escape @ sigils in dev tooling events (sveltejs#3545)

Author: Conduitry

src/compiler/compile/render_dom/Block.ts

@@ -2,7 +2,7 @@ import CodeBuilder from '../utils/CodeBuilder';
 import deindent from '../utils/deindent';
 import Renderer from './Renderer';
 import Wrapper from './wrappers/shared/Wrapper';
-import { escape } from '../utils/stringify';
+import { stringify, escape } from '../utils/stringify';
 
 export interface BlockOptions {
 	parent?: Block;
@@ -378,7 +378,7 @@ export default class Block {
 					const block = {
 						${properties}
 					};
-					@dispatch_dev("SvelteRegisterBlock", { block, id: ${this.name || 'create_fragment'}.name, type: "${this.type}", source: "${this.comment ? this.comment.replace(/"/g, '\\"') : ''}", ctx });
+					@dispatch_dev("SvelteRegisterBlock", { block, id: ${this.name || 'create_fragment'}.name, type: "${this.type}", source: ${stringify(this.comment || '', { only_escape_at_symbol: true })}, ctx });
 					return block;`
 				: deindent`
 					return {

test/runtime/samples/sigil-component-attribute/Widget.svelte test/runtime/samples/sigil-component-prop/Widget.svelte

@@ -1,4 +1,7 @@
 export default {
+	compileOptions: {
+		dev: true
+	},
 	props: { foo: 'foo' },
 	html: `<div>foo @ foo # foo</div>`,
 };

test/runtime/samples/sigil-component-attribute/_config.js test/runtime/samples/sigil-component-prop/_config.js

@@ -3,4 +3,5 @@
 	export let foo;
 </script>
 
-<Widget value='foo @ {foo} # foo'/>
+<Widget value='foo @ {foo} # foo'>
+</Widget>