better hydration for only html tag

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

@@ -415,13 +415,15 @@ export default class ElementWrapper extends Wrapper {
 
 		const { can_use_textcontent, can_optimise_to_html_string } = this.node;
 
+		const to_optimise_hydration = can_optimise_to_html_string || (!is_head(parent_node) && this.node.children.length === 1 && this.node.children[0].type === 'RawMustacheTag');
+
 		if (hydratable) {
 			if (parent_nodes) {
 				block.chunks.claim.push(b`
-					${node} = ${this.get_claim_statement(block, parent_nodes, can_optimise_to_html_string)};
+					${node} = ${this.get_claim_statement(block, parent_nodes, to_optimise_hydration)};
 				`);
 
-				if (!can_optimise_to_html_string && !this.void && this.node.children.length > 0) {
+				if (!to_optimise_hydration && !this.void && this.node.children.length > 0) {
 					block.chunks.claim.push(b`
 						var ${nodes} = ${children};
 					`);
@@ -534,7 +536,7 @@ export default class ElementWrapper extends Wrapper {
 		this.add_styles(block);
 		this.add_manual_style_scoping(block);
 
-		if (nodes && hydratable && !this.void && !can_optimise_to_html_string) {
+		if (nodes && hydratable && !this.void && !to_optimise_hydration) {
 			block.chunks.claim.push(
 				b`${this.node.children.length > 0 ? nodes : children}.forEach(@detach);`
 			);
@@ -570,7 +572,7 @@ export default class ElementWrapper extends Wrapper {
 		return x`@element(${reference})`;
 	}
 
-	get_claim_statement(block: Block, nodes: Identifier, can_optimise_to_html_string: boolean) {
+	get_claim_statement(block: Block, nodes: Identifier, to_optimise_hydration: boolean) {
 		const attributes = this.attributes
 			.filter((attr) => !(attr instanceof SpreadAttributeWrapper) && !attr.property_name)
 			.map((attr) => p`${(attr as StyleAttributeWrapper | AttributeWrapper).name}: true`);
@@ -588,7 +590,7 @@ export default class ElementWrapper extends Wrapper {
 			reference = x`(${this.node.tag_expr.manipulate(block)} || 'null').toUpperCase()`;
 		}
 
-		if (can_optimise_to_html_string) {
+		if (to_optimise_hydration) {
 			attributes.push(p`["data-svelte"]: true`);
 		}
 

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

@@ -9,6 +9,7 @@ import MustacheTag from '../../nodes/MustacheTag';
 import RawMustacheTag from '../../nodes/RawMustacheTag';
 import { is_head } from './shared/is_head';
 import { Identifier, Node } from 'estree';
+import hash from '../../utils/hash';
 
 export default class RawMustacheTagWrapper extends Tag {
 	var: Identifier = { type: 'Identifier', name: 'raw' };
@@ -35,7 +36,7 @@ export default class RawMustacheTagWrapper extends Tag {
 				content => insert(content)
 			);
 
-			block.chunks.mount.push(insert(init));
+			block.chunks.mount.push(b`if (@get_svelte_dataset(${parent_node}) !== "${hash(JSON.stringify(this.node.expression.node))}") ${insert(init)}`);
 		} else {
 			const needs_anchor = in_head || (this.next ? !this.next.is_dom_node() : (!this.parent || !this.parent.is_dom_node()));
 

src/compiler/compile/render_ssr/Renderer.ts

@@ -48,6 +48,7 @@ export interface RenderOptions extends CompileOptions{
 	locate: (c: number) => { line: number; column: number };
 	head_id?: string;
 	has_added_svelte_hash?: boolean;
+	optimised_html_hydration?: boolean;
 }
 
 export default class Renderer {

src/compiler/compile/render_ssr/handlers/Element.ts

@@ -10,6 +10,7 @@ import fix_attribute_casing from '../../render_dom/wrappers/Element/fix_attribut
 import { namespaces } from '../../../utils/namespaces';
 import { regex_starts_with_newline } from '../../../utils/patterns';
 import { Node, Expression as ESExpression } from 'estree';
+import hash from '../../utils/hash';
 
 export default function (node: Element, renderer: Renderer, options: RenderOptions) {
 
@@ -163,9 +164,10 @@ export default function (node: Element, renderer: Renderer, options: RenderOptio
 	if (options.hydratable) {
 		if (options.head_id) {
 			renderer.add_string(` data-svelte="${options.head_id}"`);
-		}
+		} else if (node.children.length === 1 && node.children[0].type === 'RawMustacheTag') {
-
+			renderer.add_string(` data-svelte="${hash(JSON.stringify(node.children[0].expression.node))}"`);
-		if (node.can_optimise_to_html_string && !options.has_added_svelte_hash) {
+			options = { ...options, optimised_html_hydration: true };
+		} else if (node.can_optimise_to_html_string && !options.has_added_svelte_hash) {
 			renderer.add_string(` data-svelte="${node.hash()}"`);
 			options = { ...options, has_added_svelte_hash: true };
 		}

src/compiler/compile/render_ssr/handlers/HtmlTag.ts

@@ -3,7 +3,7 @@ import RawMustacheTag from '../../nodes/RawMustacheTag';
 import { Expression } from 'estree';
 
 export default function(node: RawMustacheTag, renderer: Renderer, options: RenderOptions) {
-	if (options.hydratable) renderer.add_string('<!-- HTML_TAG_START -->');
+	if (options.hydratable && !options.optimised_html_hydration) renderer.add_string('<!-- HTML_TAG_START -->');
 	renderer.add_expression(node.expression.node as Expression);
-	if (options.hydratable) renderer.add_string('<!-- HTML_TAG_END -->');
+	if (options.hydratable && !options.optimised_html_hydration) renderer.add_string('<!-- HTML_TAG_END -->');
 }

test/runtime/index.ts

@@ -154,6 +154,7 @@ describe('runtime', () => {
 					window.SvelteComponent = SvelteComponent;
 
 					const target = window.document.querySelector('main');
+					let snapshot = undefined;
 
 					if (hydrate && from_ssr_html) {
 						// ssr into target
@@ -163,6 +164,11 @@ describe('runtime', () => {
 						const SsrSvelteComponent = require(`./samples/${dir}/main.svelte`).default;
 						const { html } = SsrSvelteComponent.render(config.props);
 						target.innerHTML = html;
+
+						if (config.snapshot) {
+							snapshot = config.snapshot(target);
+						}
+
 						delete compileOptions.generate;
 						if (config.after_test) config.after_test();
 					} else {
@@ -212,6 +218,7 @@ describe('runtime', () => {
 							component,
 							mod,
 							target,
+							snapshot,
 							window,
 							raf,
 							compileOptions

test/runtime/samples/raw-anchor-first-last-child/_config.js

@@ -3,11 +3,24 @@ export default {
 		raw: '<span>foo</span>'
 	},
 
-	test({ assert, component, target }) {
+	snapshot(target) {
+		const span = target.querySelector('span');
+
+		return {
+			span
+		};
+	},
+
+	test({ assert, component, target, snapshot }) {
 		const span = target.querySelector('span');
 		assert.ok(!span.previousSibling);
 		assert.ok(!span.nextSibling);
 
+		if (snapshot) {
+			assert.equal(span, snapshot.span);
+		}
+
 		component.raw = '<span>bar</span>';
+		assert.htmlEqual(target.innerHTML, '<div><span>bar</span></div>');
 	}
 };

test/runtime/samples/raw-mustaches-preserved/_config.js

@@ -11,7 +11,7 @@ export default {
 		const p = target.querySelector('p');
 
 		component.raw = '<p>does not change</p>';
-		assert.equal(target.innerHTML, '<div><p>does not change</p></div>');
+		assert.htmlEqual(target.innerHTML, '<div><p>does not change</p></div>');
 		assert.strictEqual(target.querySelector('p'), p);
 	}
 };