Add MustCollector API for pusher

[oiooj]

@kakkoyun PTAL

[kakkoyun]

@oiooj Could you please explain the justification behind this change? It's hard to understand without any context.

[oiooj]

Hi @kakkoyun , We use the pusher heavily, and we'll register many collectors with the pusher, but the pusher.Collector API only can register one collector at a time，and we can't get the error immediately, so the new API is more useful and convenient.

[kakkoyun]

I don't think adding an API that panics to the pusher is the right solution here.
If I'm not mistaken, I understand from you comment that you want to have an API to add multiple collectors. Would a simple for loop not satisfy your needs?

p := push.New("http://example.org/metrics", "my_job").
for _, c := range []prometheus.Collector{myCollector1, myCollector2} {
    p.Collector(myCollector1)
} 
p.Grouping("zone", "xy").Client(&myHTTPClient).BasicAuth("top", "secret").Add()

If somehow you don't want to use this, I might consider making Collector method variadic.

func (p *Pusher) Collector(collectors ...prometheus.Collector) *Pusher {
      if p.error != nil {
            return p
      }
       for _, c := range collectors {
            p.error = p.registerer.Register(c)		
            if p.error != nil {
                  return p
            }
	}
	return p
}

[oiooj]

Is myCollector1 registered successfully? We want to know the result when the collectors is being registered. Maybe that is why Registerer has the MustRegister API.

[kakkoyun]

I see what you mean. We can consider adding a method the obtain the error from outside. I just don't want to add a method that panics in the pusher. None of the other APIs in the package do it. I'd prefer to keep the consistent behaviour.

[oiooj]

New API #1075 merged, this PR closed.