From 7a1326be065501f82bd4994d532bc5f15e58ae72 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Mon, 27 May 2024 13:52:15 +0200
Subject: [PATCH] fix: handle `this` parameter in TypeScript-annotated
 functions (#11795)

fixes #11731
---
 .changeset/fresh-walls-bathe.md                   |  5 +++++
 .../phases/1-parse/remove_typescript_nodes.js     | 15 ++++++++++++++-
 .../runtime-runes/samples/typescript/main.svelte  |  4 ++++
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/fresh-walls-bathe.md

diff --git a/.changeset/fresh-walls-bathe.md b/.changeset/fresh-walls-bathe.md
new file mode 100644
index 0000000000..153e4671e4
--- /dev/null
+++ b/.changeset/fresh-walls-bathe.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: handle `this` parameter in TypeScript-annotated functions
diff --git a/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js b/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js
index bbcd4195d1..0475661aaf 100644
--- a/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js
+++ b/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js
@@ -1,6 +1,17 @@
 import { walk } from 'zimmerframe';
 import * as b from '../../utils/builders.js';
 
+/**
+ * @param {import('estree').FunctionExpression | import('estree').FunctionDeclaration} node
+ * @param {import('zimmerframe').Context<any, any>} context
+ */
+function remove_this_param(node, context) {
+	if (node.params[0]?.type === 'Identifier' && node.params[0].name === 'this') {
+		node.params.shift();
+	}
+	return context.next();
+}
+
 /** @type {import('zimmerframe').Visitors<any, null>} */
 const visitors = {
 	ImportDeclaration(node) {
@@ -71,7 +82,9 @@ const visitors = {
 			};
 		}
 		return node;
-	}
+	},
+	FunctionExpression: remove_this_param,
+	FunctionDeclaration: remove_this_param
 };
 
 /**
diff --git a/packages/svelte/tests/runtime-runes/samples/typescript/main.svelte b/packages/svelte/tests/runtime-runes/samples/typescript/main.svelte
index e991aa7533..3dbf0eeb6f 100644
--- a/packages/svelte/tests/runtime-runes/samples/typescript/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/typescript/main.svelte
@@ -2,6 +2,10 @@
 	interface Hello { message: 'hello' }
 	type Goodbye = { message: 'goodbye' };
 
+	function this_fn(this: any) {
+		console.log(this);
+	}
+
 	export type { Hello };
 </script>