Restrict refs to first 100

[BenBeattieHood]

exec will cause a buffer overflow if the result is >200kb (it's default maxBuffer). Ideally we'd use spawn instead here, as git should be treated as a subprocess rather than in-process; but there's also efficiency in just limiting the refs to the first 100 instead.

If you prefer, we could swap the _exec function to use spawn as below instead:

private async _exec(args: string[], cwd: string): Promise<string> => {
    const start = Date.now();
    const cmd = gitCommand;
    try {
        const result = await new Promise<string>((resolve, reject) => {
            const childProcess = spawn(cmd, args, { cwd });
            let stdout = '', stderr = '';
            childProcess.stdout.on('data', chunk => { stdout += chunk; });
            childProcess.stderr.on('data', chunk => { stderr += chunk; });
            childProcess
            .on('error', reject)
            .on('close', code => {
                if (code === 0) {
                    resolve(stdout);
                } else {
                    reject(stderr);
                }
            });
        });
        
        Tracer.verbose(`git command: ${cmd}. Output size: ${result.length} (${Date.now() - start}ms) ${cwd}`);
        return result;
    }
    catch (err) {
        Tracer.error(`git command failed: ${cmd} (${Date.now() - start}ms) ${cwd} ${err}`);
        throw err;
    }
}

[BenBeattieHood]

@huizhougit 🙏 (or, can we up the exec maxBuffer size? I need to use this in a monorepo, which would need >4.5mb buffer, so it's kinda large)

[huizhougit]

@BenBeattieHood thanks for looking into it. spawn sounds good to me. Would you mind making a PR?

[BenBeattieHood]

Sure thing - here you go: #88