Check upon config load whether alerting rule template fields can be parsed

[juliusv]

A user got error parsing template __alert_GlimpseDNSHighLatency: template: __alert_GlimpseDNSHighLatency:1: unexpected "*" in operand; missing space? in the Alertmanager email message because they had {{$labels.quantile * 100}} in their alerting message template, which isn't valid in Go templates. Can we detect this sort of thing at configuration load time by test-parsing the SUMMARY and DESCRIPTION fields?

[fabxc]

We can add a parse+execute cycle to the promtool. Parsing alone doesn't guarantee that much for templates.
I'll look into that later today.

[codesome]

I have done some similar checks in #4277. Only catch is that it wont detect $labels.something_wrong, but would detect $something_wrong, and the one mentioned in the issue description.

I will open a PR for this.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.