extensions/typescript-language-features/src/tsServer/bufferSyncSupport.ts/BufferSyncSupport/openTextDocument
class BufferSyncSupport:	public openTextDocument(document: vscode.TextDocument): boolean {
		if (!this.modeIds.has(document.languageId)) {
			return false;
		}
		const resource = document.uri;
		const filepath = this.client.normalizedPath(resource);
		if (!filepath) {
			return false;
		}

		if (this.syncedBuffers.has(resource)) {
			return true;
		}

		const syncedBuffer = new SyncedBuffer(document, filepath, this.client, this.synchronizer);
		this.syncedBuffers.set(resource, syncedBuffer);
		syncedBuffer.open();
		this.requestDiagnostic(syncedBuffer);
		return true;
	}