extensions/git/src/git.ts/Repository/diffIndexWithHEAD
class Repository:	async diffIndexWithHEAD(path?: string): Promise<string | Change[]> {
		if (!path) {
			return await this.diffFiles(true);
		}

		const args = ['diff', '--cached', '--', sanitizePath(path)];
		const result = await this.exec(args);
		return result.stdout;
	}