From 4b84c4df3a8c07f0a992e255350eb97db36c5cf6 Mon Sep 17 00:00:00 2001
From: Yuichiro Yamashita <xydybaseball@gmail.com>
Date: Tue, 3 Jan 2023 12:48:06 +0900
Subject: [PATCH] [fix] Improve `is_promise` handling (#8162)

* correctly handle promises that are of function type

* add License

Co-authored-by: Vilsol <me@vil.so>
---
 src/runtime/internal/utils.ts                 |  4 +++-
 .../samples/await-function-promise/_config.js | 19 +++++++++++++++++++
 .../await-function-promise/main.svelte        |  7 +++++++
 3 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 test/runtime/samples/await-function-promise/_config.js
 create mode 100644 test/runtime/samples/await-function-promise/main.svelte

diff --git a/src/runtime/internal/utils.ts b/src/runtime/internal/utils.ts
index 8868e38ee2..8adb0c279b 100644
--- a/src/runtime/internal/utils.ts
+++ b/src/runtime/internal/utils.ts
@@ -10,8 +10,10 @@ export function assign<T, S>(tar: T, src: S): T & S {
 	return tar as T & S;
 }
 
+// Adapted from https://github.com/then/is-promise/blob/master/index.js
+// Distributed under MIT License https://github.com/then/is-promise/blob/master/LICENSE
 export function is_promise<T = any>(value: any): value is PromiseLike<T> {
-	return value && typeof value === 'object' && typeof value.then === 'function';
+	return !!value && (typeof value === 'object' || typeof value === 'function') && typeof value.then === 'function';
 }
 
 export function add_location(element, file, line, column, char) {
diff --git a/test/runtime/samples/await-function-promise/_config.js b/test/runtime/samples/await-function-promise/_config.js
new file mode 100644
index 0000000000..b6a9de6856
--- /dev/null
+++ b/test/runtime/samples/await-function-promise/_config.js
@@ -0,0 +1,19 @@
+const realPromise = Promise.resolve(42);
+
+const promise = () => {};
+promise.then = realPromise.then.bind(realPromise);
+promise.catch = realPromise.catch.bind(realPromise);
+
+export default {
+	props: {
+		promise
+	},
+
+	test({ assert, target }) {
+		return promise.then(() => {
+			assert.htmlEqual(target.innerHTML, `
+				<p>42</p>
+			`);
+		});
+	}
+};
diff --git a/test/runtime/samples/await-function-promise/main.svelte b/test/runtime/samples/await-function-promise/main.svelte
new file mode 100644
index 0000000000..aaefc6b782
--- /dev/null
+++ b/test/runtime/samples/await-function-promise/main.svelte
@@ -0,0 +1,7 @@
+<script>
+	export let promise;
+</script>
+
+{#await promise then value}
+	<p>{JSON.stringify(value)}</p>
+{/await}