fix: preserve CSS comments in the AST printer (#18637)

Adds a new `comments` array to the stylesheet node which CSS comments
are added to. Is subsequently used in `print` to see them in the output.

Alternative to #18475

.changeset/soft-cats-comment.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: preserve CSS comments in the AST printer

packages/svelte/src/compiler/index.js

@@ -141,7 +141,8 @@ export function parseCss(source) {
 		type: 'StyleSheetFile',
 		start: 0,
 		end: source.length,
-		children
+		children,
+		comments: parser.css_comments
 	};
 }
 

packages/svelte/src/compiler/phases/1-parse/index.js

@@ -50,6 +50,9 @@ export class Parser {
 	/** */
 	index = 0;
 
+	/** @type {AST.CSS.CSSComment[]} */
+	css_comments = [];
+
 	/**
 	 * Creates a minimal parser instance for CSS-only parsing.
 	 * Skips Svelte component parsing setup.
@@ -61,6 +64,7 @@ export class Parser {
 		parser.template = source;
 		parser.index = 0;
 		parser.loose = false;
+		parser.css_comments = [];
 		return parser;
 	}
 

packages/svelte/src/compiler/phases/1-parse/read/style.js

@@ -24,6 +24,7 @@ const REGEX_HTML_COMMENT_CLOSE = /-->/;
  */
 export default function read_style(parser, start, attributes) {
 	const content_start = parser.index;
+	parser.css_comments = [];
 	const children = read_body(parser, (p) => p.match('</style') || p.index >= p.template.length);
 	const content_end = parser.index;
 
@@ -36,6 +37,7 @@ export default function read_style(parser, start, attributes) {
 		end: parser.index,
 		attributes,
 		children,
+		comments: parser.css_comments,
 		content: {
 			start: content_start,
 			end: content_end,
@@ -229,18 +231,22 @@ function read_selector(parser, inside_pseudo_class = false) {
 				end: parser.index
 			});
 		} else if (parser.eat('::')) {
+			const name = read_identifier(parser);
+			/** @type {AST.CSS.SelectorList | null} */
+			let args = null;
+
+			if (parser.eat('(')) {
+				args = read_selector_list(parser, true);
+				parser.eat(')', true);
+			}
+
 			relative_selector.selectors.push({
 				type: 'PseudoElementSelector',
-				name: read_identifier(parser),
+				name,
 				start,
-				end: parser.index
+				end: parser.index,
+				...(args && { args })
 			});
-			// We read the inner selectors of a pseudo element to ensure it parses correctly,
-			// but we don't do anything with the result.
-			if (parser.eat('(')) {
-				read_selector_list(parser, true);
-				parser.eat(')', true);
-			}
 		} else if (parser.eat(':')) {
 			const name = read_identifier(parser);
 
@@ -323,7 +329,7 @@ function read_selector(parser, inside_pseudo_class = false) {
 		}
 
 		const index = parser.index;
-		allow_comment_or_whitespace(parser);
+		allow_comment_or_whitespace(parser, false);
 
 		if (parser.match(',') || (inside_pseudo_class ? parser.match(')') : parser.match('{'))) {
 			// rewind, so we know whether to continue building the selector list
@@ -449,7 +455,7 @@ function read_block_item(parser) {
 	// read ahead to understand whether we're dealing with a declaration or a nested rule.
 	// this involves some duplicated work, but avoids a try-catch that would disguise errors
 	const start = parser.index;
-	read_value(parser);
+	read_value(parser, false);
 	const char = parser.template[parser.index];
 	parser.index = start;
 
@@ -492,10 +498,13 @@ function read_declaration(parser) {
 
 /**
  * @param {Parser} parser
+ * @param {boolean} [capture_comments]
  * @returns {string}
  */
-function read_value(parser) {
+function read_value(parser, capture_comments = true) {
 	let value = '';
+	/** @type {AST.CSS.CSSComment[]} */
+	const value_comments = [];
 	let escaped = false;
 	let in_url = false;
 
@@ -523,6 +532,13 @@ function read_value(parser) {
 		} else if (char === '(' && value.slice(-3) === 'url') {
 			in_url = true;
 		} else if ((char === ';' || char === '{' || char === '}') && !in_url && !quote_mark) {
+			const leading_whitespace = value.length - value.trimStart().length;
+			for (const comment of value_comments) {
+				comment.position = Math.max(
+					0,
+					/** @type {number} */ (comment.position) - leading_whitespace
+				);
+			}
 			return value.trim();
 		} else if (
 			char === '/' &&
@@ -530,13 +546,11 @@ function read_value(parser) {
 			!quote_mark &&
 			parser.template[parser.index + 1] === '*'
 		) {
-			parser.index += 2;
+			const comment = read_comment(parser);
-			while (parser.index < parser.template.length) {
+			if (capture_comments) {
-				if (parser.template[parser.index] === '*' && parser.template[parser.index + 1] === '/') {
+				comment.position = value.length;
-					parser.index += 2;
+				parser.css_comments.push(comment);
-					break;
+				value_comments.push(comment);
-				}
-				parser.index++;
 			}
 			continue;
 		}
@@ -624,13 +638,16 @@ function read_identifier(parser) {
 	return identifier;
 }
 
-/** @param {Parser} parser */
+/**
-function allow_comment_or_whitespace(parser) {
+ * @param {Parser} parser
+ * @param {boolean} [capture_comments]
+ */
+function allow_comment_or_whitespace(parser, capture_comments = true) {
 	parser.allow_whitespace();
 	while (parser.match('/*') || parser.match('<!--')) {
-		if (parser.eat('/*')) {
+		if (parser.match('/*')) {
-			parser.read_until(REGEX_COMMENT_CLOSE);
+			const comment = read_comment(parser);
-			parser.eat('*/', true);
+			if (capture_comments) parser.css_comments.push(comment);
 		}
 
 		if (parser.eat('<!--')) {
@@ -642,6 +659,25 @@ function allow_comment_or_whitespace(parser) {
 	}
 }
 
+/**
+ * @param {Parser} parser
+ * @returns {AST.CSS.CSSComment}
+ */
+function read_comment(parser) {
+	const start = parser.index;
+	parser.eat('/*', true);
+	const value = parser.read_until(REGEX_COMMENT_CLOSE);
+	parser.eat('*/', true);
+	const end = parser.index;
+
+	return {
+		type: 'CSSComment',
+		value,
+		start,
+		end
+	};
+}
+
 /**
  * Parse standalone CSS content (not wrapped in `<style>`).
  * @param {Parser} parser

packages/svelte/src/compiler/phases/2-analyze/css/css-analyze.js

@@ -312,6 +312,9 @@ const css_visitors = {
 		}
 
 		context.next();
+	},
+	PseudoElementSelector() {
+		// Don't analyse these
 	}
 };
 

packages/svelte/src/compiler/phases/2-analyze/css/css-warn.js

@@ -23,6 +23,9 @@ const visitors = {
 			context.next();
 		}
 	},
+	PseudoElementSelector() {
+		// Don't analyse these
+	},
 	ComplexSelector(node, context) {
 		if (
 			!node.metadata.used &&

packages/svelte/src/compiler/phases/3-transform/css/index.js

@@ -374,6 +374,9 @@ const visitors = {
 		if (node.name === 'is' || node.name === 'where' || node.name === 'has' || node.name === 'not') {
 			context.next();
 		}
+	},
+	PseudoElementSelector() {
+		// Functional pseudo-element arguments are not scoped as selectors.
 	}
 };
 

packages/svelte/src/compiler/print/index.js

@@ -19,6 +19,9 @@ const LINE_BREAK_THRESHOLD = 50;
  */
 export function print(ast, options = undefined) {
 	const comments = (ast.type === 'Root' && ast.comments) || [];
+	const css_comments =
+		(ast.type === 'Root' ? ast.css?.comments : ast.type === 'StyleSheet' ? ast.comments : null) ||
+		[];
 
 	return esrap.print(
 		ast,
@@ -29,7 +32,7 @@ export function print(ast, options = undefined) {
 				getTrailingComments: options?.getTrailingComments
 			}),
 			...svelte_visitors(comments),
-			...css_visitors
+			...css_visitors(css_comments, comments)
 		}),
 		{
 			indent: options?.indent
@@ -177,11 +180,132 @@ function base_element(node, context, comments) {
 	context.append(child_context);
 }
 
-/** @type {Visitors<AST.SvelteNode>} */
+/**
-const css_visitors = {
+ * @param {AST.CSS.CSSComment[]} comments
+ * @param {AST.JSComment[]} js_comments
+ * @returns {Visitors<AST.SvelteNode>}
+ */
+function css_visitors(comments, js_comments) {
+	let comment_index = 0;
+
+	/** @param {number} end */
+	const has_comment_before = (end) => comments[comment_index]?.start < end;
+
+	/**
+	 * @param {Context} context
+	 * @param {AST.CSS.CSSComment} comment
+	 */
+	function write_comment(context, comment) {
+		context.write(`/*${comment.value}*/`);
+	}
+
+	/**
+	 * @param {Context} context
+	 * @param {number} end
+	 */
+	function write_inline_comments(context, end) {
+		let written = false;
+
+		while (has_comment_before(end)) {
+			if (written) context.write(' ');
+			write_comment(context, comments[comment_index++]);
+			written = true;
+		}
+
+		return written;
+	}
+
+	/**
+	 * @param {Context} context
+	 * @param {string} value
+	 * @param {number} end
+	 */
+	function write_value(context, value, end) {
+		let offset = 0;
+
+		while (has_comment_before(end)) {
+			const comment = comments[comment_index++];
+			const position = Math.max(offset, Math.min(comment.position ?? 0, value.length));
+			context.write(value.slice(offset, position));
+			write_comment(context, comment);
+			offset = position;
+		}
+
+		context.write(value.slice(offset));
+	}
+
+	/**
+	 * @param {Context} context
+	 * @param {Array<AST.CSS.Rule | AST.CSS.Atrule | AST.CSS.Declaration>} children
+	 * @param {number} end
+	 * @param {boolean} margins
+	 */
+	function print_children(context, children, end, margins) {
+		let started = false;
+
+		const separate = () => {
+			if (!started) return;
+			if (margins) context.margin();
+			context.newline();
+		};
+
+		for (const child of children) {
+			while (has_comment_before(child.start)) {
+				separate();
+				write_comment(context, comments[comment_index++]);
+				started = true;
+			}
+
+			separate();
+			context.visit(child);
+			started = true;
+		}
+
+		while (has_comment_before(end)) {
+			separate();
+			write_comment(context, comments[comment_index++]);
+			started = true;
+		}
+	}
+
+	/**
+	 * @param {AST.CSS.SelectorList} node
+	 * @param {Context} context
+	 * @param {boolean} multiline
+	 */
+	function print_selector_list(node, context, multiline) {
+		let needs_separator = false;
+		let remaining_selectors = node.children.length;
+
+		for (const selector of node.children) {
+			while (has_comment_before(selector.start)) {
+				if (needs_separator) context.write(' ');
+				write_comment(context, comments[comment_index++]);
+				needs_separator = true;
+			}
+
+			if (needs_separator) {
+				if (multiline) context.newline();
+				else context.write(' ');
+			}
+
+			context.visit(selector);
+			needs_separator = true;
+			remaining_selectors -= 1;
+
+			if (remaining_selectors > 0) context.write(',');
+		}
+	}
+
+	return {
 		Atrule(node, context) {
 			context.write(`@${node.name}`);
-		if (node.prelude) context.write(` ${node.prelude}`);
+
+			const prelude_end = node.block?.start ?? node.end;
+			if (node.prelude || has_comment_before(prelude_end)) {
+				context.write(' ');
+				write_value(context, node.prelude, prelude_end);
+			}
 
 			if (node.block) {
 				context.write(' ');
@@ -196,9 +320,7 @@ const css_visitors = {
 			if (node.matcher) {
 				context.write(node.matcher);
 				context.write(`"${node.value}"`);
-			if (node.flags) {
+				if (node.flags) context.write(` ${node.flags}`);
-				context.write(` ${node.flags}`);
-			}
 			}
 			context.write(']');
 		},
@@ -206,22 +328,10 @@ const css_visitors = {
 		Block(node, context) {
 			context.write('{');
 
-		if (node.children.length > 0) {
+			if (node.children.length > 0 || has_comment_before(node.end)) {
 				context.indent();
 				context.newline();
-
+				print_children(context, node.children, node.end, false);
-			let started = false;
-
-			for (const child of node.children) {
-				if (started) {
-					context.newline();
-				}
-
-				context.visit(child);
-
-				started = true;
-			}
-
 				context.dedent();
 				context.newline();
 			}
@@ -234,13 +344,13 @@ const css_visitors = {
 		},
 
 		ComplexSelector(node, context) {
-		for (const selector of node.children) {
+			for (const selector of node.children) context.visit(selector);
-			context.visit(selector);
-		}
 		},
 
 		Declaration(node, context) {
-		context.write(`${node.property}: ${node.value};`);
+			context.write(`${node.property}: `);
+			write_value(context, node.value, node.end);
+			context.write(';');
 		},
 
 		IdSelector(node, context) {
@@ -264,74 +374,69 @@ const css_visitors = {
 
 			if (node.args) {
 				context.write('(');
-
+				context.visit(node.args);
-			let started = false;
+				if (has_comment_before(node.end)) {
-
+					context.write(' ');
-			for (const arg of node.args.children) {
+					write_inline_comments(context, node.end);
-				if (started) {
-					context.write(', ');
-				}
-
-				context.visit(arg);
-
-				started = true;
 				}
-
 				context.write(')');
 			}
 		},
 
 		PseudoElementSelector(node, context) {
 			context.write(`::${node.name}`);
+			if (node.args) {
+				context.write('(');
+				context.visit(node.args);
+				if (has_comment_before(node.end)) {
+					context.write(' ');
+					write_inline_comments(context, node.end);
+				}
+				context.write(')');
+			}
 		},
 
 		RelativeSelector(node, context) {
 			if (node.combinator) {
-			if (node.combinator.name === ' ') {
+				if (node.combinator.name === ' ') context.write(' ');
-				context.write(' ');
+				else context.write(` ${node.combinator.name} `);
-			} else {
-				context.write(` ${node.combinator.name} `);
-			}
 			}
 
-		for (const selector of node.selectors) {
+			for (const selector of node.selectors) context.visit(selector);
-			context.visit(selector);
-		}
 		},
 
 		Rule(node, context) {
-		let started = false;
+			print_selector_list(node.prelude, context, true);
-
-		for (const selector of node.prelude.children) {
-			if (started) {
-				context.write(',');
-				context.newline();
-			}
-
-			context.visit(selector);
-			started = true;
-		}
-
 			context.write(' ');
+			if (write_inline_comments(context, node.block.start)) context.write(' ');
 			context.visit(node.block);
 		},
 
 		SelectorList(node, context) {
-		let started = false;
+			print_selector_list(node, context, false);
-		for (const selector of node.children) {
+		},
-			if (started) {
-				context.write(', ');
-			}
 
-			context.visit(selector);
+		StyleSheet(node, context) {
-			started = true;
+			context.write('<style');
+			attributes(node, node.attributes, context, js_comments);
+			context.write('>');
+
+			if (node.children.length > 0 || node.comments.length > 0) {
+				context.indent();
+				context.newline();
+				print_children(context, node.children, node.content.end, true);
+				context.dedent();
+				context.newline();
 			}
+
+			context.write('</style>');
 		},
 
 		TypeSelector(node, context) {
 			context.write(node.name);
 		}
 	};
+}
 
 /**
  * @param {AST.JSComment[]} comments
@@ -845,34 +950,6 @@ const svelte_visitors = (comments) => ({
 		}
 	},
 
-	StyleSheet(node, context) {
-		context.write('<style');
-		attributes(node, node.attributes, context, comments);
-		context.write('>');
-
-		if (node.children.length > 0) {
-			context.indent();
-			context.newline();
-
-			let started = false;
-
-			for (const child of node.children) {
-				if (started) {
-					context.margin();
-					context.newline();
-				}
-
-				context.visit(child);
-				started = true;
-			}
-
-			context.dedent();
-			context.newline();
-		}
-
-		context.write('</style>');
-	},
-
 	SvelteBody(node, context) {
 		base_element(node, context, comments);
 	},

packages/svelte/src/compiler/types/css.d.ts

@@ -8,6 +8,15 @@ export namespace _CSS {
 
 	export interface StyleSheetBase extends BaseNode {
 		children: Array<Atrule | Rule>;
+		/** CSS comments in source order */
+		comments: CSSComment[];
+	}
+
+	export interface CSSComment extends BaseNode {
+		type: 'CSSComment';
+		value: string;
+		/** Character offset in a containing declaration value or at-rule prelude */
+		position?: number;
 	}
 
 	export interface StyleSheetFile extends StyleSheetBase {
@@ -135,6 +144,7 @@ export namespace _CSS {
 	export interface PseudoElementSelector extends BaseNode {
 		type: 'PseudoElementSelector';
 		name: string;
+		args?: SelectorList;
 	}
 
 	export interface PseudoClassSelector extends BaseNode {

packages/svelte/tests/css-parse.test.ts

@@ -69,9 +69,21 @@ describe('parseCss', () => {
 	});
 
 	it('parses comments', () => {
-		const ast = parseCss('/* comment */ div { color: red; }');
+		const ast = parseCss(
+			'/* top */ div, /* selector */ span { /* block */ color: /* value */ red; }'
+		);
 		assert.equal(ast.children.length, 1);
 		assert.equal(ast.children[0].type, 'Rule');
+		assert.deepEqual(
+			ast.comments.map((comment) => comment.value),
+			[' top ', ' selector ', ' block ', ' value ']
+		);
+		assert.deepEqual(ast.comments[0], {
+			type: 'CSSComment',
+			value: ' top ',
+			start: 0,
+			end: 9
+		});
 	});
 
 	it('parses complex selectors', () => {

packages/svelte/tests/parser-legacy/samples/css/output.json

@@ -33,6 +33,7 @@
 		"type": "Style",
 		"start": 16,
 		"end": 56,
+		"comments": [],
 		"attributes": [],
 		"children": [
 			{

packages/svelte/tests/parser-legacy/samples/whitespace-after-style-tag/output.json

@@ -33,6 +33,7 @@
 		"type": "Style",
 		"start": 16,
 		"end": 66,
+		"comments": [],
 		"attributes": [],
 		"children": [
 			{

packages/svelte/tests/parser-modern/samples/css-nth-syntax/output.json

@@ -1071,6 +1071,14 @@
 				"end": 797
 			}
 		],
+		"comments": [
+			{
+				"type": "CSSComment",
+				"value": " test that all these are parsed correctly ",
+				"start": 12,
+				"end": 58
+			}
+		],
 		"content": {
 			"start": 7,
 			"end": 798,
@@ -1125,5 +1133,6 @@
 			}
 		]
 	},
-	"options": null
+	"options": null,
+	"comments": []
 }

packages/svelte/tests/parser-modern/samples/css-pseudo-classes/output.json

@@ -25,7 +25,35 @@
 											"type": "PseudoElementSelector",
 											"name": "view-transition-old",
 											"start": 60,
-											"end": 81
+											"end": 86,
+											"args": {
+												"type": "SelectorList",
+												"start": 82,
+												"end": 85,
+												"children": [
+													{
+														"type": "ComplexSelector",
+														"start": 82,
+														"end": 85,
+														"children": [
+															{
+																"type": "RelativeSelector",
+																"combinator": null,
+																"selectors": [
+																	{
+																		"type": "TypeSelector",
+																		"name": "x-y",
+																		"start": 82,
+																		"end": 85
+																	}
+																],
+																"start": 82,
+																"end": 85
+															}
+														]
+													}
+												]
+											}
 										}
 									],
 									"start": 60,
@@ -89,7 +117,35 @@
 																		"type": "PseudoElementSelector",
 																		"name": "view-transition-old",
 																		"start": 119,
-																		"end": 140
+																		"end": 145,
+																		"args": {
+																			"type": "SelectorList",
+																			"start": 141,
+																			"end": 144,
+																			"children": [
+																				{
+																					"type": "ComplexSelector",
+																					"start": 141,
+																					"end": 144,
+																					"children": [
+																						{
+																							"type": "RelativeSelector",
+																							"combinator": null,
+																							"selectors": [
+																								{
+																									"type": "TypeSelector",
+																									"name": "x-y",
+																									"start": 141,
+																									"end": 144
+																								}
+																							],
+																							"start": 141,
+																							"end": 144
+																						}
+																					]
+																				}
+																			]
+																		}
 																	}
 																],
 																"start": 119,
@@ -147,7 +203,35 @@
 											"type": "PseudoElementSelector",
 											"name": "highlight",
 											"start": 171,
-											"end": 182
+											"end": 199,
+											"args": {
+												"type": "SelectorList",
+												"start": 183,
+												"end": 198,
+												"children": [
+													{
+														"type": "ComplexSelector",
+														"start": 183,
+														"end": 198,
+														"children": [
+															{
+																"type": "RelativeSelector",
+																"combinator": null,
+																"selectors": [
+																	{
+																		"type": "TypeSelector",
+																		"name": "rainbow-color-1",
+																		"start": 183,
+																		"end": 198
+																	}
+																],
+																"start": 183,
+																"end": 198
+															}
+														]
+													}
+												]
+											}
 										}
 									],
 									"start": 171,
@@ -200,7 +284,35 @@
 											"type": "PseudoElementSelector",
 											"name": "part",
 											"start": 234,
-											"end": 240
+											"end": 245,
+											"args": {
+												"type": "SelectorList",
+												"start": 241,
+												"end": 244,
+												"children": [
+													{
+														"type": "ComplexSelector",
+														"start": 241,
+														"end": 244,
+														"children": [
+															{
+																"type": "RelativeSelector",
+																"combinator": null,
+																"selectors": [
+																	{
+																		"type": "TypeSelector",
+																		"name": "foo",
+																		"start": 241,
+																		"end": 244
+																	}
+																],
+																"start": 241,
+																"end": 244
+															}
+														]
+													}
+												]
+											}
 										}
 									],
 									"start": 220,
@@ -247,7 +359,35 @@
 											"type": "PseudoElementSelector",
 											"name": "slotted",
 											"start": 266,
-											"end": 275
+											"end": 285,
+											"args": {
+												"type": "SelectorList",
+												"start": 276,
+												"end": 284,
+												"children": [
+													{
+														"type": "ComplexSelector",
+														"start": 276,
+														"end": 284,
+														"children": [
+															{
+																"type": "RelativeSelector",
+																"combinator": null,
+																"selectors": [
+																	{
+																		"type": "ClassSelector",
+																		"name": "content",
+																		"start": 276,
+																		"end": 284
+																	}
+																],
+																"start": 276,
+																"end": 284
+															}
+														]
+													}
+												]
+											}
 										}
 									],
 									"start": 266,
@@ -390,6 +530,26 @@
 				"end": 377
 			}
 		],
+		"comments": [
+			{
+				"type": "CSSComment",
+				"value": " test that all these are parsed correctly ",
+				"start": 12,
+				"end": 58
+			},
+			{
+				"type": "CSSComment",
+				"value": "button",
+				"start": 311,
+				"end": 321
+			},
+			{
+				"type": "CSSComment",
+				"value": "p after h1",
+				"start": 332,
+				"end": 346
+			}
+		],
 		"content": {
 			"start": 7,
 			"end": 378,
@@ -405,5 +565,6 @@
 		"type": "Fragment",
 		"nodes": []
 	},
-	"options": null
+	"options": null,
+	"comments": []
 }

packages/svelte/tests/parser-modern/samples/script-style-no-markup/output.json

@@ -53,6 +53,7 @@
 				"end": 82
 			}
 		],
+		"comments": [],
 		"content": {
 			"start": 61,
 			"end": 83,
@@ -77,6 +78,24 @@
 		]
 	},
 	"options": null,
+	"comments": [
+		{
+			"type": "Line",
+			"value": " script and style but no markup",
+			"start": 10,
+			"end": 43,
+			"loc": {
+				"start": {
+					"line": 2,
+					"column": 1
+				},
+				"end": {
+					"line": 2,
+					"column": 34
+				}
+			}
+		}
+	],
 	"instance": {
 		"type": "Script",
 		"start": 0,

packages/svelte/tests/parser-modern/samples/semicolon-inside-quotes/output.json

@@ -68,6 +68,7 @@
 				"end": 196
 			}
 		],
+		"comments": [],
 		"content": {
 			"start": 43,
 			"end": 197,
@@ -122,5 +123,6 @@
 			}
 		]
 	},
-	"options": null
+	"options": null,
+	"comments": []
 }

packages/svelte/tests/print/samples/style-comments/input.svelte

@@ -0,0 +1,26 @@
+<style>
+	/* first */
+	/* second */
+	.foo, /* between */
+	.bar /* trailing */ {
+		/* block */
+		color: r /* value */ ed;
+	}
+
+	@media screen/* media */and (width > 0) {
+		/* nested */
+		.baz {
+			display: block;
+		}
+	}
+
+	.empty {
+		/* only */
+	}
+
+	.part::part(/* argument */ label) {
+		display: block;
+	}
+
+	/* last */
+</style>

packages/svelte/tests/print/samples/style-comments/output.svelte

@@ -0,0 +1,28 @@
+<style>
+	/* first */
+
+	/* second */
+
+	.foo, /* between */
+	.bar /* trailing */ {
+		/* block */
+		color: r /* value */ ed;
+	}
+
+	@media screen/* media */and (width > 0) {
+		/* nested */
+		.baz {
+			display: block;
+		}
+	}
+
+	.empty {
+		/* only */
+	}
+
+	.part::part(/* argument */ label) {
+		display: block;
+	}
+
+	/* last */
+</style>

packages/svelte/types/index.d.ts

@@ -1694,6 +1694,15 @@ declare module 'svelte/compiler' {
 
 		export interface StyleSheetBase extends BaseNode {
 			children: Array<Atrule | Rule>;
+			/** CSS comments in source order */
+			comments: CSSComment[];
+		}
+
+		export interface CSSComment extends BaseNode {
+			type: 'CSSComment';
+			value: string;
+			/** Character offset in a containing declaration value or at-rule prelude */
+			position?: number;
 		}
 
 		export interface StyleSheetFile extends StyleSheetBase {
@@ -1788,6 +1797,7 @@ declare module 'svelte/compiler' {
 		export interface PseudoElementSelector extends BaseNode {
 			type: 'PseudoElementSelector';
 			name: string;
+			args?: SelectorList;
 		}
 
 		export interface PseudoClassSelector extends BaseNode {