[feat] Make setContext return the value that was passed in (#7432)

* return value from setContext

* update docs

* Add test

* eof new line

* pacify the linter

* const and tabs

site/content/docs/03-run-time.md

@@ -148,7 +148,7 @@ setContext(key: any, context: any)
 
 ---
 
-Associates an arbitrary `context` object with the current component and the specified `key`. The context is then available to children of the component (including slotted content) with `getContext`.
+Associates an arbitrary `context` object with the current component and the specified `key` and returns that object. The context is then available to children of the component (including slotted content) with `getContext`.
 
 Like lifecycle functions, this must be called during component initialisation.
 

src/runtime/internal/lifecycle.ts

@@ -46,8 +46,9 @@ export function createEventDispatcher<
 	};
 }
 
-export function setContext<T>(key, context: T) {
+export function setContext<T>(key, context: T): T {
 	get_current_component().$$.context.set(key, context);
+	return context;
 }
 
 export function getContext<T>(key): T {

test/runtime/samples/context-setcontext-return/_config.js

@@ -0,0 +1,5 @@
+export default {
+	html: `
+		<div>true</div>
+	`
+};

test/runtime/samples/context-setcontext-return/main.svelte

@@ -0,0 +1,7 @@
+<script>
+	import { setContext } from 'svelte';
+	const a = {};
+	const b = setContext('foo', a);
+</script>
+
+<div>{a === b}</div>