From 9eefe34b2a83335917f52f94389f448f446095a8 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Sun, 28 Jul 2024 13:48:03 -0400
Subject: [PATCH] add each.metadata.keyed

---
 .../svelte/src/compiler/phases/2-analyze/index.js  |  7 +++++++
 .../phases/3-transform/client/visitors/template.js | 14 +++++++-------
 packages/svelte/src/compiler/phases/scope.js       |  1 +
 packages/svelte/src/compiler/types/template.d.ts   |  1 +
 4 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index aa1e43196f..aac76faa60 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -1547,6 +1547,13 @@ const common_visitors = {
 	},
 	RenderTag(node, context) {
 		context.next({ ...context.state, render_tag: node });
+	},
+	EachBlock(node) {
+		if (node.key) {
+			// treat `{#each items as item, i (i)}` as a normal indexed block, everything else as keyed
+			node.metadata.keyed =
+				node.key.type !== 'Identifier' || !node.index || node.key.name !== node.index;
+		}
 	}
 };
 
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js
index cf0fd231e5..7fe24c1013 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js
@@ -2409,10 +2409,7 @@ export const template_visitors = {
 
 		let flags = 0;
 
-		if (
-			node.key &&
-			(node.key.type !== 'Identifier' || !node.index || node.key.name !== node.index)
-		) {
+		if (node.metadata.keyed) {
 			flags |= EACH_KEYED;
 
 			if (node.index) {
@@ -2421,7 +2418,7 @@ export const template_visitors = {
 
 			// In runes mode, if key === item, we don't need to wrap the item in a source
 			const key_is_item =
-				node.key.type === 'Identifier' &&
+				/** @type {Expression} */ (node.key).type === 'Identifier' &&
 				node.context.type === 'Identifier' &&
 				node.context.name === node.key.name;
 
@@ -2614,8 +2611,11 @@ export const template_visitors = {
 		/** @type {Expression} */
 		let key_function = b.id('$.index');
 
-		if (node.key) {
-			const expression = /** @type {Expression} */ (context.visit(node.key, key_state));
+		if (node.metadata.keyed) {
+			const expression = /** @type {Expression} */ (
+				context.visit(/** @type {Expression} */ (node.key), key_state)
+			);
+
 			key_function = b.arrow([node.context, index], expression);
 		}
 
diff --git a/packages/svelte/src/compiler/phases/scope.js b/packages/svelte/src/compiler/phases/scope.js
index 1ba9851ee3..167f61e034 100644
--- a/packages/svelte/src/compiler/phases/scope.js
+++ b/packages/svelte/src/compiler/phases/scope.js
@@ -592,6 +592,7 @@ export function create_scopes(ast, root, allow_reactive_declarations, parent) {
 			}
 
 			node.metadata = {
+				keyed: false,
 				contains_group_binding: false,
 				array_name: needs_array_deduplication ? state.scope.root.unique('$$array') : null,
 				index: scope.root.unique('$$index'),
diff --git a/packages/svelte/src/compiler/types/template.d.ts b/packages/svelte/src/compiler/types/template.d.ts
index ec35a08227..e5bc072c1a 100644
--- a/packages/svelte/src/compiler/types/template.d.ts
+++ b/packages/svelte/src/compiler/types/template.d.ts
@@ -393,6 +393,7 @@ export interface EachBlock extends BaseNode {
 	index?: string;
 	key?: Expression;
 	metadata: {
+		keyed: boolean;
 		contains_group_binding: boolean;
 		/** Set if something in the array expression is shadowed within the each block */
 		array_name: Identifier | null;