+		assert.equal(div, snapshot.div);
+		assert.equal(div.childNodes[0], snapshot.comment);
+		assert.equal(div.childNodes[1].nodeType, 8);
+	}
+};

test/hydration/samples/claim-comment/main.svelte

@@ -0,0 +1 @@
+<div><!-- test1 --><!-- test2 --></div>

test/js/samples/dom-preserve-comments/_config.js

@@ -0,0 +1,5 @@
+export default {
+	options: {
+		preserveComments: true
+	}
+};

test/js/samples/dom-preserve-comments/expected.js

@@ -0,0 +1,58 @@
+/* generated by Svelte vX.Y.Z */
+import {
+	SvelteComponent,
+	comment,
+	detach,
+	element,
+	init,
+	insert,
+	noop,
+	safe_not_equal,
+	space
+} from "svelte/internal";
+
+function create_fragment(ctx) {
+	let div0;
+	let t1;
+	let c;
+	let t2;
+	let div1;
+
+	return {
+		c() {
+			div0 = element("div");
+			div0.textContent = "content";
+			t1 = space();
+			c = comment(" comment ");
+			t2 = space();
+			div1 = element("div");
+			div1.textContent = "more content";
+		},
+		m(target, anchor) {
+			insert(target, div0, anchor);
+			insert(target, t1, anchor);
+			insert(target, c, anchor);
+			insert(target, t2, anchor);
+			insert(target, div1, anchor);
+		},
+		p: noop,
+		i: noop,
+		o: noop,
+		d(detaching) {
+			if (detaching) detach(div0);
+			if (detaching) detach(t1);
+			if (detaching) detach(c);
+			if (detaching) detach(t2);
+			if (detaching) detach(div1);
+		}
+	};
+}
+
+class Component extends SvelteComponent {
+	constructor(options) {
+		super();
+		init(this, options, null, create_fragment, safe_not_equal, {});
+	}
+}
+
+export default Component;

test/js/samples/dom-preserve-comments/input.svelte

@@ -0,0 +1,3 @@
+<div>content</div>
+<!-- comment -->
+<div>more content</div>