fix: `customRenderer` as a global option and remove `without_renderer` (#18359)

Co-authored-by: Rich Harris <rich.harris@vercel.com>
Co-authored-by: Rich Harris <hello@rich-harris.dev>

documentation/docs/98-reference/.generated/compile-errors.md

@@ -1119,6 +1119,12 @@ A component can only have one `<%name%>` element
 Valid `<svelte:...>` tag names are %list%
 ```
 
+### svelte_options_customrenderer_disabled
+
+```
+`customRenderer` cannot be set in `<svelte:options>` unless the `experimental.customRenderer` compiler option is enabled
+```
+
 ### svelte_options_deprecated_tag
 
 ```

packages/svelte/messages/compile-errors/template.md

@@ -429,6 +429,10 @@ HTML restricts where certain elements can appear. In case of a violation the bro
 
 > Valid `<svelte:...>` tag names are %list%
 
+## svelte_options_customrenderer_disabled
+
+> `customRenderer` cannot be set in `<svelte:options>` unless the `experimental.customRenderer` compiler option is enabled
+
 ## svelte_options_deprecated_tag
 
 > "tag" option is deprecated — use "customElement" instead

packages/svelte/src/compiler/errors.js

@@ -1549,6 +1549,15 @@ export function svelte_meta_invalid_tag(node, list) {
 	e(node, 'svelte_meta_invalid_tag', `Valid \`<svelte:...>\` tag names are ${list}\nhttps://svelte.dev/e/svelte_meta_invalid_tag`);
 }
 
+/**
+ * `customRenderer` cannot be set in `<svelte:options>` unless the `experimental.customRenderer` compiler option is enabled
+ * @param {null | number | NodeLike} node
+ * @returns {never}
+ */
+export function svelte_options_customrenderer_disabled(node) {
+	e(node, 'svelte_options_customrenderer_disabled', `\`customRenderer\` cannot be set in \`<svelte:options>\` unless the \`experimental.customRenderer\` compiler option is enabled\nhttps://svelte.dev/e/svelte_options_customrenderer_disabled`);
+}
+
 /**
  * "tag" option is deprecated — use "customElement" instead
  * @param {null | number | NodeLike} node

packages/svelte/src/compiler/index.js

@@ -10,6 +10,7 @@ import { analyze_component, analyze_module } from './phases/2-analyze/index.js';
 import { transform_component, transform_module } from './phases/3-transform/index.js';
 import { validate_component_options, validate_module_options } from './validate-options.js';
 import * as state from './state.js';
+import * as e from './errors.js';
 export { default as preprocess } from './preprocess/index.js';
 export { print } from './print/index.js';
 
@@ -34,6 +35,32 @@ export function compile(source, options) {
 		...parsed_options
 	} = parsed.options || {};
 
+	// resolve the per-component custom renderer, taking `<svelte:options customRenderer={...} />`
+	// into account. The normalized option is always a function returning `string | null | undefined`
+	// (see `validate-options.js`). A string opts in to a specific renderer module, `null`/`false`
+	// opts out to plain DOM (while keeping the feature enabled) and `true`/absent inherits whatever
+	// the global option resolves to.
+	let custom_renderer_option = validated.experimental.customRenderer;
+
+	if (custom_renderer !== undefined) {
+		// the feature is a global compiler option — a component can only override the renderer it uses
+		// (or opt out) when `experimental.customRenderer` is enabled. Otherwise nothing pushes a
+		// renderer, so allowing `<svelte:options customRenderer>` would silently do the wrong thing.
+		if (!options.experimental?.customRenderer && parsed.options?.attributes) {
+			for (const attribute of parsed.options.attributes) {
+				if (attribute.name === 'customRenderer') {
+					e.svelte_options_customrenderer_disabled(attribute);
+				}
+			}
+		}
+
+		if (typeof custom_renderer === 'string') {
+			custom_renderer_option = () => custom_renderer;
+		} else if (custom_renderer === false || custom_renderer === null) {
+			custom_renderer_option = () => null;
+		}
+	}
+
 	/** @type {ValidatedCompileOptions} */
 	const combined_options = {
 		...validated,
@@ -43,7 +70,7 @@ export function compile(source, options) {
 		runes: 'runes' in parsed_options ? () => parsed_options.runes : validated.runes,
 		experimental: {
 			...validated.experimental,
-			...(custom_renderer !== undefined ? { customRenderer: () => custom_renderer } : {})
+			customRenderer: custom_renderer_option
 		}
 	};
 

packages/svelte/src/compiler/phases/1-parse/read/options.js

@@ -197,7 +197,10 @@ export default function read_options(node) {
 		}
 	}
 
-	if (component_options.css === 'injected' && component_options.customRenderer !== undefined) {
+	if (
+		component_options.css === 'injected' &&
+		typeof component_options.customRenderer === 'string'
+	) {
 		// Find the css attribute node for the error position
 		const css_attribute = node.attributes.find(
 			(/** @type {any} */ a) => a.type === 'Attribute' && a.name === 'css'

packages/svelte/src/compiler/phases/2-analyze/index.js

@@ -472,7 +472,9 @@ export function analyze_component(root, source, options) {
 	const css = options.css({ filename: options.filename });
 	const custom_renderer = options.experimental.customRenderer?.({ filename: options.filename });
 
-	if (css === 'injected' && custom_renderer !== undefined) {
+	// only an actual renderer module (a string) is incompatible with injected css — a `null`
+	// renderer means the component renders to the DOM, which is fine
+	if (css === 'injected' && typeof custom_renderer === 'string') {
 		e.incompatible_with_custom_renderer(null, "`css: 'injected'`");
 	}
 

packages/svelte/src/compiler/phases/3-transform/client/transform-client.js

@@ -585,9 +585,14 @@ export function client_component(analysis, options) {
 		component_block.body.unshift(b.const(analysis.props_id, b.call('$.props_id')));
 	}
 
-	if (custom_renderer) {
+	if (custom_renderer !== undefined) {
+		// when the custom renderer feature is enabled every component pushes a renderer: components
+		// with a renderer module push `$renderer`, DOM components push `null`
 		component_block.body.unshift(
-			b.var('$$pop_renderer', b.call('$.push_renderer', b.id('$renderer')))
+			b.var(
+				'$$pop_renderer',
+				b.call('$.push_renderer', custom_renderer ? b.id('$renderer') : b.literal(null))
+			)
 		);
 		component_block.body.push(b.stmt(b.call('$$pop_renderer')));
 	}

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/component.js

@@ -1,7 +1,7 @@
 /** @import { BlockStatement, Expression, ExpressionStatement, Identifier, MemberExpression, Pattern, Property, SequenceExpression, SourceLocation, Statement } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../../types.js' */
-import { dev, is_ignored, custom_renderer } from '../../../../../state.js';
+import { dev, is_ignored } from '../../../../../state.js';
 import { get_attribute_chunks, object } from '../../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { add_svelte_meta, build_bind_this, Memoizer, validate_binding } from '../shared/utils.js';
@@ -456,13 +456,6 @@ export function build_component(node, component_name, loc, context) {
 		};
 	}
 
-	if (custom_renderer) {
-		const prev = fn;
-		fn = (node_id) => {
-			return b.call('$.without_renderer', b.arrow([], prev(node_id)));
-		};
-	}
-
 	if (node.type !== 'SvelteSelf') {
 		// Component name itself could be blocked on async values
 		memoizer.check_blockers(node.metadata.expression);

packages/svelte/src/compiler/state.js

@@ -46,8 +46,14 @@ export let dev;
 
 export let runes = false;
 
-/** @type {string | null | undefined} */
+/**
-export let custom_renderer = null;
+ * The custom renderer for the component currently being compiled:
+ * - `string`: the renderer module path (the component uses a custom renderer)
+ * - `null`: the custom renderer feature is enabled but this component renders to the DOM
+ * - `undefined`: the custom renderer feature is off
+ * @type {string | null | undefined}
+ */
+export let custom_renderer = undefined;
 
 /** @type {(index: number) => Location} */
 export let locator;
@@ -142,7 +148,7 @@ export function is_ignored(node, code) {
 export function reset(state) {
 	dev = false;
 	runes = false;
-	custom_renderer = null;
+	custom_renderer = undefined;
 	component_name = UNKNOWN_FILENAME;
 	source = '';
 	source_lines = [];

packages/svelte/src/compiler/types/index.d.ts

@@ -239,18 +239,30 @@ export interface ModuleCompileOptions {
 		 */
 		async?: boolean;
 		/**
-		 * Path to a module that exports the custom renderer to use. When this is truthy templating mode will also be automatically set to `functional`
+		 * Enables custom renderers to be specified with `<svelte:options customRenderer="path/to/renderer/module" />`. Can be:
+		 *
+		 * - `true`, allowing components to individually opt in
+		 * - a string that points to a default custom renderer module. Individual components can override the default, or opt out with `<svelte:options customRenderer={null} />`
+		 * - a function that receives a `{ filename }` object and returns a custom renderer module path, or `null` if no custom renderer should be used
+		 *
+		 * A custom renderer module's default export must be an object created with `createRenderer`.
 		 */
-		customRenderer?: string | ((options: { filename: string }) => string | undefined);
+		customRenderer?:
+			| boolean
+			| string
+			| ((options: { filename: string }) => string | null | undefined);
 	};
 }
 
 // The following two somewhat scary looking types ensure that certain types are required but can be undefined still
 
-export type ValidatedModuleCompileOptions = Omit<Required<ModuleCompileOptions>, 'rootDir'> & {
+export type ValidatedModuleCompileOptions = Omit<
+	Required<ModuleCompileOptions>,
+	'rootDir' | 'experimental'
+> & {
 	rootDir: ModuleCompileOptions['rootDir'];
 	experimental: Required<Omit<Required<ModuleCompileOptions>['experimental'], 'customRenderer'>> & {
-		customRenderer: (options: { filename: string }) => string | undefined;
+		customRenderer: (options: { filename: string }) => string | null | undefined;
 	};
 };
 

packages/svelte/src/compiler/types/template.d.ts

@@ -85,7 +85,7 @@ export namespace AST {
 		preserveWhitespace?: boolean;
 		namespace?: Namespace;
 		css?: 'injected';
-		customRenderer?: string;
+		customRenderer?: string | boolean | null;
 		customElement?: {
 			tag?: string;
 			shadow?: 'open' | 'none' | ObjectExpression | undefined;

packages/svelte/src/compiler/validate-options.js

@@ -45,13 +45,34 @@ const common_options = {
 
 	experimental: object({
 		async: boolean(false),
-		customRenderer: parametric(
+		// `customRenderer` can be:
-			/** @type {(options: { filename: string }) => string | undefined} */ (() => undefined),
+		//  - `undefined`/`false`: the feature is off, components compile to plain DOM
+		//  - `true`: the feature is on, every component defaults to DOM (opt in via `<svelte:options>`)
+		//  - a string: the feature is on, every component defaults to that module (opt out via `<svelte:options>`)
+		//  - a function: the feature is on, the module is resolved lazily per file
+		// The normalized value is always a function returning `string | null | undefined` where
+		// `string` is the renderer module, `null` is "DOM but feature enabled" (push `null`) and
+		// `undefined` is "feature off" (no renderer pushed at all).
+		customRenderer: validator(
+			/** @type {(options: { filename: string }) => string | null | undefined} */ (() => undefined),
 			(input, keypath) => {
-				if (input != null && typeof input !== 'string') {
+				if (input === false) {
-					throw_error(`${keypath} should be a string, if specified`);
+					return () => undefined;
+				}
+
+				if (input === true) {
+					return () => null;
+				}
+
+				if (typeof input === 'string') {
+					return () => input;
 				}
-				return /** @type {string | undefined} */ (input);
+
+				if (typeof input === 'function') {
+					return input;
+				}
+
+				throw_error(`${keypath} should be true, a string or a function, if specified`);
 			}
 		)
 	})

packages/svelte/src/internal/client/custom-renderer/state.js

@@ -35,23 +35,3 @@ export function push_renderer(value) {
 		}
 	};
 }
-
-/**
- * @template T
- * @param {() => T} fn
- * @returns {T}
- */
-export function without_renderer(fn) {
-	if (current_renderer === null) {
-		return fn();
-	}
-
-	var previous_renderer = current_renderer;
-	current_renderer = null;
-
-	try {
-		return fn();
-	} finally {
-		current_renderer = previous_renderer;
-	}
-}

packages/svelte/src/internal/client/index.js

@@ -186,4 +186,4 @@ export {
 export { strict_equals, equals } from './dev/equality.js';
 export { log_if_contains_state } from './dev/console-log.js';
 export { invoke_error_boundary } from './error-handling.js';
-export { push_renderer, without_renderer } from './custom-renderer/state.js';
+export { push_renderer } from './custom-renderer/state.js';

packages/svelte/tests/validator/samples/svelte-options-customrenderer-disabled/_config.js

@@ -0,0 +1,3 @@
+import { test } from '../../test';
+
+export default test({});

packages/svelte/tests/validator/samples/svelte-options-customrenderer-disabled/errors.json

@@ -0,0 +1,14 @@
+[
+	{
+		"code": "svelte_options_customrenderer_disabled",
+		"message": "`customRenderer` cannot be set in `<svelte:options>` unless the `experimental.customRenderer` compiler option is enabled",
+		"start": {
+			"line": 1,
+			"column": 16
+		},
+		"end": {
+			"line": 1,
+			"column": 43
+		}
+	}
+]

packages/svelte/tests/validator/samples/svelte-options-customrenderer-disabled/input.svelte

@@ -0,0 +1,3 @@
+<svelte:options customRenderer="./renderer" />
+
+<div>hello</div>

packages/svelte/types/index.d.ts

@@ -1196,9 +1196,18 @@ declare module 'svelte/compiler' {
 			 */
 			async?: boolean;
 			/**
-			 * Path to a module that exports the custom renderer to use. When this is truthy templating mode will also be automatically set to `functional`
+			 * Enables custom renderers to be specified with `<svelte:options customRenderer="path/to/renderer/module" />`. Can be:
+			 *
+			 * - `true`, allowing components to individually opt in
+			 * - a string that points to a default custom renderer module. Individual components can override the default, or opt out with `<svelte:options customRenderer={null} />`
+			 * - a function that receives a `{ filename }` object and returns a custom renderer module path, or `null` if no custom renderer should be used
+			 *
+			 * A custom renderer module's default export must be an object created with `createRenderer`.
 			 */
-			customRenderer?: string | ((options: { filename: string }) => string | undefined);
+			customRenderer?:
+				| boolean
+				| string
+				| ((options: { filename: string }) => string | null | undefined);
 		};
 	}
 	/**
@@ -1248,7 +1257,7 @@ declare module 'svelte/compiler' {
 			preserveWhitespace?: boolean;
 			namespace?: Namespace;
 			css?: 'injected';
-			customRenderer?: string;
+			customRenderer?: string | boolean | null;
 			customElement?: {
 				tag?: string;
 				shadow?: 'open' | 'none' | ObjectExpression | undefined;
@@ -3516,9 +3525,18 @@ declare module 'svelte/types/compiler/interfaces' {
 			 */
 			async?: boolean;
 			/**
-			 * Path to a module that exports the custom renderer to use. When this is truthy templating mode will also be automatically set to `functional`
+			 * Enables custom renderers to be specified with `<svelte:options customRenderer="path/to/renderer/module" />`. Can be:
+			 *
+			 * - `true`, allowing components to individually opt in
+			 * - a string that points to a default custom renderer module. Individual components can override the default, or opt out with `<svelte:options customRenderer={null} />`
+			 * - a function that receives a `{ filename }` object and returns a custom renderer module path, or `null` if no custom renderer should be used
+			 *
+			 * A custom renderer module's default export must be an object created with `createRenderer`.
 			 */
-			customRenderer?: string | ((options: { filename: string }) => string | undefined);
+			customRenderer?:
+				| boolean
+				| string
+				| ((options: { filename: string }) => string | null | undefined);
 		};
 	}
 	/**