allow <svelte:self> to be part of a slot (#4532)

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* Allow `<svelte:self>` to be used in a slot ([#2798](https://github.com/sveltejs/svelte/issues/2798))
 * Expose object of unknown props in `$$restProps` ([#2930](https://github.com/sveltejs/svelte/issues/2930))
 
 ## 3.19.2

src/compiler/parse/state/tag.ts

@@ -241,7 +241,7 @@ function read_tag_name(parser: Parser) {
 
 		while (i--) {
 			const fragment = parser.stack[i];
-			if (fragment.type === 'IfBlock' || fragment.type === 'EachBlock') {
+			if (fragment.type === 'IfBlock' || fragment.type === 'EachBlock' || fragment.type === 'InlineComponent') {
 				legal = true;
 				break;
 			}
@@ -250,7 +250,7 @@ function read_tag_name(parser: Parser) {
 		if (!legal) {
 			parser.error({
 				code: `invalid-self-placement`,
-				message: `<svelte:self> components can only exist inside if-blocks or each-blocks`
+				message: `<svelte:self> components can only exist inside {#if} blocks, {#each} blocks, or slots passed to components`
 			}, start);
 		}
 

test/parser/samples/error-self-reference/error.json

@@ -1,6 +1,6 @@
 {
 	"code": "invalid-self-placement",
-	"message": "<svelte:self> components can only exist inside if-blocks or each-blocks",
+	"message": "<svelte:self> components can only exist inside {#if} blocks, {#each} blocks, or slots passed to components",
 	"start": {
 		"line": 1,
 		"column": 1,

test/runtime/samples/self-reference-component/Countdown.svelte

@@ -0,0 +1,7 @@
+<script>
+	export let count;
+</script>
+
+{#if count > 0}
+	<slot count={count-1}></slot>
+{/if}

test/runtime/samples/self-reference-component/_config.js

@@ -0,0 +1,3 @@
+export default {
+	html: '5 4 3 2 1 0',
+};

test/runtime/samples/self-reference-component/main.svelte

@@ -0,0 +1,10 @@
+<script>
+	import Countdown from './Countdown.svelte';
+	export let count = 5;
+</script>
+
+{count}
+
+<Countdown {count} let:count={i}>
+	<svelte:self count={i} />
+</Countdown>