class:"..." for single class: on the client

#7170 / #12610 / #7294

todos:
- language-tools support (syntax highlighting & intellisense)
- playground syntax highlighting?
- ssr

packages/svelte/src/compiler/phases/1-parse/state/element.js

@@ -496,7 +496,7 @@ function read_attribute(parser) {
 		}
 	}
 
-	const name = parser.read_until(regex_token_ending_character);
+	let name = parser.read_until(regex_token_ending_character);
 	if (!name) return null;
 
 	let end = parser.index;
@@ -512,15 +512,32 @@ function read_attribute(parser) {
 		parser.allow_whitespace();
 		value = read_attribute_value(parser);
 		end = parser.index;
-	} else if (parser.match_regex(regex_starts_with_quote_characters)) {
+	} else if (parser.match_regex(regex_starts_with_quote_characters) && type !== 'ClassDirective') {
 		e.expected_token(parser.index, '=');
 	}
 
 	if (type) {
 		const [directive_name, ...modifiers] = name.slice(colon_index + 1).split('|');
+		/** @type {Array<AST.Text | AST.ExpressionTag> | null} */
+		let class_name_value = null;
 
 		if (directive_name === '') {
+			if (type !== 'ClassDirective') {
 				e.directive_missing_name({ start, end: start + colon_index + 1 }, name);
+			} else {
+				// class:"..." case
+				const v = read_attribute_value(parser);
+				if (!Array.isArray(v)) e.expected_token(v.start, '" or =');
+				class_name_value = v;
+
+				if (parser.eat('=')) {
+					parser.allow_whitespace();
+					value = read_attribute_value(parser);
+					end = parser.index;
+				} else if (parser.match_regex(regex_starts_with_quote_characters)) {
+					e.expected_token(parser.index, '=');
+				}
+			}
 		}
 
 		if (type === 'StyleDirective') {
@@ -569,6 +586,10 @@ function read_attribute(parser) {
 			}
 		};
 
+		if (directive.type === 'ClassDirective') {
+			directive.value = class_name_value;
+		}
+
 		if (directive.type === 'TransitionDirective') {
 			const direction = name.slice(0, colon_index);
 			directive.intro = direction === 'in' || direction === 'transition';

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

@@ -627,7 +627,13 @@ function relative_selector_might_apply_to_node(relative_selector, rule, element,
 				if (
 					!attribute_matches(element, 'class', name, '~=', false) &&
 					!element.attributes.some(
-						(attribute) => attribute.type === 'ClassDirective' && attribute.name === name
+						(attribute) =>
+							attribute.type === 'ClassDirective' &&
+							(attribute.name === name ||
+								(attribute.value &&
+									(attribute.value.length > 1 ||
+										attribute.value[0].type !== 'Text' ||
+										test_attribute('~=', name, false, attribute.value[0].data))))
 					)
 				) {
 					return false;

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/element.js

@@ -1,9 +1,9 @@
-/** @import { Expression, Identifier, ObjectExpression } from 'estree' */
+/** @import { Expression, ExpressionStatement, Identifier, ObjectExpression } from 'estree' */
-/** @import { AST, Namespace } from '#compiler' */
+/** @import { AST } from '#compiler' */
 /** @import { ComponentClientTransformState, ComponentContext } from '../../types' */
 import { normalize_attribute } from '../../../../../../utils.js';
 import { is_ignored } from '../../../../../state.js';
-import { get_attribute_expression, is_event_attribute } from '../../../../../utils/ast.js';
+import { is_event_attribute } from '../../../../../utils/ast.js';
 import * as b from '../../../../../utils/builders.js';
 import { build_getter, create_derived } from '../../utils.js';
 import { build_template_literal, build_update } from './utils.js';
@@ -154,7 +154,7 @@ export function build_class_directives(
 ) {
 	const state = context.state;
 	for (const directive of class_directives) {
-		const { has_state, has_call } = directive.metadata.expression;
+		let { has_state, has_call } = directive.metadata.expression;
 		let value = /** @type {Expression} */ (context.visit(directive.expression));
 
 		if (has_call) {
@@ -164,7 +164,37 @@ export function build_class_directives(
 			value = b.call('$.get', id);
 		}
 
-		const update = b.stmt(b.call('$.toggle_class', element_id, b.literal(directive.name), value));
+		/** @type {ExpressionStatement} */
+		let update;
+
+		if (!directive.value) {
+			update = b.stmt(b.call('$.toggle_class', element_id, b.literal(directive.name), value));
+		} else {
+			let prev_id;
+			let {
+				has_call: h_c,
+				has_state: h_s,
+				value: name
+			} = build_attribute_value(directive.value, context);
+
+			has_call ||= h_c;
+			has_state ||= h_s;
+
+			if (h_c || h_s) {
+				prev_id = b.id(state.scope.generate('prev_class_names'));
+				state.init.push(b.let(prev_id, b.literal('')));
+			}
+
+			if (has_call) {
+				const id = b.id(state.scope.generate('class_directive'));
+
+				state.init.push(b.const(id, create_derived(state, b.thunk(name))));
+				name = b.call('$.get', id);
+			}
+
+			const toggle = b.call('$.toggle_classes', element_id, name, value, prev_id);
+			update = b.stmt(prev_id ? b.assignment('=', prev_id, toggle) : toggle);
+		}
 
 		if (!is_attributes_reactive && has_call) {
 			state.init.push(build_update(update));

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

@@ -196,8 +196,10 @@ export namespace AST {
 	/** A `class:` directive */
 	export interface ClassDirective extends BaseNode {
 		type: 'ClassDirective';
-		/** The 'x' in `class:x` */
+		/** The 'x' in `class:x`, empty string in case of `class:"..."` */
-		name: 'class';
+		name: string;
+		/** The 'x' in `class:"x"`, `null` in case of `class:x` (i.e. when no quotes) */
+		value: Array<Text | ExpressionTag> | null;
 		/** The 'y' in `class:x={y}`, or the `x` in `class:x` */
 		expression: Expression;
 		/** @internal */

packages/svelte/src/internal/client/dom/elements/class.js

@@ -114,3 +114,21 @@ export function toggle_class(dom, class_name, value) {
 		dom.classList.remove(class_name);
 	}
 }
+
+/**
+ * @param {Element} dom
+ * @param {string} class_names
+ * @param {boolean} value
+ * @param {string} prev_class_names
+ * @returns {string}
+ */
+export function toggle_classes(dom, class_names, value, prev_class_names) {
+	const split_classes = class_names.split(' ');
+	split_classes.forEach((class_name) => toggle_class(dom, class_name, value));
+	prev_class_names.split(' ').forEach((class_name) => {
+		if (!split_classes.includes(class_name)) {
+			toggle_class(dom, class_name, false);
+		}
+	});
+	return class_names;
+}

packages/svelte/src/internal/client/index.js

@@ -35,7 +35,13 @@ export {
 	set_value,
 	set_checked
 } from './dom/elements/attributes.js';
-export { set_class, set_svg_class, set_mathml_class, toggle_class } from './dom/elements/class.js';
+export {
+	set_class,
+	set_svg_class,
+	set_mathml_class,
+	toggle_class,
+	toggle_classes
+} from './dom/elements/class.js';
 export { apply, event, delegate, replay_events } from './dom/elements/events.js';
 export { autofocus, remove_textarea_child } from './dom/elements/misc.js';
 export { set_style } from './dom/elements/style.js';