Warn on unused selectors

src/generators/Generator.ts

@@ -1,5 +1,7 @@
 import MagicString, { Bundle } from 'magic-string';
 import { walk } from 'estree-walker';
+import { getLocator } from 'locate-character';
+import getCodeFrame from '../utils/getCodeFrame';
 import isReference from '../utils/isReference';
 import flattenReference from '../utils/flattenReference';
 import globalWhitelist from '../utils/globalWhitelist';
@@ -13,6 +15,8 @@ import annotateWithScopes from '../utils/annotateWithScopes';
 import clone from '../utils/clone';
 import DomBlock from './dom/Block';
 import SsrBlock from './server-side-rendering/Block';
+import { walkRules } from '../utils/css';
+import Selector from './Selector';
 import { Node, Parsed, CompileOptions } from '../interfaces';
 
 const test = typeof global !== 'undefined' && global.__svelte_test;
@@ -40,6 +44,8 @@ export default class Generator {
 	cssId: string;
 	usesRefs: boolean;
 
+	selectors: Selector[];
+
 	importedNames: Set<string>;
 	aliases: Map<string, string>;
 	usedNames: Set<string>;
@@ -71,10 +77,21 @@ export default class Generator {
 		this.expectedProperties = new Set();
 
 		this.code = new MagicString(source);
+		this.usesRefs = false;
+
+		// styles
 		this.cascade = options.cascade !== false; // TODO remove this option in v2
 		this.css = parsed.css ? processCss(parsed, this.code, this.cascade) : null;
 		this.cssId = parsed.css ? `svelte-${parsed.hash}` : '';
-		this.usesRefs = false;
+		this.selectors = [];
+
+		if (parsed.css) {
+			walkRules(parsed.css.children, node => {
+				node.selector.children.forEach((child: Node) => {
+					this.selectors.push(new Selector(child));
+				});
+			});
+		}
 
 		// allow compiler to deconflict user's `import { get } from 'whatever'` and
 		// Svelte's builtin `import { get, ... } from 'svelte/shared.ts'`;
@@ -211,6 +228,20 @@ export default class Generator {
 		};
 	}
 
+	applyCss(node: Node, stack: Node[]) {
+		if (!this.cssId) return;
+
+		if (this.cascade) {
+			if (stack.length === 0) node._needsCssAttribute = true;
+			return;
+		}
+
+		for (let i = 0; i < this.selectors.length; i += 1) {
+			const selector = this.selectors[i];
+			selector.apply(node, stack);
+		}
+	}
+
 	findDependencies(
 		contextDependencies: Map<string, string[]>,
 		indexes: Map<string, string>,
@@ -590,4 +621,31 @@ export default class Generator {
 		this.namespace = namespace;
 		this.templateProperties = templateProperties;
 	}
+
+	warnOnUnusedSelectors() {
+		if (this.cascade) return;
+
+		let locator;
+
+		this.selectors.forEach((selector: Selector) => {
+			if (!selector.used) {
+				const pos = selector.node.start;
+
+				if (!locator) locator = getLocator(this.source);
+				const { line, column } = locator(pos);
+
+				const frame = getCodeFrame(this.source, line, column);
+				const message = `Unused CSS selector`;
+
+				this.options.onwarn({
+					message,
+					frame,
+					loc: { line: line + 1, column },
+					pos,
+					filename: this.options.filename,
+					toString: () => `${message} (${line + 1}:${column})\n${frame}`,
+				});
+			}
+		});
+	}
 }

src/generators/Selector.ts

@@ -0,0 +1,150 @@
+import { groupSelectors, isGlobalSelector, walkRules } from '../utils/css';
+import { Node } from '../interfaces';
+
+export default class Selector {
+	node: Node;
+	blocks: Node[][];
+	parts: Node[];
+	used: boolean;
+
+	constructor(node: Node) {
+		this.node = node;
+
+		this.blocks = groupSelectors(this.node);
+
+		// take trailing :global(...) selectors out of consideration
+		let i = node.children.length;
+		while (i > 2) {
+			const last = node.children[i-1];
+			const penultimate = node.children[i-2];
+
+			if (last.type === 'PseudoClassSelector' && last.name === 'global') {
+				i -= 2;
+			} else {
+				break;
+			}
+		}
+
+		this.parts = node.children.slice(0, i);
+
+		this.used = isGlobalSelector(this.blocks[0]);
+	}
+
+	apply(node: Node, stack: Node[]) {
+		const applies = selectorAppliesTo(this.parts, node, stack.slice());
+
+		if (applies) {
+			this.used = true;
+
+			// add svelte-123xyz attribute to outermost and innermost
+			// elements — no need to add it to intermediate elements
+			node._needsCssAttribute = true;
+			if (stack[0] && this.node.children.find(isDescendantSelector)) stack[0]._needsCssAttribute = true;
+		}
+	}
+}
+
+function isDescendantSelector(selector: Node) {
+	return selector.type === 'WhiteSpace' || selector.type === 'Combinator';
+}
+
+function selectorAppliesTo(parts: Node[], node: Node, stack: Node[]): boolean {
+	let i = parts.length;
+	let j = stack.length;
+
+	while (i--) {
+		if (!node) {
+			return parts.every((part: Node) => {
+				return part.type === 'Combinator' || (part.type === 'PseudoClassSelector' && part.name === 'global');
+			});
+		}
+
+		const part = parts[i];
+
+		if (part.type === 'PseudoClassSelector' && part.name === 'global') {
+			// TODO shouldn't see this here... maybe we should enforce that :global(...)
+			// cannot be sandwiched between non-global selectors?
+			return false;
+		}
+
+		if (part.type === 'PseudoClassSelector' || part.type === 'PseudoElementSelector') {
+			continue;
+		}
+
+		if (part.type === 'ClassSelector') {
+			if (!attributeMatches(node, 'class', part.name, '~=', false)) return false;
+		}
+
+		else if (part.type === 'IdSelector') {
+			if (!attributeMatches(node, 'id', part.name, '=', false)) return false;
+		}
+
+		else if (part.type === 'AttributeSelector') {
+			if (!attributeMatches(node, part.name.name, part.value && unquote(part.value.value), part.operator, part.flags)) return false;
+		}
+
+		else if (part.type === 'TypeSelector') {
+			if (part.name === '*') return true;
+			if (node.name !== part.name) return false;
+		}
+
+		else if (part.type === 'WhiteSpace') {
+			parts = parts.slice(0, i);
+
+			while (stack.length) {
+				if (selectorAppliesTo(parts, stack.pop(), stack)) {
+					return true;
+				}
+			}
+
+			return false;
+		}
+
+		else if (part.type === 'Combinator') {
+			if (part.name === '>') {
+				return selectorAppliesTo(parts.slice(0, i), stack.pop(), stack);
+			}
+
+			// TODO other combinators
+			return true;
+		}
+
+		else {
+			// bail. TODO figure out what these could be
+			return true;
+		}
+	}
+
+	return true;
+}
+
+const operators = {
+	'=' : (value: string, flags: string) => new RegExp(`^${value}$`, flags),
+	'~=': (value: string, flags: string) => new RegExp(`\\b${value}\\b`, flags),
+	'|=': (value: string, flags: string) => new RegExp(`^${value}(-.+)?$`, flags),
+	'^=': (value: string, flags: string) => new RegExp(`^${value}`, flags),
+	'$=': (value: string, flags: string) => new RegExp(`${value}$`, flags),
+	'*=': (value: string, flags: string) => new RegExp(value, flags)
+};
+
+function attributeMatches(node: Node, name: string, expectedValue: string, operator: string, caseInsensitive: boolean) {
+	const attr = node.attributes.find((attr: Node) => attr.name === name);
+	if (!attr) return false;
+	if (attr.value === true) return operator === null;
+	if (isDynamic(attr.value)) return true;
+
+	const actualValue = attr.value[0].data;
+
+	const pattern = operators[operator](expectedValue, caseInsensitive ? 'i' : '');
+	return pattern.test(actualValue);
+}
+
+function isDynamic(value: Node) {
+	return value.length > 1 || value[0].type !== 'Text';
+}
+
+function unquote(str: string) {
+	if (str[0] === str[str.length - 1] && str[0] === "'" || str[0] === '"') {
+		return str.slice(1, str.length - 1);
+	}
+}

src/generators/dom/index.ts

@@ -61,8 +61,10 @@ export default function dom(
 
 	const { block, state } = preprocess(generator, namespace, parsed.html);
 
+	generator.warnOnUnusedSelectors();
+
 	parsed.html.children.forEach((node: Node) => {
-		visit(generator, block, state, node);
+		visit(generator, block, state, node, []);
 	});
 
 	const builder = new CodeBuilder();