fix: deconflict generated names against globals (#9570)

fixes #9559

Author: Rich-Harris

.changeset/green-hounds-play.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: deconflict generated names against globals

packages/svelte/src/compiler/phases/scope.js

@@ -184,6 +184,10 @@ export class Scope {
 			declaration.references.push({ node, path });
 		} else if (this.#parent) {
 			this.#parent.reference(node, path);
+		} else {
+			// no declaration was found, and this is the top level scope,
+			// which means this is a global
+			this.root.conflicts.add(node.name);
 		}
 	}
 }

packages/svelte/tests/runtime-runes/samples/globals-deconflicted/_config.js

@@ -0,0 +1,15 @@
+import { test } from '../../test';
+
+export default test({
+	html: `<p>hello</p>`,
+
+	before_test: () => {
+		// @ts-expect-error
+		globalThis.frag = 'hello';
+	},
+
+	after_test: () => {
+		// @ts-expect-error
+		delete globalThis.frag;
+	}
+});

packages/svelte/tests/runtime-runes/samples/globals-deconflicted/main.svelte

@@ -0,0 +1 @@
+<p>{frag}</p>