feat(kit): add createAutoInserter function

packages/kit/index.ts

@@ -1,3 +1,4 @@
 export * from '@volar/language-service';
+export * from './lib/createAutoInserter';
 export * from './lib/createChecker';
 export * from './lib/createFormatter';

packages/kit/lib/createAutoInserter.ts

@@ -0,0 +1,54 @@
+import {
+	createLanguage,
+	createLanguageService,
+	createUriMap,
+	type LanguagePlugin,
+	type LanguageServicePlugin,
+} from '@volar/language-service';
+import * as ts from 'typescript';
+import { URI } from 'vscode-uri';
+import { createServiceEnvironment } from './createServiceEnvironment';
+
+export function createAutoInserter(
+	languages: LanguagePlugin<URI>[],
+	services: LanguageServicePlugin[],
+) {
+	let settings = {};
+
+	const fakeUri = URI.parse('file:///dummy.txt');
+	const env = createServiceEnvironment(() => settings);
+	const language = createLanguage(languages, createUriMap(false), () => {});
+	const languageService = createLanguageService(language, services, env, {});
+
+	return {
+		env,
+		autoInsert,
+		get settings() {
+			return settings;
+		},
+		set settings(v) {
+			settings = v;
+		},
+	};
+
+	async function autoInsert(textWithCursor: string, insertedText: string, languageId: string, cursor = '|') {
+		const cursorIndex = textWithCursor.indexOf(cursor);
+		if (cursorIndex === -1) {
+			throw new Error('Cursor marker not found in input text.');
+		}
+		const content = textWithCursor.slice(0, cursorIndex) + insertedText
+			+ textWithCursor.slice(cursorIndex + cursor.length);
+		const snapshot = ts.ScriptSnapshot.fromString(content);
+		language.scripts.set(fakeUri, snapshot, languageId);
+		const document = languageService.context.documents.get(fakeUri, languageId, snapshot);
+		return await languageService.getAutoInsertSnippet(
+			fakeUri,
+			document.positionAt(cursorIndex + insertedText.length),
+			{
+				rangeOffset: cursorIndex,
+				rangeLength: 0,
+				text: insertedText,
+			},
+		);
+	}
+}