[feat] get all contexts (#6528)

* get all contexts

* docs

* explicit return type

* allow specifying return type through generic parameter

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

Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>
Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

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

@@ -200,6 +200,24 @@ Checks whether a given `key` has been set in the context of a parent component.
 </script>
 ```
 
+#### `getAllContexts`
+
+```js
+contexts: Map<any, any> = getAllContexts()
+```
+
+---
+
+Retrieves the whole context map that belongs to the closest parent component. Must be called during component initialisation. Useful, for example, if you programmatically create a component and want to pass the existing context to it.
+
+```sv
+<script>
+	import { getAllContexts } from 'svelte';
+
+	const contexts = getAllContexts();
+</script>
+```
+
 #### `createEventDispatcher`
 
 ```js

src/runtime/index.ts

@@ -7,6 +7,7 @@ export {
 	afterUpdate,
 	setContext,
 	getContext,
+	getAllContexts,
 	hasContext,
 	tick,
 	createEventDispatcher,

src/runtime/internal/lifecycle.ts

@@ -54,6 +54,10 @@ export function getContext<T>(key): T {
 	return get_current_component().$$.context.get(key);
 }
 
+export function getAllContexts<T extends Map<any, any> = Map<any, any>>(): T {
+	return get_current_component().$$.context;
+}
+
 export function hasContext(key): boolean {
 	return get_current_component().$$.context.has(key);	
 }

src/runtime/ssr.ts

@@ -1,6 +1,7 @@
 export {
 	setContext,
 	getContext,
+	getAllContexts,
 	hasContext,
 	tick,
 	createEventDispatcher,

test/runtime/samples/context-api-d/Leaf.svelte

@@ -0,0 +1,9 @@
+<script>
+	import { getAllContexts } from 'svelte';
+
+	const context = getAllContexts();
+</script>
+
+{#each [...context.keys()] as key}
+	<div>{key}: {context.get(key)}</div>
+{/each}

test/runtime/samples/context-api-d/Nested.svelte

@@ -0,0 +1,8 @@
+<script>
+	import { setContext } from 'svelte';
+  setContext('a', 1);
+  setContext('b', 2);
+  setContext('c', 3);
+</script>
+
+<slot></slot>

test/runtime/samples/context-api-d/_config.js

@@ -0,0 +1,7 @@
+export default {
+	html: `
+		<div>a: 1</div>
+		<div>b: 2</div>
+		<div>c: 3</div>
+	`
+};

test/runtime/samples/context-api-d/main.svelte

@@ -0,0 +1,8 @@
+<script>
+  import Nested from './Nested.svelte';
+  import Leaf from './Leaf.svelte';
+</script>
+
+<Nested>
+  <Leaf />
+</Nested>