fix: allow svelte:self in snippets

Author: paoloricciuti

packages/svelte/src/compiler/errors.js

@@ -141,7 +141,7 @@ const special_elements = {
 	/** @param {string} name */
 	'duplicate-svelte-element': (name) => `A component can only have one <${name}> element`,
 	'invalid-self-placement': () =>
-		`<svelte:self> components can only exist inside {#if} blocks, {#each} blocks, or slots passed to components`,
+		`<svelte:self> components can only exist inside {#if} blocks, {#each} blocks, {#snippet} blocks or slots passed to components`,
 	'missing-svelte-element-definition': () => `<svelte:element> must have a 'this' attribute`,
 	'missing-svelte-component-definition': () => `<svelte:component> must have a 'this' attribute`,
 	'invalid-svelte-element-definition': () => `Invalid element definition — must be an {expression}`,

packages/svelte/src/compiler/phases/1-parse/state/element.js

@@ -331,7 +331,8 @@ function read_tag_name(parser) {
 			if (
 				fragment.type === 'IfBlock' ||
 				fragment.type === 'EachBlock' ||
-				fragment.type === 'Component'
+				fragment.type === 'Component' ||
+				fragment.type === 'SnippetBlock'
 			) {
 				legal = true;
 				break;

packages/svelte/tests/compiler-errors/samples/self-reference/_config.js

@@ -4,7 +4,7 @@ export default test({
 	error: {
 		code: 'invalid-self-placement',
 		message:
-			'<svelte:self> components can only exist inside {#if} blocks, {#each} blocks, or slots passed to components',
+			'<svelte:self> components can only exist inside {#if} blocks, {#each} blocks,, {#snippet} blocks or slots passed to components',
 		position: [1, 1]
 	}
 });