feat: add parent hierarchy to `__svelte_meta` objects at dev time (#16255)

* feat: add parent hierarchy to `__svelte_meta` objects at dev time

This adds a `parent` property to the `__svelte_meta` properties that are added to elements at dev time. This property represents the closest non-element parent the element is related to. For example for `{#if ...}<div>foo</div>{/if}` the `parent` of the div would be the line/column of the if block.
The parent is recursive and goes upwards (through component boundaries) until the root component is reached, which has no parent.

part of #11389

* oops

* Apply suggestions from code review

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

* tweak

* original component tag

* make render appear in tree, keep tree in sync when rerenders occur

---------

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

.changeset/hot-buses-end.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+feat: add parent hierarchy to `__svelte_meta` objects

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

@@ -5,7 +5,7 @@ import { extract_identifiers } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { create_derived } from '../utils.js';
 import { get_value } from './shared/declarations.js';
-import { build_expression } from './shared/utils.js';
+import { build_expression, add_svelte_meta } from './shared/utils.js';
 
 /**
  * @param {AST.AwaitBlock} node
@@ -54,7 +54,7 @@ export function AwaitBlock(node, context) {
 	}
 
 	context.state.init.push(
-		b.stmt(
+		add_svelte_meta(
 			b.call(
 				'$.await',
 				context.state.node,
@@ -64,7 +64,9 @@ export function AwaitBlock(node, context) {
 					: b.null,
 				then_block,
 				catch_block
-			)
+			),
+			node,
+			'await'
 		)
 	);
 }

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

@@ -13,7 +13,7 @@ import { dev } from '../../../../state.js';
 import { extract_paths, object } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { get_value } from './shared/declarations.js';
-import { build_expression } from './shared/utils.js';
+import { build_expression, add_svelte_meta } from './shared/utils.js';
 
 /**
  * @param {AST.EachBlock} node
@@ -337,7 +337,7 @@ export function EachBlock(node, context) {
 		);
 	}
 
-	context.state.init.push(b.stmt(b.call('$.each', ...args)));
+	context.state.init.push(add_svelte_meta(b.call('$.each', ...args), node, 'each'));
 }
 
 /**

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

@@ -2,7 +2,7 @@
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import * as b from '#compiler/builders';
-import { build_expression } from './shared/utils.js';
+import { build_expression, add_svelte_meta } from './shared/utils.js';
 
 /**
  * @param {AST.IfBlock} node
@@ -74,7 +74,7 @@ export function IfBlock(node, context) {
 		args.push(b.id('$$elseif'));
 	}
 
-	statements.push(b.stmt(b.call('$.if', ...args)));
+	statements.push(add_svelte_meta(b.call('$.if', ...args), node, 'if'));
 
 	context.state.init.push(b.block(statements));
 }

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

@@ -2,7 +2,7 @@
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import * as b from '#compiler/builders';
-import { build_expression } from './shared/utils.js';
+import { build_expression, add_svelte_meta } from './shared/utils.js';
 
 /**
  * @param {AST.KeyBlock} node
@@ -15,6 +15,10 @@ export function KeyBlock(node, context) {
 	const body = /** @type {Expression} */ (context.visit(node.fragment));
 
 	context.state.init.push(
-		b.stmt(b.call('$.key', context.state.node, b.thunk(key), b.arrow([b.id('$$anchor')], body)))
+		add_svelte_meta(
+			b.call('$.key', context.state.node, b.thunk(key), b.arrow([b.id('$$anchor')], body)),
+			node,
+			'key'
+		)
 	);
 }

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

@@ -3,7 +3,7 @@
 /** @import { ComponentContext } from '../types' */
 import { unwrap_optional } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
-import { build_expression } from './shared/utils.js';
+import { add_svelte_meta, build_expression } from './shared/utils.js';
 
 /**
  * @param {AST.RenderTag} node
@@ -48,16 +48,22 @@ export function RenderTag(node, context) {
 		}
 
 		context.state.init.push(
-			b.stmt(b.call('$.snippet', context.state.node, b.thunk(snippet_function), ...args))
+			add_svelte_meta(
+				b.call('$.snippet', context.state.node, b.thunk(snippet_function), ...args),
+				node,
+				'render'
+			)
 		);
 	} else {
 		context.state.init.push(
-			b.stmt(
+			add_svelte_meta(
 				(node.expression.type === 'CallExpression' ? b.call : b.maybe_call)(
 					snippet_function,
 					context.state.node,
 					...args
-				)
+				),
+				node,
+				'render'
 			)
 		);
 	}

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

@@ -4,7 +4,12 @@
 import { dev, is_ignored } from '../../../../../state.js';
 import { get_attribute_chunks, object } from '../../../../../utils/ast.js';
 import * as b from '#compiler/builders';
-import { build_bind_this, memoize_expression, validate_binding } from '../shared/utils.js';
+import {
+	build_bind_this,
+	memoize_expression,
+	validate_binding,
+	add_svelte_meta
+} from '../shared/utils.js';
 import { build_attribute_value } from '../shared/element.js';
 import { build_event_handler } from './events.js';
 import { determine_slot } from '../../../../../utils/slot.js';
@@ -483,7 +488,8 @@ export function build_component(node, component_name, context) {
 		);
 	} else {
 		context.state.template.push_comment();
-		statements.push(b.stmt(fn(anchor)));
+
+		statements.push(add_svelte_meta(fn(anchor), node, 'component', { componentTag: node.name }));
 	}
 
 	return statements.length > 1 ? b.block(statements) : statements[0];

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

@@ -1,4 +1,4 @@
-/** @import { AssignmentExpression, Expression, ExpressionStatement, Identifier, MemberExpression, SequenceExpression, Literal, Super, UpdateExpression, Pattern } from 'estree' */
+/** @import { AssignmentExpression, Expression, Identifier, MemberExpression, SequenceExpression, Literal, Super, UpdateExpression, ExpressionStatement } from 'estree' */
 /** @import { AST, ExpressionMetadata } from '#compiler' */
 /** @import { ComponentClientTransformState, ComponentContext, Context } from '../../types' */
 import { walk } from 'zimmerframe';
@@ -7,7 +7,7 @@ import * as b from '#compiler/builders';
 import { sanitize_template_string } from '../../../../../utils/sanitize_template_string.js';
 import { regex_is_valid_identifier } from '../../../../patterns.js';
 import is_reference from 'is-reference';
-import { dev, is_ignored, locator } from '../../../../../state.js';
+import { dev, is_ignored, locator, component_name } from '../../../../../state.js';
 import { build_getter, create_derived } from '../../utils.js';
 
 /**
@@ -424,3 +424,34 @@ export function build_expression(context, expression, metadata, state = context.
 
 	return sequence;
 }
+
+/**
+ * Wraps a statement/expression with dev stack tracking in dev mode
+ * @param {Expression} expression - The function call to wrap (e.g., $.if, $.each, etc.)
+ * @param {{ start?: number }} node - AST node for location info
+ * @param {'component' | 'if' | 'each' | 'await' | 'key' | 'render'} type - Type of block/component
+ * @param {Record<string, number | string>} [additional] - Any additional properties to add to the dev stack entry
+ * @returns {ExpressionStatement} - Statement with or without dev stack wrapping
+ */
+export function add_svelte_meta(expression, node, type, additional) {
+	if (!dev) {
+		return b.stmt(expression);
+	}
+
+	const location = node.start !== undefined && locator(node.start);
+	if (!location) {
+		return b.stmt(expression);
+	}
+
+	return b.stmt(
+		b.call(
+			'$.add_svelte_meta',
+			b.arrow([], expression),
+			b.literal(type),
+			b.id(component_name),
+			b.literal(location.line),
+			b.literal(location.column),
+			additional && b.object(Object.entries(additional).map(([k, v]) => b.init(k, b.literal(v))))
+		)
+	);
+}

packages/svelte/src/compiler/state.js

@@ -16,6 +16,9 @@ export let warnings = [];
  */
 export let filename;
 
+/**
+ * The name of the component that is used in the `export default function ...` statement.
+ */
 export let component_name = '<unknown>';
 
 /**

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

@@ -1,4 +1,4 @@
-/** @import { ComponentContext } from '#client' */
+/** @import { ComponentContext, DevStackEntry } from '#client' */
 
 import { DEV } from 'esm-env';
 import { lifecycle_outside_component } from '../shared/errors.js';
@@ -11,6 +11,7 @@ import {
 } from './runtime.js';
 import { effect, teardown } from './reactivity/effects.js';
 import { legacy_mode_flag } from '../flags/index.js';
+import { FILENAME } from '../../constants.js';
 
 /** @type {ComponentContext | null} */
 export let component_context = null;
@@ -20,6 +21,43 @@ export function set_component_context(context) {
 	component_context = context;
 }
 
+/** @type {DevStackEntry | null} */
+export let dev_stack = null;
+
+/** @param {DevStackEntry | null} stack */
+export function set_dev_stack(stack) {
+	dev_stack = stack;
+}
+
+/**
+ * Execute a callback with a new dev stack entry
+ * @param {() => any} callback - Function to execute
+ * @param {DevStackEntry['type']} type - Type of block/component
+ * @param {any} component - Component function
+ * @param {number} line - Line number
+ * @param {number} column - Column number
+ * @param {Record<string, any>} [additional] - Any additional properties to add to the dev stack entry
+ * @returns {any}
+ */
+export function add_svelte_meta(callback, type, component, line, column, additional) {
+	const parent = dev_stack;
+
+	dev_stack = {
+		type,
+		file: component[FILENAME],
+		line,
+		column,
+		parent,
+		...additional
+	};
+
+	try {
+		return callback();
+	} finally {
+		dev_stack = parent;
+	}
+}
+
 /**
  * The current component function. Different from current component context:
  * ```html

packages/svelte/src/internal/client/dev/elements.js

@@ -2,6 +2,7 @@
 import { COMMENT_NODE, DOCUMENT_FRAGMENT_NODE, ELEMENT_NODE } from '#client/constants';
 import { HYDRATION_END, HYDRATION_START, HYDRATION_START_ELSE } from '../../../constants.js';
 import { hydrating } from '../dom/hydration.js';
+import { dev_stack } from '../context.js';
 
 /**
  * @param {any} fn
@@ -28,6 +29,7 @@ export function add_locations(fn, filename, locations) {
 function assign_location(element, filename, location) {
 	// @ts-expect-error
 	element.__svelte_meta = {
+		parent: dev_stack,
 		loc: { file: filename, line: location[0], column: location[1] }
 	};
 

packages/svelte/src/internal/client/dom/blocks/await.js

@@ -16,9 +16,11 @@ import { queue_micro_task } from '../task.js';
 import { HYDRATION_START_ELSE, UNINITIALIZED } from '../../../../constants.js';
 import {
 	component_context,
+	dev_stack,
 	is_runes,
 	set_component_context,
-	set_dev_current_component_function
+	set_dev_current_component_function,
+	set_dev_stack
 } from '../../context.js';
 
 const PENDING = 0;
@@ -45,6 +47,7 @@ export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 
 	/** @type {any} */
 	var component_function = DEV ? component_context?.function : null;
+	var dev_original_stack = DEV ? dev_stack : null;
 
 	/** @type {V | Promise<V> | typeof UNINITIALIZED} */
 	var input = UNINITIALIZED;
@@ -75,7 +78,10 @@ export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 			set_active_effect(effect);
 			set_active_reaction(effect); // TODO do we need both?
 			set_component_context(active_component_context);
-			if (DEV) set_dev_current_component_function(component_function);
+			if (DEV) {
+				set_dev_current_component_function(component_function);
+				set_dev_stack(dev_original_stack);
+			}
 		}
 
 		try {
@@ -107,7 +113,11 @@ export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 			}
 		} finally {
 			if (restore) {
-				if (DEV) set_dev_current_component_function(null);
+				if (DEV) {
+					set_dev_current_component_function(null);
+					set_dev_stack(null);
+				}
+
 				set_component_context(null);
 				set_active_reaction(null);
 				set_active_effect(null);

packages/svelte/src/internal/client/dom/blocks/svelte-element.js

@@ -18,7 +18,7 @@ import {
 import { set_should_intro } from '../../render.js';
 import { current_each_item, set_current_each_item } from './each.js';
 import { active_effect } from '../../runtime.js';
-import { component_context } from '../../context.js';
+import { component_context, dev_stack } from '../../context.js';
 import { DEV } from 'esm-env';
 import { EFFECT_TRANSPARENT, ELEMENT_NODE } from '#client/constants';
 import { assign_nodes } from '../template.js';
@@ -107,6 +107,7 @@ export function element(node, get_tag, is_svg, render_fn, get_namespace, locatio
 				if (DEV && location) {
 					// @ts-expect-error
 					element.__svelte_meta = {
+						parent: dev_stack,
 						loc: {
 							file: filename,
 							line: location[0],

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

@@ -1,6 +1,6 @@
 export { createAttachmentKey as attachment } from '../../attachments/index.js';
 export { FILENAME, HMR, NAMESPACE_SVG } from '../../constants.js';
-export { push, pop } from './context.js';
+export { push, pop, add_svelte_meta } from './context.js';
 export { assign, assign_and, assign_or, assign_nullish } from './dev/assign.js';
 export { cleanup_styles } from './dev/css.js';
 export { add_locations } from './dev/elements.js';

packages/svelte/src/internal/client/reactivity/effects.js

@@ -41,7 +41,7 @@ import { DEV } from 'esm-env';
 import { define_property } from '../../shared/utils.js';
 import { get_next_sibling } from '../dom/operations.js';
 import { derived } from './deriveds.js';
-import { component_context, dev_current_component_function } from '../context.js';
+import { component_context, dev_current_component_function, dev_stack } from '../context.js';
 
 /**
  * @param {'$effect' | '$effect.pre' | '$inspect'} rune
@@ -359,7 +359,11 @@ export function template_effect(fn, thunks = [], d = derived) {
  * @param {number} flags
  */
 export function block(fn, flags = 0) {
-	return create_effect(RENDER_EFFECT | BLOCK_EFFECT | flags, fn, true);
+	var effect = create_effect(RENDER_EFFECT | BLOCK_EFFECT | flags, fn, true);
+	if (DEV) {
+		effect.dev_stack = dev_stack;
+	}
+	return effect;
 }
 
 /**

packages/svelte/src/internal/client/reactivity/types.d.ts

@@ -1,4 +1,10 @@
-import type { ComponentContext, Dom, Equals, TemplateNode, TransitionManager } from '#client';
+import type {
+	ComponentContext,
+	DevStackEntry,
+	Equals,
+	TemplateNode,
+	TransitionManager
+} from '#client';
 
 export interface Signal {
 	/** Flags bitmask */
@@ -80,6 +86,8 @@ export interface Effect extends Reaction {
 	parent: Effect | null;
 	/** Dev only */
 	component_function?: any;
+	/** Dev only. Only set for certain block effects. Contains a reference to the stack that represents the render tree */
+	dev_stack?: DevStackEntry | null;
 }
 
 export type Source<V = unknown> = Value<V>;

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

@@ -34,12 +34,13 @@ import { tracing_expressions, get_stack } from './dev/tracing.js';
 import {
 	component_context,
 	dev_current_component_function,
+	dev_stack,
 	is_runes,
 	set_component_context,
-	set_dev_current_component_function
+	set_dev_current_component_function,
+	set_dev_stack
 } from './context.js';
 import { handle_error, invoke_error_boundary } from './error-handling.js';
-import { snapshot } from '../shared/clone.js';
 
 let is_flushing = false;
 
@@ -444,6 +445,9 @@ export function update_effect(effect) {
 	if (DEV) {
 		var previous_component_fn = dev_current_component_function;
 		set_dev_current_component_function(effect.component_function);
+		var previous_stack = /** @type {any} */ (dev_stack);
+		// only block effects have a dev stack, keep the current one otherwise
+		set_dev_stack(effect.dev_stack ?? dev_stack);
 	}
 
 	try {
@@ -478,6 +482,7 @@ export function update_effect(effect) {
 
 		if (DEV) {
 			set_dev_current_component_function(previous_component_fn);
+			set_dev_stack(previous_stack);
 		}
 	}
 }

packages/svelte/src/internal/client/types.d.ts

@@ -187,4 +187,13 @@ export type SourceLocation =
 	| [line: number, column: number]
 	| [line: number, column: number, SourceLocation[]];
 
+export interface DevStackEntry {
+	file: string;
+	type: 'component' | 'if' | 'each' | 'await' | 'key' | 'render';
+	line: number;
+	column: number;
+	parent: DevStackEntry | null;
+	componentTag?: string;
+}
+
 export * from './reactivity/types';

packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/_config.js

@@ -0,0 +1,186 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client', 'hydrate'],
+	compileOptions: {
+		dev: true
+	},
+	html: `
+		<p>no parent</p>
+		<button>toggle</button>
+		<p>if</p>
+		<p>each</p>
+		<p>loading</p>
+		<p>key</p>
+		<p>hi</p>
+		<p>hi</p>
+		<p>hi</p>
+		<p>hi</p>
+		<p>hi</p>
+	`,
+
+	async test({ target, assert }) {
+		function check() {
+			const [main, if_, each, await_, key, child1, child2, child3, child4, dynamic] =
+				target.querySelectorAll('p');
+
+			// @ts-expect-error
+			assert.deepEqual(main.__svelte_meta.parent, null);
+
+			// @ts-expect-error
+			assert.deepEqual(if_.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'if',
+				line: 12,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(each.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'each',
+				line: 16,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(await_.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'await',
+				line: 20,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(key.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'key',
+				line: 26,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(child1.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'component',
+				componentTag: 'Child',
+				line: 30,
+				column: 0,
+				parent: null
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(child2.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'component',
+				componentTag: 'Child',
+				line: 33,
+				column: 1,
+				parent: {
+					file: 'passthrough.svelte',
+					type: 'render',
+					line: 5,
+					column: 0,
+					parent: {
+						file: 'main.svelte',
+						type: 'component',
+						componentTag: 'Passthrough',
+						line: 32,
+						column: 0,
+						parent: null
+					}
+				}
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(child3.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'component',
+				componentTag: 'Child',
+				line: 38,
+				column: 2,
+				parent: {
+					file: 'passthrough.svelte',
+					type: 'render',
+					line: 5,
+					column: 0,
+					parent: {
+						file: 'main.svelte',
+						type: 'component',
+						componentTag: 'Passthrough',
+						line: 37,
+						column: 1,
+						parent: {
+							file: 'passthrough.svelte',
+							type: 'render',
+							line: 5,
+							column: 0,
+							parent: {
+								file: 'main.svelte',
+								type: 'component',
+								componentTag: 'Passthrough',
+								line: 36,
+								column: 0,
+								parent: null
+							}
+						}
+					}
+				}
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(child4.__svelte_meta.parent, {
+				file: 'passthrough.svelte',
+				type: 'render',
+				line: 8,
+				column: 1,
+				parent: {
+					file: 'passthrough.svelte',
+					type: 'if',
+					line: 7,
+					column: 0,
+					parent: {
+						file: 'main.svelte',
+						type: 'component',
+						componentTag: 'Passthrough',
+						line: 43,
+						column: 1,
+						parent: {
+							file: 'main.svelte',
+							type: 'if',
+							line: 42,
+							column: 0,
+							parent: null
+						}
+					}
+				}
+			});
+
+			// @ts-expect-error
+			assert.deepEqual(dynamic.__svelte_meta.parent, {
+				file: 'main.svelte',
+				type: 'component',
+				componentTag: 'x.y',
+				line: 50,
+				column: 0,
+				parent: null
+			});
+		}
+
+		await tick();
+		check();
+
+		// Test that stack is kept when re-rendering
+		const button = target.querySelector('button');
+		button?.click();
+		await tick();
+		button?.click();
+		await tick();
+		check();
+	}
+});

packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/child.svelte

@@ -0,0 +1 @@
+<p>hi</p>

packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/main.svelte

@@ -0,0 +1,50 @@
+<script>
+	import Child from "./child.svelte";
+	import Passthrough from "./passthrough.svelte";
+	let x = { y: Child }
+	let key = 'test';
+	let show = $state(true);
+</script>
+
+<p>no parent</p>
+<button onclick={() => show = !show}>toggle</button>
+
+{#if true}
+	<p>if</p>
+{/if}
+
+{#each [1]}
+	<p>each</p>
+{/each}
+
+{#await Promise.resolve()}
+	<p>loading</p>
+{:then}
+	<p>await</p>
+{/await}
+
+{#key key}
+	<p>key</p>
+{/key} 
+
+<Child />
+
+<Passthrough>
+	<Child />
+</Passthrough>
+
+<Passthrough>
+	<Passthrough>
+		<Child />
+	</Passthrough>
+</Passthrough>
+
+{#if show}
+	<Passthrough>
+		{#snippet named()}
+			<p>hi</p>
+		{/snippet}
+	</Passthrough>
+{/if}
+
+<x.y />

packages/svelte/tests/runtime-runes/samples/svelte-meta-parent/passthrough.svelte

@@ -0,0 +1,9 @@
+<script>
+	let { children, named } = $props();
+</script>
+
+{@render children?.()}
+
+{#if true}
+	{@render named?.()}
+{/if}