optimise <title> - fixes #1027

src/generators/Generator.ts

@@ -738,6 +738,9 @@ export default class Generator {
 				} else if (node.name === ':Head') { // TODO do this in parse?
 					node.type = 'Head';
 					node.__proto__ = nodes.Head.prototype;
+				} else if (node.type === 'Element' && node.name === 'title') { // TODO do this in parse?
+					node.type = 'Title';
+					node.__proto__ = nodes.Title.prototype;
 				} else if (node.type === 'Element' && node.name === 'slot' && !generator.customElement) {
 					node.type = 'Slot';
 					node.__proto__ = nodes.Slot.prototype;

src/generators/nodes/Title.ts

@@ -0,0 +1,98 @@
+import { stringify } from '../../utils/stringify';
+import getExpressionPrecedence from '../../utils/getExpressionPrecedence';
+import Node from './shared/Node';
+import Block from '../dom/Block';
+
+export default class Title extends Node {
+	build(
+		block: Block,
+		parentNode: string,
+		parentNodes: string
+	) {
+		const isDynamic = !!this.children.find(node => node.type !== 'Text');
+
+		if (isDynamic) {
+			let value;
+
+			const allDependencies = new Set();
+			let shouldCache;
+
+			// TODO some of this code is repeated in Tag.ts — would be good to
+			// DRY it out if that's possible without introducing crazy indirection
+			if (this.children.length === 1) {
+				// single {{tag}} — may be a non-string
+				const { expression } = this.children[0];
+				const { indexes } = block.contextualise(expression);
+				const { dependencies, snippet } = this.children[0].metadata;
+
+				value = snippet;
+				dependencies.forEach(d => {
+					allDependencies.add(d);
+				});
+
+				shouldCache = (
+					expression.type !== 'Identifier' ||
+					block.contexts.has(expression.name)
+				);
+			} else {
+				// '{{foo}} {{bar}}' — treat as string concatenation
+				value =
+					(this.children[0].type === 'Text' ? '' : `"" + `) +
+					this.children
+						.map((chunk: Node) => {
+							if (chunk.type === 'Text') {
+								return stringify(chunk.data);
+							} else {
+								const { indexes } = block.contextualise(chunk.expression);
+								const { dependencies, snippet } = chunk.metadata;
+
+								dependencies.forEach(d => {
+									allDependencies.add(d);
+								});
+
+								return getExpressionPrecedence(chunk.expression) <= 13 ? `(${snippet})` : snippet;
+							}
+						})
+						.join(' + ');
+
+				shouldCache = true;
+			}
+
+			const last = shouldCache && block.getUniqueName(
+				`title_value`
+			);
+
+			if (shouldCache) block.addVariable(last);
+
+			let updater;
+			const init = shouldCache ? `${last} = ${value}` : value;
+
+			block.builders.init.addLine(
+				`document.title = ${init};`
+			);
+			updater = `document.title = ${shouldCache ? last : value};`;
+
+			if (allDependencies.size) {
+				const dependencies = Array.from(allDependencies);
+				const changedCheck = (
+					( block.hasOutroMethod ? `#outroing || ` : '' ) +
+					dependencies.map(dependency => `changed.${dependency}`).join(' || ')
+				);
+
+				const updateCachedValue = `${last} !== (${last} = ${value})`;
+
+				const condition = shouldCache ?
+					( dependencies.length ? `(${changedCheck}) && ${updateCachedValue}` : updateCachedValue ) :
+					changedCheck;
+
+				block.builders.update.addConditional(
+					condition,
+					updater
+				);
+			}
+		} else {
+			const value = stringify(this.children[0].data);
+			block.builders.hydrate.addLine(`document.title = ${value};`);
+		}
+	}
+}

src/generators/nodes/index.ts

@@ -19,6 +19,7 @@ import Ref from './Ref';
 import Slot from './Slot';
 import Text from './Text';
 import ThenBlock from './ThenBlock';
+import Title from './Title';
 import Transition from './Transition';
 import Window from './Window';
 
@@ -43,6 +44,7 @@ const nodes: Record<string, any> = {
 	Slot,
 	Text,
 	ThenBlock,
+	Title,
 	Transition,
 	Window
 };

src/generators/server-side-rendering/visitors/Title.ts

@@ -0,0 +1,19 @@
+import { SsrGenerator } from '../index';
+import Block from '../Block';
+import { escape } from '../../../utils/stringify';
+import visit from '../visit';
+import { Node } from '../../../interfaces';
+
+export default function visitTitle(
+	generator: SsrGenerator,
+	block: Block,
+	node: Node
+) {
+	generator.append(`<title>`);
+
+	node.children.forEach((child: Node) => {
+		visit(generator, block, child);
+	});
+
+	generator.append(`</title>`);
+}

src/generators/server-side-rendering/visitors/index.ts

@@ -9,6 +9,7 @@ import MustacheTag from './MustacheTag';
 import RawMustacheTag from './RawMustacheTag';
 import Slot from './Slot';
 import Text from './Text';
+import Title from './Title';
 import Window from './Window';
 
 export default {
@@ -23,5 +24,6 @@ export default {
 	RawMustacheTag,
 	Slot,
 	Text,
+	Title,
 	Window
 };

src/validate/html/validateElement.ts

@@ -3,7 +3,7 @@ import validateEventHandler from './validateEventHandler';
 import validate, { Validator } from '../index';
 import { Node } from '../../interfaces';
 
-const svg = /^(?:altGlyph|altGlyphDef|altGlyphItem|animate|animateColor|animateMotion|animateTransform|circle|clipPath|color-profile|cursor|defs|desc|discard|ellipse|feBlend|feColorMatrix|feComponentTransfer|feComposite|feConvolveMatrix|feDiffuseLighting|feDisplacementMap|feDistantLight|feDropShadow|feFlood|feFuncA|feFuncB|feFuncG|feFuncR|feGaussianBlur|feImage|feMerge|feMergeNode|feMorphology|feOffset|fePointLight|feSpecularLighting|feSpotLight|feTile|feTurbulence|filter|font|font-face|font-face-format|font-face-name|font-face-src|font-face-uri|foreignObject|g|glyph|glyphRef|hatch|hatchpath|hkern|image|line|linearGradient|marker|mask|mesh|meshgradient|meshpatch|meshrow|metadata|missing-glyph|mpath|path|pattern|polygon|polyline|radialGradient|rect|set|solidcolor|stop|switch|symbol|text|textPath|title|tref|tspan|unknown|use|view|vkern)$/;
+const svg = /^(?:altGlyph|altGlyphDef|altGlyphItem|animate|animateColor|animateMotion|animateTransform|circle|clipPath|color-profile|cursor|defs|desc|discard|ellipse|feBlend|feColorMatrix|feComponentTransfer|feComposite|feConvolveMatrix|feDiffuseLighting|feDisplacementMap|feDistantLight|feDropShadow|feFlood|feFuncA|feFuncB|feFuncG|feFuncR|feGaussianBlur|feImage|feMerge|feMergeNode|feMorphology|feOffset|fePointLight|feSpecularLighting|feSpotLight|feTile|feTurbulence|filter|font|font-face|font-face-format|font-face-name|font-face-src|font-face-uri|foreignObject|g|glyph|glyphRef|hatch|hatchpath|hkern|image|line|linearGradient|marker|mask|mesh|meshgradient|meshpatch|meshrow|metadata|missing-glyph|mpath|path|pattern|polygon|polyline|radialGradient|rect|set|solidcolor|stop|switch|symbol|text|textPath|tref|tspan|unknown|use|view|vkern)$/;
 
 export default function validateElement(
 	validator: Validator,
@@ -57,6 +57,24 @@ export default function validateElement(
 		}
 	}
 
+	if (node.name === 'title') {
+		if (node.attributes.length > 0) {
+			validator.error(
+				`<title> cannot have attributes`,
+				node.attributes[0].start
+			);
+		}
+
+		node.children.forEach(child => {
+			if (child.type !== 'Text' && child.type !== 'MustacheTag') {
+				validator.error(
+					`<title> can only contain text and {{tags}}`,
+					child.start
+				);
+			}
+		});
+	}
+
 	let hasIntro: boolean;
 	let hasOutro: boolean;
 	let hasTransition: boolean;

src/validate/html/validateHead.ts

@@ -1,3 +1,4 @@
+import validateElement from './validateElement';
 import { Validator } from '../index';
 import { Node } from '../../interfaces';
 
@@ -5,4 +6,11 @@ export default function validateHead(validator: Validator, node: Node, refs: Map
 	if (node.attributes.length) {
 		validator.error(`<:Head> should not have any attributes or directives`, node.start);
 	}
+
+	// TODO ensure only valid elements are included here
+
+	node.children.forEach(node => {
+		if (node.type !== 'Element') return; // TODO handle {{#if}} and friends?
+		validateElement(validator, node, refs, refCallees, [], []);
+	});
 }

test/js/samples/title/expected-bundle.js

@@ -0,0 +1,208 @@
+function noop() {}
+
+function assign(target) {
+	var k,
+		source,
+		i = 1,
+		len = arguments.length;
+	for (; i < len; i++) {
+		source = arguments[i];
+		for (k in source) target[k] = source[k];
+	}
+
+	return target;
+}
+
+function blankObject() {
+	return Object.create(null);
+}
+
+function destroy(detach) {
+	this.destroy = noop;
+	this.fire('destroy');
+	this.set = this.get = noop;
+
+	if (detach !== false) this._fragment.u();
+	this._fragment.d();
+	this._fragment = this._state = null;
+}
+
+function differs(a, b) {
+	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+}
+
+function dispatchObservers(component, group, changed, newState, oldState) {
+	for (var key in group) {
+		if (!changed[key]) continue;
+
+		var newValue = newState[key];
+		var oldValue = oldState[key];
+
+		var callbacks = group[key];
+		if (!callbacks) continue;
+
+		for (var i = 0; i < callbacks.length; i += 1) {
+			var callback = callbacks[i];
+			if (callback.__calling) continue;
+
+			callback.__calling = true;
+			callback.call(component, newValue, oldValue);
+			callback.__calling = false;
+		}
+	}
+}
+
+function fire(eventName, data) {
+	var handlers =
+		eventName in this._handlers && this._handlers[eventName].slice();
+	if (!handlers) return;
+
+	for (var i = 0; i < handlers.length; i += 1) {
+		handlers[i].call(this, data);
+	}
+}
+
+function get(key) {
+	return key ? this._state[key] : this._state;
+}
+
+function init(component, options) {
+	component._observers = { pre: blankObject(), post: blankObject() };
+	component._handlers = blankObject();
+	component._bind = options._bind;
+
+	component.options = options;
+	component.root = options.root || component;
+	component.store = component.root.store || options.store;
+}
+
+function observe(key, callback, options) {
+	var group = options && options.defer
+		? this._observers.post
+		: this._observers.pre;
+
+	(group[key] || (group[key] = [])).push(callback);
+
+	if (!options || options.init !== false) {
+		callback.__calling = true;
+		callback.call(this, this._state[key]);
+		callback.__calling = false;
+	}
+
+	return {
+		cancel: function() {
+			var index = group[key].indexOf(callback);
+			if (~index) group[key].splice(index, 1);
+		}
+	};
+}
+
+function on(eventName, handler) {
+	if (eventName === 'teardown') return this.on('destroy', handler);
+
+	var handlers = this._handlers[eventName] || (this._handlers[eventName] = []);
+	handlers.push(handler);
+
+	return {
+		cancel: function() {
+			var index = handlers.indexOf(handler);
+			if (~index) handlers.splice(index, 1);
+		}
+	};
+}
+
+function set(newState) {
+	this._set(assign({}, newState));
+	if (this.root._lock) return;
+	this.root._lock = true;
+	callAll(this.root._beforecreate);
+	callAll(this.root._oncreate);
+	callAll(this.root._aftercreate);
+	this.root._lock = false;
+}
+
+function _set(newState) {
+	var oldState = this._state,
+		changed = {},
+		dirty = false;
+
+	for (var key in newState) {
+		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+	}
+	if (!dirty) return;
+
+	this._state = assign({}, oldState, newState);
+	this._recompute(changed, this._state);
+	if (this._bind) this._bind(changed, this._state);
+
+	if (this._fragment) {
+		dispatchObservers(this, this._observers.pre, changed, this._state, oldState);
+		this._fragment.p(changed, this._state);
+		dispatchObservers(this, this._observers.post, changed, this._state, oldState);
+	}
+}
+
+function callAll(fns) {
+	while (fns && fns.length) fns.pop()();
+}
+
+function _mount(target, anchor) {
+	this._fragment.m(target, anchor);
+}
+
+function _unmount() {
+	if (this._fragment) this._fragment.u();
+}
+
+var proto = {
+	destroy: destroy,
+	get: get,
+	fire: fire,
+	observe: observe,
+	on: on,
+	set: set,
+	teardown: destroy,
+	_recompute: noop,
+	_set: _set,
+	_mount: _mount,
+	_unmount: _unmount
+};
+
+/* generated by Svelte vX.Y.Z */
+function create_main_fragment(state, component) {
+	var title_value;
+
+	document.title = title_value = "a " + state.custom + " title";
+
+	return {
+		c: noop,
+
+		m: noop,
+
+		p: function update(changed, state) {
+			if ((changed.custom) && title_value !== (title_value = "a " + state.custom + " title")) {
+				document.title = title_value;
+			}
+		},
+
+		u: noop,
+
+		d: noop
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	this._state = assign({}, options.data);
+
+	this._fragment = create_main_fragment(this._state, this);
+
+	if (options.target) {
+		this._fragment.c();
+		this._fragment.m(options.target, options.anchor || null);
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+
+export default SvelteComponent;

test/js/samples/title/expected.js

@@ -0,0 +1,39 @@
+/* generated by Svelte vX.Y.Z */
+import { assign, init, noop, proto } from "svelte/shared.js";
+
+function create_main_fragment(state, component) {
+	var title_value;
+
+	document.title = title_value = "a " + state.custom + " title";
+
+	return {
+		c: noop,
+
+		m: noop,
+
+		p: function update(changed, state) {
+			if ((changed.custom) && title_value !== (title_value = "a " + state.custom + " title")) {
+				document.title = title_value;
+			}
+		},
+
+		u: noop,
+
+		d: noop
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	this._state = assign({}, options.data);
+
+	this._fragment = create_main_fragment(this._state, this);
+
+	if (options.target) {
+		this._fragment.c();
+		this._fragment.m(options.target, options.anchor || null);
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+export default SvelteComponent;

test/js/samples/title/input.html

@@ -0,0 +1,3 @@
+<:Head>
+	<title>a {{custom}} title</title>
+</:Head>

test/runtime/index.js

@@ -59,6 +59,7 @@ describe("runtime", () => {
 			}
 
 			const cwd = path.resolve(`test/runtime/samples/${dir}`);
+			global.document.title = '';
 
 			compileOptions = config.compileOptions || {};
 			compileOptions.shared = shared;

test/validator/samples/title-no-attributes/errors.json

@@ -0,0 +1,8 @@
+[{
+	"message": "<title> cannot have attributes",
+	"loc": {
+		"line": 2,
+		"column": 8
+	},
+	"pos": 16
+}]

test/validator/samples/title-no-attributes/input.html

@@ -0,0 +1,3 @@
+<:Head>
+	<title data-invalid=true>a static title</title>
+</:Head>

test/validator/samples/title-no-children/errors.json

@@ -0,0 +1,8 @@
+[{
+	"message": "<title> can only contain text and {{tags}}",
+	"loc": {
+		"line": 2,
+		"column": 11
+	},
+	"pos": 19
+}]

test/validator/samples/title-no-children/input.html

@@ -0,0 +1,3 @@
+<:Head>
+	<title>an <strong>invalid</strong> title</title>
+</:Head>