fix: don't emit HTML warnings in custom renderer compile

packages/svelte/src/compiler/phases/2-analyze/visitors/ExpressionTag.js

@@ -11,7 +11,7 @@ import { mark_subtree_dynamic } from './shared/fragment.js';
 export function ExpressionTag(node, context) {
 	const in_template = context.path.at(-1)?.type === 'Fragment';
 
-	if (in_template && context.state.parent_element) {
+	if (in_template && context.state.parent_element && !context.state.analysis.custom_renderer) {
 		const message = is_tag_valid_with_parent('#text', context.state.parent_element);
 		if (message) {
 			e.node_invalid_placement(node, message);

packages/svelte/src/compiler/phases/2-analyze/visitors/RegularElement.js

@@ -25,7 +25,10 @@ import { runes } from '../../../state.js';
  */
 export function RegularElement(node, context) {
 	validate_element(node, context);
-	check_element(node, context);
+
+	if (!context.state.analysis.custom_renderer) {
+		check_element(node, context);
+	}
 
 	node.metadata.path = [...context.path];
 	context.state.analysis.elements.push(node);
@@ -34,7 +37,9 @@ export function RegularElement(node, context) {
 	if (node.name === 'textarea' && node.fragment.nodes.length > 0) {
 		for (const attribute of node.attributes) {
 			if (attribute.type === 'Attribute' && attribute.name === 'value') {
-				e.textarea_invalid_content(node);
+				if (!context.state.analysis.custom_renderer) {
+					e.textarea_invalid_content(node);
+				}
 			}
 		}
 
@@ -160,7 +165,7 @@ export function RegularElement(node, context) {
 		mark_subtree_dynamic(context.path);
 	}
 
-	if (context.state.parent_element) {
+	if (context.state.parent_element && !context.state.analysis.custom_renderer) {
 		let past_parent = false;
 		let only_warn = false;
 		const ancestors = [context.state.parent_element];
@@ -221,7 +226,8 @@ export function RegularElement(node, context) {
 		context.state.analysis.source[node.end - 2] === '/' &&
 		!is_void(node_name) &&
 		!is_svg(node_name) &&
-		!is_mathml(node_name)
+		!is_mathml(node_name) &&
+		!context.state.analysis.custom_renderer
 	) {
 		w.element_invalid_self_closing_tag(node, node.name);
 	}

packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteElement.js

@@ -12,7 +12,10 @@ import { mark_subtree_dynamic } from './shared/fragment.js';
  */
 export function SvelteElement(node, context) {
 	validate_element(node, context);
-	check_element(node, context);
+
+	if (!context.state.analysis.custom_renderer) {
+		check_element(node, context);
+	}
 
 	node.metadata.path = [...context.path];
 	context.state.analysis.elements.push(node);

packages/svelte/src/compiler/phases/2-analyze/visitors/Text.js

@@ -16,7 +16,8 @@ export function Text(node, context) {
 	if (
 		parent.type === 'Fragment' &&
 		context.state.parent_element &&
-		regex_not_whitespace.test(node.data)
+		regex_not_whitespace.test(node.data) &&
+		!context.state.analysis.custom_renderer
 	) {
 		const message = is_tag_valid_with_parent('#text', context.state.parent_element);
 		if (message) {

packages/svelte/src/compiler/phases/2-analyze/visitors/shared/element.js

@@ -79,12 +79,12 @@ export function validate_element(node, context) {
 				validate_slot_attribute(context, attribute);
 			}
 
-			if (attribute.name === 'is') {
+			if (attribute.name === 'is' && !context.state.analysis.custom_renderer) {
 				w.attribute_avoid_is(attribute);
 			}
 
 			const correct_name = react_attributes.get(attribute.name);
-			if (correct_name) {
+			if (correct_name && !context.state.analysis.custom_renderer) {
 				w.attribute_invalid_property_name(attribute, attribute.name, correct_name);
 			}
 

packages/svelte/tests/custom-renderers/samples/no-html-warnings/_config.js

@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+// This test verifies that HTML-specific warnings and errors are NOT produced
+// when compiling with a custom renderer. All patterns in main.svelte would
+// normally trigger compile errors or warnings in standard HTML mode.
+// With a custom renderer, they should all be silently accepted.
+export default test({
+	compile_warnings: false
+});

packages/svelte/tests/custom-renderers/samples/no-html-warnings/main.svelte

@@ -0,0 +1,79 @@
+<script>
+	let text = $state('expression in table');
+	let show = $state(true);
+</script>
+
+<!-- 1. node_invalid_placement: <a> containing <a> -->
+<a><a>link</a></a>
+
+<!-- 2. node_invalid_placement: text inside <table> -->
+<table>text inside table</table>
+
+<!-- 3. node_invalid_placement: expression tag inside <table> -->
+<table>{text}</table>
+
+<!-- 4. element_invalid_self_closing_tag: self-closing non-void element -->
+<div />
+
+<!-- 5. textarea_invalid_content: textarea with both value attribute and children -->
+<textarea value={text}>child</textarea>
+
+<!-- 6. attribute_avoid_is: the `is` attribute -->
+<button is="my-button">custom element</button>
+
+<!-- 7. attribute_invalid_property_name: React-style className -->
+<div className="foo">className test</div>
+
+<!-- 8. attribute_invalid_property_name: React-style htmlFor -->
+<label htmlFor="input-id">htmlFor test</label>
+
+<!-- 9. a11y_accesskey: accesskey attribute -->
+<div accesskey="s">accesskey test</div>
+
+<!-- 10. a11y_autofocus: autofocus on input -->
+<input autofocus />
+
+<!-- 11. a11y_misplaced_scope: scope on div -->
+<div scope="col">misplaced scope</div>
+
+<!-- 12. a11y_positive_tabindex: positive tabindex -->
+<div tabindex="5">positive tabindex</div>
+
+<!-- 13. a11y_hidden: aria-hidden on heading -->
+<h1 aria-hidden="true">hidden heading</h1>
+
+<!-- 14. a11y_missing_attribute: img without alt -->
+<img src="test.png" />
+
+<!-- 15. a11y_unknown_aria_attribute: unknown aria attribute -->
+<div aria-describedat="foo">unknown aria</div>
+
+<!-- 16. a11y_no_redundant_roles: redundant role on nav -->
+<nav role="navigation">redundant role</nav>
+
+<!-- 17. a11y_figcaption_parent: figcaption outside figure -->
+<figcaption>orphan figcaption</figcaption>
+
+<!-- 18. a11y_distracting_elements: marquee -->
+<marquee>distracting</marquee>
+
+<!-- 19. a11y_consider_explicit_label: <a> without text -->
+<a href="https://example.com"></a>
+
+<!-- 20. a11y_label_has_associated_control: label without associated control -->
+<label>no control</label>
+
+<!-- 21. a11y_missing_content: empty h2 -->
+<h2></h2>
+
+<!-- 22. node_invalid_placement_ssr: invalid nesting inside conditional block -->
+<div>
+	{#if show}
+		<tr><td>conditional nesting</td></tr>
+	{/if}
+</div>
+
+<!-- 23. a11y via svelte:element: a11y warnings should also be suppressed on <svelte:element> -->
+<svelte:element this={"img"} src="test.png" />
+<svelte:element this={"div"} accesskey="s">accesskey on svelte:element</svelte:element>
+<svelte:element this={"h1"} aria-hidden="true">hidden svelte:element heading</svelte:element>

packages/svelte/tests/custom-renderers/shared.ts

@@ -1,3 +1,4 @@
+import * as fs from 'node:fs';
 import * as path from 'node:path';
 import { setImmediate } from 'node:timers/promises';
 import { assert } from 'vitest';
@@ -6,6 +7,7 @@ import { suite_with_variants, type BaseTest } from '../suite.js';
 import type { CompileOptions } from '#compiler';
 import renderer, { create_root, serialize, dispatch_event, dom_elements } from './renderer.js';
 import { writeFile } from 'node:fs/promises';
+import { globSync } from 'tinyglobby';
 
 export interface CustomRendererTest extends BaseTest {
 	html?: string;
@@ -14,6 +16,7 @@ export interface CustomRendererTest extends BaseTest {
 	context?: Map<any, any>;
 	error?: string;
 	compile_error?: string;
+	compile_warnings?: false;
 	runtime_error?: string;
 	warnings?: string[];
 	test?: (args: {
@@ -85,6 +88,20 @@ async function common_setup(
 		throw err;
 	}
 
+	if (config.compile_warnings === false) {
+		const output_dir = `${cwd}/_output/client`;
+		const warning_files = globSync('**/*.warnings.json', { cwd: output_dir });
+
+		for (const file of warning_files) {
+			const warnings = JSON.parse(fs.readFileSync(path.join(output_dir, file), 'utf-8'));
+			assert.deepEqual(
+				warnings,
+				[],
+				`Expected no compile warnings in ${file}, got: ${warnings.map((/** @type {any} */ w: any) => w.code).join(', ')}`
+			);
+		}
+	}
+
 	return compile_options;
 }