feat: implement `:global {...}` CSS blocks

.changeset/small-apples-eat.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+feat: implement `:global {...}` CSS blocks

packages/svelte/src/compiler/errors.js

@@ -103,6 +103,14 @@ const css = {
 	/** @param {string} message */
 	'css-parse-error': (message) => message,
 	'invalid-css-empty-declaration': () => `Declaration cannot be empty`,
+	'invalid-css-global-block-list': () =>
+		`A :global {...} block cannot be part of a selector list with more than one item`,
+	'invalid-css-global-block-modifier': () =>
+		`A :global {...} block cannot modify an existing selector`,
+	'invalid-css-global-block-combinator': (name) =>
+		`A :global {...} block cannot follow a ${name} combinator`,
+	'invalid-css-global-block-declaration': () =>
+		`A :global {...} block can only contain rules, not declarations`,
 	'invalid-css-global-placement': () =>
 		`:global(...) can be at the start or end of a selector sequence, but not in the middle`,
 	'invalid-css-global-selector': () => `:global(...) must contain exactly one selector`,

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

@@ -3,7 +3,6 @@ import { error } from '../../../errors.js';
 const REGEX_MATCHER = /^[~^$*|]?=/;
 const REGEX_CLOSING_BRACKET = /[\s\]]/;
 const REGEX_ATTRIBUTE_FLAGS = /^[a-zA-Z]+/; // only `i` and `s` are valid today, but make it future-proof
-const REGEX_COMBINATOR_WHITESPACE = /^\s*(\+|~|>|\|\|)\s*/;
 const REGEX_COMBINATOR = /^(\+|~|>|\|\|)/;
 const REGEX_PERCENTAGE = /^\d+(\.\d+)?%/;
 const REGEX_NTH_OF =
@@ -116,7 +115,8 @@ function read_rule(parser) {
 		end: parser.index,
 		metadata: {
 			parent_rule: null,
-			has_local_selectors: false
+			has_local_selectors: false,
+			is_global_block: false
 		}
 	};
 }
@@ -252,8 +252,6 @@ function read_selector(parser, inside_pseudo_class = false) {
 			if (parser.eat('(')) {
 				args = read_selector_list(parser, true);
 				parser.eat(')', true);
-			} else if (name === 'global') {
-				error(parser.index, 'invalid-css-global-selector');
 			}
 
 			relative_selector.selectors.push({

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

@@ -69,6 +69,17 @@ const analysis_visitors = {
 	Rule(node, context) {
 		node.metadata.parent_rule = context.state.rule;
 
+		// `:global {...}` or `div :global {...}`
+		node.metadata.is_global_block = node.prelude.children.some((selector) => {
+			const last = selector.children[selector.children.length - 1];
+
+			const s = last.selectors[last.selectors.length - 1];
+
+			if (s.type === 'PseudoClassSelector' && s.name === 'global' && s.args === null) {
+				return true;
+			}
+		});
+
 		context.next({
 			...context.state,
 			rule: node
@@ -84,6 +95,39 @@ const analysis_visitors = {
 
 /** @type {Visitors} */
 const validation_visitors = {
+	Rule(node, context) {
+		if (node.metadata.is_global_block) {
+			if (node.prelude.children.length > 1) {
+				error(node.prelude, 'invalid-css-global-block-list');
+			}
+
+			const complex_selector = node.prelude.children[0];
+			const relative_selector = complex_selector.children[complex_selector.children.length - 1];
+
+			if (relative_selector.selectors.length > 1) {
+				error(
+					relative_selector.selectors[relative_selector.selectors.length - 1],
+					'invalid-css-global-block-modifier'
+				);
+			}
+
+			if (relative_selector.combinator && relative_selector.combinator.name !== ' ') {
+				error(
+					relative_selector,
+					'invalid-css-global-block-combinator',
+					relative_selector.combinator.name
+				);
+			}
+
+			const declaration = node.block.children.find((child) => child.type === 'Declaration');
+
+			if (declaration) {
+				error(declaration, 'invalid-css-global-block-declaration');
+			}
+		}
+
+		context.next();
+	},
 	ComplexSelector(node, context) {
 		// ensure `:global(...)` is not used in the middle of a selector
 		{

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

@@ -1,7 +1,6 @@
 import { walk } from 'zimmerframe';
 import { get_possible_values } from './utils.js';
 import { regex_ends_with_whitespace, regex_starts_with_whitespace } from '../../patterns.js';
-import { error } from '../../../errors.js';
 
 /**
  * @typedef {{
@@ -60,6 +59,13 @@ export function prune(stylesheet, element) {
 
 /** @type {import('zimmerframe').Visitors<import('#compiler').Css.Node, State>} */
 const visitors = {
+	Rule(node, context) {
+		if (node.metadata.is_global_block) {
+			context.visit(node.prelude);
+		} else {
+			context.next();
+		}
+	},
 	ComplexSelector(node, context) {
 		const selectors = truncate(node);
 		const inner = selectors[selectors.length - 1];

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

@@ -30,5 +30,12 @@ const visitors = {
 		}
 
 		context.next();
+	},
+	Rule(node, context) {
+		if (node.metadata.is_global_block) {
+			context.visit(node.prelude);
+		} else {
+			context.next();
+		}
 	}
 };

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

@@ -116,7 +116,7 @@ const visitors = {
 			}
 		}
 	},
-	Rule(node, { state, next }) {
+	Rule(node, { state, next, visit }) {
 		// keep empty rules in dev, because it's convenient to
 		// see them in devtools
 		if (!state.dev && is_empty(node)) {
@@ -134,6 +134,26 @@ const visitors = {
 			return;
 		}
 
+		if (node.metadata.is_global_block) {
+			const selector = node.prelude.children[0];
+
+			if (selector.children.length === 1) {
+				// `:global {...}`
+				state.code.prependRight(node.start, '/* ');
+				state.code.appendLeft(node.block.start + 1, '*/');
+
+				state.code.prependRight(node.block.end - 1, '/*');
+				state.code.appendLeft(node.block.end, '*/');
+
+				// don't recurse into selector or body
+				return;
+			}
+
+			// don't recurse into body
+			visit(node.prelude);
+			return;
+		}
+
 		next();
 	},
 	SelectorList(node, { state, next, path }) {
@@ -275,6 +295,10 @@ const visitors = {
 
 /** @param {import('#compiler').Css.Rule} rule */
 function is_empty(rule) {
+	if (rule.metadata.is_global_block) {
+		return rule.block.children.length === 0;
+	}
+
 	for (const child of rule.block.children) {
 		if (child.type === 'Declaration') {
 			return false;

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

@@ -33,6 +33,7 @@ export namespace Css {
 		metadata: {
 			parent_rule: null | Rule;
 			has_local_selectors: boolean;
+			is_global_block: boolean;
 		};
 	}
 

packages/svelte/tests/css/samples/global-block/_config.js

@@ -0,0 +1,21 @@
+import { test } from '../../test';
+
+export default test({
+	warnings: [
+		{
+			filename: 'SvelteComponent.svelte',
+			code: 'css-unused-selector',
+			message: 'Unused CSS selector ".unused :global"',
+			start: {
+				line: 16,
+				column: 1,
+				character: 128
+			},
+			end: {
+				line: 16,
+				column: 16,
+				character: 143
+			}
+		}
+	]
+});

packages/svelte/tests/css/samples/global-block/expected.css

@@ -0,0 +1,17 @@
+	/* :global {*/
+		.x {
+			color: green;
+		}
+	/*}*/
+
+	div.svelte-xyz {
+		.y {
+			color: green;
+		}
+	}
+
+	/* (unused) .unused :global {
+		.z {
+			color: red;
+		}
+	}*/

packages/svelte/tests/css/samples/global-block/input.svelte

@@ -0,0 +1,21 @@
+<div>{@html whatever}</div>
+
+<style>
+	:global {
+		.x {
+			color: green;
+		}
+	}
+
+	div :global {
+		.y {
+			color: green;
+		}
+	}
+
+	.unused :global {
+		.z {
+			color: red;
+		}
+	}
+</style>