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

.changeset/hot-buses-end.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+feat: add parent hierarchy to \_\_svelte_meta objects at dev time

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

@@ -453,6 +453,9 @@ export function client_component(analysis, options) {
 		if (analysis.custom_element) {
 			to_remove.push(b.literal('$$host'));
 		}
+		if (dev) {
+			to_remove.push(b.literal('$$dev'));
+		}
 
 		component_block.body.unshift(
 			b.const(

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, with_dev_stack } from './shared/utils.js';
 
 /**
  * @param {AST.AwaitBlock} node
@@ -54,7 +54,7 @@ export function AwaitBlock(node, context) {
 	}
 
 	context.state.init.push(
-		b.stmt(
+		with_dev_stack(
 			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, with_dev_stack } 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('$.each', ...args)));
+	context.state.init.push(with_dev_stack(b.call('$.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, with_dev_stack } 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('$.if', ...args)));
+	statements.push(with_dev_stack(b.call('$.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, with_dev_stack } 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('$$anchor')], body)))
+		with_dev_stack(
+			b.call('$.key', context.state.node, b.thunk(key), b.arrow([b.id('$$anchor')], body)),
+			node,
+			'key'
+		)
 	);
 }

packages/svelte/src/compiler/phases/3-transform/client/visitors/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,
+	with_dev_stack
+} 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 +488,10 @@ export function build_component(node, component_name, context) {
 		);
 	} else {
 		context.state.template.push_comment();
-		statements.push(b.stmt(fn(anchor)));
+
+		statements.push(
+			with_dev_stack(fn(anchor), node, 'component', { componentTag: component_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, Pattern, CallExpression, Statement } 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, filename } from '../../../../../state.js';
 import { build_getter, create_derived } from '../../utils.js';
 
 /**
@@ -394,3 +394,37 @@ export function build_expression(context, expression, metadata, state = context.
 
 	return sequence;
 }
+
+/**
+ * Wraps a statement/expression with dev stack tracking in dev mode
+ * @param {CallExpression} call_expression - The function call to wrap (e.g., $.if, $.each, etc.)
+ * @param {{ start?: number }} node - AST node for location info
+ * @param {'component' | 'if' | 'each' | 'await' | 'key'} type - Type of block/component
+ * @param {Record<string, number | string>} [additional] - Any additional properties to add to the dev stack entry
+ * @returns {Statement} - Statement with or without dev stack wrapping
+ */
+export function with_dev_stack(call_expression, node, type, additional) {
+	if (!dev) {
+		return b.stmt(call_expression);
+	}
+
+	const location = node.start && locator(node.start);
+	if (!location) {
+		return b.stmt(call_expression);
+	}
+
+	// Wrap with dev stack tracking
+	return b.stmt(
+		b.call(
+			'$.with_dev_stack',
+			b.arrow([], b.block([b.stmt(call_expression)])),
+			b.literal(type),
+			b.literal(filename),
+			b.literal(location.line),
+			b.literal(location.column),
+			additional
+				? b.object(Object.entries(additional).map(([key, value]) => b.init(key, b.literal(value))))
+				: b.null
+		)
+	);
+}

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';
@@ -20,6 +20,44 @@ 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 {string} file - Source file
+ * @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 with_dev_stack(callback, type, file, line, column, additional) {
+	/** @type {DevStackEntry} */
+	const new_entry = {
+		type,
+		file,
+		line,
+		column,
+		parent: dev_stack,
+		...additional
+	};
+	const previous_stack = dev_stack;
+	dev_stack = new_entry;
+
+	try {
+		return callback();
+	} finally {
+		dev_stack = previous_stack;
+	}
+}
+
 /**
  * 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/snippet.js

@@ -5,7 +5,9 @@ import { EFFECT_TRANSPARENT, ELEMENT_NODE } from '#client/constants';
 import { branch, block, destroy_effect, teardown } from '../../reactivity/effects.js';
 import {
 	dev_current_component_function,
-	set_dev_current_component_function
+	dev_stack,
+	set_dev_current_component_function,
+	set_dev_stack
 } from '../../context.js';
 import { hydrate_next, hydrate_node, hydrating } from '../hydration.js';
 import { create_fragment_from_html } from '../reconciler.js';
@@ -61,14 +63,18 @@ export function snippet(node, get_snippet, ...args) {
  * @param {(node: TemplateNode, ...args: any[]) => void} fn
  */
 export function wrap_snippet(component, fn) {
+	var original_stack = dev_stack;
 	const snippet = (/** @type {TemplateNode} */ node, /** @type {any[]} */ ...args) => {
 		var previous_component_function = dev_current_component_function;
+		var previous_stack = dev_stack;
 		set_dev_current_component_function(component);
+		set_dev_stack(original_stack);
 
 		try {
 			return fn(node, ...args);
 		} finally {
 			set_dev_current_component_function(previous_component_function);
+			set_dev_stack(previous_stack);
 		}
 	};
 

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, with_dev_stack } 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/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';
+	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 +1,82 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client', 'hydrate'],
+	compileOptions: {
+		dev: true
+	},
+
+	html: `<p>no parent</p><p>if</p><p>each</p><p>loading</p><p>key</p><p>hi</p><p>hi</p>`,
+
+	async test({ target, assert }) {
+		await tick();
+		const [main, if_, each, await_, key, child1, child2] = 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: 10,
+			column: 0,
+			parent: null
+		});
+
+		// @ts-expect-error
+		assert.deepEqual(each.__svelte_meta.parent, {
+			file: 'main.svelte',
+			type: 'each',
+			line: 14,
+			column: 0,
+			parent: null
+		});
+
+		// @ts-expect-error
+		assert.deepEqual(await_.__svelte_meta.parent, {
+			file: 'main.svelte',
+			type: 'await',
+			line: 18,
+			column: 0,
+			parent: null
+		});
+
+		// @ts-expect-error
+		assert.deepEqual(key.__svelte_meta.parent, {
+			file: 'main.svelte',
+			type: 'key',
+			line: 24,
+			column: 0,
+			parent: null
+		});
+
+		// @ts-expect-error
+		assert.deepEqual(child1.__svelte_meta.parent, {
+			file: 'main.svelte',
+			type: 'component',
+			componentTag: 'Child',
+			line: 28,
+			column: 0,
+			parent: null
+		});
+
+		// @ts-expect-error
+		assert.deepEqual(child2.__svelte_meta.parent, {
+			file: 'main.svelte',
+			type: 'component',
+			componentTag: 'Child',
+			line: 31,
+			column: 1,
+			parent: {
+				file: 'main.svelte',
+				type: 'component',
+				componentTag: 'Passthrough',
+				line: 30,
+				column: 0,
+				parent: null
+			}
+		});
+	}
+});

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 +1,32 @@
+<script>
+	import Child from "./child.svelte";
+	import Passthrough from "./passthrough.svelte";
+
+	let key = 'test';
+</script>
+
+<p>no parent</p>
+
+{#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>

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

@@ -0,0 +1,5 @@
+<script>
+    let { children } = $props();
+</script>
+
+{@render children()}