src/vs/platform/files/common/inMemoryFilesystemProvider.ts/InMemoryFileSystemProvider/_lookupAsDirectory
class InMemoryFileSystemProvider:	private _lookupAsDirectory(uri: URI, silent: boolean): Directory {
		const entry = this._lookup(uri, silent);
		if (entry instanceof Directory) {
			return entry;
		}
		throw new FileSystemProviderError('file not a directory', FileSystemProviderErrorCode.FileNotADirectory);
	}