Print the filename that failed validation

[sed-i]

Enhancement Proposal

It would be handy if cos-tool printed the filename of the file that failed validation when used e.g. like so:

find . -path '*/prometheus_alert_rules/*' -type f -exec ./cos-tool-amd64 --format promql lint {} +

Currently, the output from cos-tool looks like this:

error validating: yaml: unmarshal errors:
  line 1: field alert not found in type rulefmt.RuleGroups
  line 2: field expr not found in type rulefmt.RuleGroups
  line 3: field for not found in type rulefmt.RuleGroups
  line 4: field labels not found in type rulefmt.RuleGroups
  line 6: field annotations not found in type rulefmt.RuleGroups
failed

so it's impossible to know which file failed validation.

Related: canonical/observability#22