Fix promlint order algorithm not work issue

[RainbowMango]

The less function provided to sort.SliceStable not work well. Since we should start to compare Text only if the two Metric are equal.

	// Ensure deterministic output.
	sort.SliceStable(problems, func(i, j int) bool {
		if problems[i].Metric < problems[j].Metric {
			return true
		} 

		return problems[i].Text < problems[j].Text
	})

Signed-off-by: RainbowMango [email protected]

[RainbowMango]

/cc @brancz
I happened to see this issue when I try to lint metrics from Kubernetes.

[brancz]

lgtm

[simonpasquier]

It can be even shorter/cleaner IMO:

	sort.SliceStable(problems, func(i, j int) bool {
		if problems[i].Metric == problems[j].Metric {
			return problems[i].Text < problems[j].Text
		}

		return problems[i].Metric < problems[j].Metric
	})

[RainbowMango]

By the way, I don't think we need to define a new type of problems here:

prometheus/util/promlint/promlint.go

Lines 43 to 54 in 0a0a228

	// problems is a slice of Problems with a helper method to easily append
	// additional Problems to the slice.
	type problems []Problem
	// Add appends a new Problem to the slice for the specified metric, with
	// the specified issue text.
	func (p *problems) Add(mf dto.MetricFamily, text string) {
	*p = append(*p, Problem{
	Metric: mf.GetName(),
	Text: text,
	})
	}

If people using a Goland IDE, and Goland always complains Receiver 'problems' may be 'nil' in call in place of involving Add() function. This is anti-pattern? How do you think?

prometheus/util/promlint/promlint.go

Line 126 in 0a0a228

problems.Add(mf, "no help text")