grok vague error message when a capture pattern has a field name

[chrismo]

Semi-related to #5605, from an example used there:

$ super -z -c 'yield "foo bar" | grok("%{WORD}", this)'
error({message:"grok(): value does not match pattern",on:"foo bar"})

The error message is a bit vague as to the problem when I have no named capture patterns (if "named capture patterns" is the right nomenclature). If it could mention the missing field_name, that'd be nice.

[philrz]

Hi @chrismo. Hopefully I covered this adequately in my responses to your other questions here. In brief, if it was our intent to require at least one named field in every pattern p parameter to grok(), then I agree this error message would need to be to changed. However, since I believe the current behavior feels like a bug, I think if we make a fix it would no longer return an error in this situation. I'll hold this open and close it once that's confirmed.

[chrismo]

yeah, I answered that over there #5605 - I realize on its own now it's sorta silly - but this was in the context of building up a new pattern and wanting some indication that I'd got off to a good start. But I didn't make that clear when posting the issue.