store: add handling code for older Prometheus versions

[GiedriusS]

Handle older Prometheus versions that do not support match[]. Add
tests that cover new code. The new code is largely modeled after the
LabelValues() code.

It fixes #4586 (comment) and unblocks the release.

Signed-off-by: Giedrius Statkevičius [email protected]

[yeya24]

Code looks good but we still need to fix the test.

goroutine 1606 [running]:
testing.tRunner.func1.2(0x13c9620, 0x2003350)
	/usr/local/go/src/testing/testing.go:1143 +0x332
testing.tRunner.func1(0xc0629d7980)
	/usr/local/go/src/testing/testing.go:1146 +0x4b6
panic(0x13c9620, 0x2003350)
	/usr/local/go/src/runtime/panic.go:965 +0x1b9
github.com/thanos-io/thanos/pkg/store.(*PrometheusStore).LabelNames(0xc0004b3d60, 0x18024d0, 0xc0020cb380, 0xc0005c7f08, 0x0, 0x0, 0x0)
	/home/circleci/project/pkg/store/prometheus.go:512 +0x3e
github.com/thanos-io/thanos/pkg/store.TestPrometheusStore_LabelNames_e2e(0xc0629d7980)
	/home/circleci/project/pkg/store/prometheus_test.go:381 +0x965
testing.tRunner(0xc0629d7980, 0x15f9798)
	/usr/local/go/src/testing/testing.go:1193 +0xef
created by testing.(*T).Run
	/usr/local/go/src/testing/testing.go:1238 +0x2b3

We need to pass a version function to github.com/thanos-io/thanos/pkg/store.TestPrometheusStore_LabelNames_e2e

[GiedriusS]

Code looks good but we still need to fix the test.

goroutine 1606 [running]:
testing.tRunner.func1.2(0x13c9620, 0x2003350)
	/usr/local/go/src/testing/testing.go:1143 +0x332
testing.tRunner.func1(0xc0629d7980)
	/usr/local/go/src/testing/testing.go:1146 +0x4b6
panic(0x13c9620, 0x2003350)
	/usr/local/go/src/runtime/panic.go:965 +0x1b9
github.com/thanos-io/thanos/pkg/store.(*PrometheusStore).LabelNames(0xc0004b3d60, 0x18024d0, 0xc0020cb380, 0xc0005c7f08, 0x0, 0x0, 0x0)
	/home/circleci/project/pkg/store/prometheus.go:512 +0x3e
github.com/thanos-io/thanos/pkg/store.TestPrometheusStore_LabelNames_e2e(0xc0629d7980)
	/home/circleci/project/pkg/store/prometheus_test.go:381 +0x965
testing.tRunner(0xc0629d7980, 0x15f9798)
	/usr/local/go/src/testing/testing.go:1193 +0xef
created by testing.(*T).Run
	/usr/local/go/src/testing/testing.go:1238 +0x2b3

We need to pass a version function to github.com/thanos-io/thanos/pkg/store.TestPrometheusStore_LabelNames_e2e

Thank you! I have just deleted that test since it is now covered by TestPrometheusStore_LabelAPIs_e2e. I really need to add pre-commit hooks so that make test-local would be executed before committing because now I only ran the new test, and didn't catch this as a result :/

[yeya24]

LGTM!

[bwplotka]

Thanks for quick fix!