feat: improve hydration, claim static html elements using innerHTML instead of deopt to claiming every nodes (#7426)

Related: #7341, #7226

For purely static HTML, instead of walking the node tree and claiming every node/text etc, hydration now uses the same innerHTML optimization technique for hydration compared to normal create. It uses a new data-svelte-h attribute which is added upon server side rendering containing a hash (computed at build time), and then comparing that hash in the client to ensure it's the same node. If the hash is the same, the whole child content is expected to be the same. If the hash is different, the whole child content is replaced with innerHTML.

---------

Co-authored-by: Simon H <[email protected]>
Co-authored-by: Ben McCann <[email protected]>
Co-authored-by: Simon Holthausen <[email protected]>

Author: 3 people

src/compiler/compile/Component.ts

@@ -38,6 +38,7 @@ import compiler_warnings from './compiler_warnings';
 import compiler_errors from './compiler_errors';
 import { extract_ignores_above_position, extract_svelte_ignore_from_comments } from '../utils/extract_svelte_ignore';
 import check_enable_sourcemap from './utils/check_enable_sourcemap';
+import Tag from './nodes/shared/Tag';
 
 interface ComponentOptions {
 	namespace?: string;
@@ -110,6 +111,8 @@ export default class Component {
 	slots: Map<string, Slot> = new Map();
 	slot_outlets: Set<string> = new Set();
 
+	tags: Tag[] = [];
+
 	constructor(
 		ast: Ast,
 		source: string,
@@ -761,6 +764,7 @@ export default class Component {
 
 		this.hoist_instance_declarations();
 		this.extract_reactive_declarations();
+		this.check_if_tags_content_dynamic();
 	}
 
 	post_template_walk() {
@@ -1479,6 +1483,12 @@ export default class Component {
 		unsorted_reactive_declarations.forEach(add_declaration);
 	}
 
+	check_if_tags_content_dynamic() {
+		this.tags.forEach(tag => {
+			tag.check_if_content_dynamic();
+		});
+	}
+
 	warn_if_undefined(name: string, node, template_scope: TemplateScope) {
 		if (name[0] === '$') {
 			if (name === '$' || name[1] === '$' && !is_reserved_keyword(name)) {

src/compiler/compile/nodes/Attribute.ts

@@ -59,6 +59,11 @@ export default class Attribute extends Node {
 					return expression;
 				});
 		}
+
+		if (this.dependencies.size > 0) {
+			parent.cannot_use_innerhtml();
+			parent.not_static_content();
+		}
 	}
 
 	get_dependencies() {

src/compiler/compile/nodes/AwaitBlock.ts

@@ -27,6 +27,8 @@ export default class AwaitBlock extends Node {
 
 	constructor(component: Component, parent: Node, scope: TemplateScope, info: TemplateNode) {
 		super(component, parent, scope, info);
+		this.cannot_use_innerhtml();
+		this.not_static_content();
 
 		this.expression = new Expression(component, this, scope, info.expression);
 

src/compiler/compile/nodes/EachBlock.ts

@@ -33,6 +33,8 @@ export default class EachBlock extends AbstractBlock {
 
 	constructor(component: Component, parent: Node, scope: TemplateScope, info: TemplateNode) {
 		super(component, parent, scope, info);
+		this.cannot_use_innerhtml();
+		this.not_static_content();
 
 		this.expression = new Expression(component, this, scope, info.expression);
 		this.context = info.context.name || 'each'; // TODO this is used to facilitate binding; currently fails with destructuring

src/compiler/compile/nodes/Element.ts

@@ -15,6 +15,7 @@ import { is_name_contenteditable, get_contenteditable_attr, has_contenteditable_
 import { regex_dimensions, regex_starts_with_newline, regex_non_whitespace_character, regex_box_size } from '../../utils/patterns';
 import fuzzymatch from '../../utils/fuzzymatch';
 import list from '../../utils/list';
+import hash from '../utils/hash';
 import Let from './Let';
 import TemplateScope from './shared/TemplateScope';
 import { INode } from './interfaces';
@@ -503,6 +504,25 @@ export default class Element extends Node {
 		this.optimise();
 
 		component.apply_stylesheet(this);
+
+		if (this.parent) {
+			if (this.actions.length > 0 ||
+				this.animation ||
+				this.bindings.length > 0 ||
+				this.classes.length > 0 ||
+				this.intro || this.outro ||
+				this.handlers.length > 0 ||
+				this.styles.length > 0 ||
+				this.name === 'option' ||
+				this.is_dynamic_element ||
+				this.tag_expr.dynamic_dependencies().length ||
+				this.is_dynamic_element ||
+				component.compile_options.dev
+			) {
+				this.parent.cannot_use_innerhtml(); // need to use add_location
+				this.parent.not_static_content();
+			}
+		}
 	}
 
 	validate() {
@@ -1262,6 +1282,20 @@ export default class Element extends Node {
 			}
 		});
 	}
+
+	get can_use_textcontent() {
+		return this.is_static_content && this.children.every(node => node.type === 'Text' || node.type === 'MustacheTag');
+	}
+
+	get can_optimise_to_html_string() {
+		const can_use_textcontent = this.can_use_textcontent;
+		const is_template_with_text_content = this.name === 'template' && can_use_textcontent;
+		return !is_template_with_text_content && !this.namespace && (this.can_use_innerhtml || can_use_textcontent) && this.children.length > 0;
+	}
+
+	hash() {
+		return `svelte-${hash(this.component.source.slice(this.start, this.end))}`;
+	}
 }
 
 const regex_starts_with_vowel = /^[aeiou]/;

src/compiler/compile/nodes/Head.ts

@@ -15,6 +15,8 @@ export default class Head extends Node {
 	constructor(component: Component, parent: Node, scope: TemplateScope, info: TemplateNode) {
 		super(component, parent, scope, info);
 
+		this.cannot_use_innerhtml();
+
 		if (info.attributes.length) {
 			component.error(info.attributes[0], compiler_errors.invalid_attribute_head);
 			return;

src/compiler/compile/nodes/IfBlock.ts

@@ -18,6 +18,8 @@ export default class IfBlock extends AbstractBlock {
 	constructor(component: Component, parent: Node, scope: TemplateScope, info: TemplateNode) {
 		super(component, parent, scope, info);
 		this.scope = scope.child();
+		this.cannot_use_innerhtml();
+		this.not_static_content();
 
 		this.expression = new Expression(component, this, this.scope, info.expression);
 		([this.const_tags, this.children] = get_const_tags(info.children, component, this, this));

src/compiler/compile/nodes/InlineComponent.ts

@@ -28,6 +28,9 @@ export default class InlineComponent extends Node {
 	constructor(component: Component, parent: Node, scope: TemplateScope, info: TemplateNode) {
 		super(component, parent, scope, info);
 
+		this.cannot_use_innerhtml();
+		this.not_static_content();
+
 		if (info.name !== 'svelte:component' && info.name !== 'svelte:self') {
 			const name = info.name.split('.')[0]; // accommodate namespaces
 			component.warn_if_undefined(name, info, scope);

src/compiler/compile/nodes/KeyBlock.ts

@@ -13,6 +13,8 @@ export default class KeyBlock extends AbstractBlock {
 
 	constructor(component: Component, parent: Node, scope: TemplateScope, info: TemplateNode) {
 		super(component, parent, scope, info);
+		this.cannot_use_innerhtml();
+		this.not_static_content();
 
 		this.expression = new Expression(component, this, scope, info.expression);
 

src/compiler/compile/nodes/RawMustacheTag.ts

@@ -2,4 +2,9 @@ import Tag from './shared/Tag';
 
 export default class RawMustacheTag extends Tag {
 	type: 'RawMustacheTag';
+	constructor(component, parent, scope, info) {
+		super(component, parent, scope, info);
+		this.cannot_use_innerhtml();
+		this.not_static_content();
+	}
 }

src/compiler/compile/nodes/Slot.ts

@@ -60,5 +60,8 @@ export default class Slot extends Element {
 		}
 
 		component.slots.set(this.slot_name, this);
+
+		this.cannot_use_innerhtml();
+		this.not_static_content();
 	}
 }

src/compiler/compile/nodes/Text.ts

@@ -18,6 +18,7 @@ const elements_without_text = new Set([
 ]);
 
 const regex_ends_with_svg = /svg$/;
+const regex_non_whitespace_characters = /[\S\u00A0]/;
 
 export default class Text extends Node {
 	type: 'Text';
@@ -63,4 +64,11 @@ export default class Text extends Node {
 
 		return false;
 	}
+
+	use_space(): boolean {
+		if (this.component.compile_options.preserveWhitespace) return false;
+		if (regex_non_whitespace_characters.test(this.data)) return false;
+
+		return !this.within_pre();
+	}
 }

src/compiler/compile/nodes/shared/Expression.ts

@@ -197,6 +197,15 @@ export default class Expression {
 		});
 	}
 
+	dynamic_contextual_dependencies() {
+		return Array.from(this.contextual_dependencies).filter(name => {
+			return Array.from(this.template_scope.dependencies_for_name.get(name)).some(variable_name => {
+				const variable = this.component.var_lookup.get(variable_name);
+				return is_dynamic(variable);
+			});
+		});
+	}
+
 	// TODO move this into a render-dom wrapper?
 	manipulate(block?: Block, ctx?: string | void) {
 		// TODO ideally we wouldn't end up calling this method

src/compiler/compile/nodes/shared/Node.ts

@@ -15,6 +15,7 @@ export default class Node {
 	next?: INode;
 
 	can_use_innerhtml: boolean;
+	is_static_content: boolean;
 	var: string;
 	attributes: Attribute[];
 
@@ -33,6 +34,9 @@ export default class Node {
 				value: parent
 			}
 		});
+
+		this.can_use_innerhtml = true;
+		this.is_static_content = true;
 	}
 
 	cannot_use_innerhtml() {
@@ -42,6 +46,11 @@ export default class Node {
 		}
 	}
 
+	not_static_content() {
+		this.is_static_content = false;
+		if (this.parent) this.parent.not_static_content();
+	}
+
 	find_nearest(selector: RegExp) {
 		if (selector.test(this.type)) return this;
 		if (this.parent) return this.parent.find_nearest(selector);

src/compiler/compile/nodes/shared/Tag.ts

@@ -8,11 +8,22 @@ export default class Tag extends Node {
 
 	constructor(component, parent, scope, info) {
 		super(component, parent, scope, info);
+		component.tags.push(this);
+		this.cannot_use_innerhtml();
+
 		this.expression = new Expression(component, this, scope, info.expression);
 
 		this.should_cache = (
 			info.expression.type !== 'Identifier' ||
 			(this.expression.dependencies.size && scope.names.has(info.expression.name))
 		);
 	}
+	is_dependencies_static() {
+		return this.expression.dynamic_contextual_dependencies().length === 0 && this.expression.dynamic_dependencies().length === 0;
+	}
+	check_if_content_dynamic() {
+		if (!this.is_dependencies_static()) {
+			this.not_static_content();
+		}
+	}
 }

src/compiler/compile/render_dom/wrappers/AwaitBlock.ts

@@ -143,9 +143,6 @@ export default class AwaitBlockWrapper extends Wrapper {
 	) {
 		super(renderer, block, parent, node);
 
-		this.cannot_use_innerhtml();
-		this.not_static_content();
-
 		block.add_dependencies(this.node.expression.dependencies);
 
 		let is_dynamic = false;

src/compiler/compile/render_dom/wrappers/Comment.ts

@@ -38,4 +38,10 @@ export default class CommentWrapper extends Wrapper {
 			parent_node
 		);
 	}
+
+	text() {
+	    if (!this.renderer.options.preserveComments) return '';
+
+		return `<!--${this.node.data}-->`;
+	}
 }

src/compiler/compile/render_dom/wrappers/EachBlock.ts

@@ -80,8 +80,6 @@ export default class EachBlockWrapper extends Wrapper {
 		next_sibling: Wrapper
 	) {
 		super(renderer, block, parent, node);
-		this.cannot_use_innerhtml();
-		this.not_static_content();
 
 		const { dependencies } = node.expression;
 		block.add_dependencies(dependencies);

src/compiler/compile/render_dom/wrappers/Element/Attribute.ts

@@ -36,9 +36,6 @@ export class BaseAttributeWrapper {
 		this.parent = parent;
 
 		if (node.dependencies.size > 0) {
-			parent.cannot_use_innerhtml();
-			parent.not_static_content();
-
 			block.add_dependencies(node.dependencies);
 		}
 	}