There is a test that specifically said "double dashes are illegal" – it is intended to exercise a case that doesn't match this regex. Could you change it to use some other illegal character?

Also, please add the DCO sign-off, instructions are behind the Details link

It might also be useful to add a positive test like this: (line 1467)

    {
      testName: "Config with multiple dashes",
      config: `mappings:
- match: "*.fabio--requests.count"
  name: "fabio_requests_count"
  help: "Fabio request count"
  labels:
    hostname: "$1"`,
      mappings: mappings{
        {
          statsdMetric: "test.fabio--requests.count",
          name:         "fabio_requests_count",
          labels: map[string]string{
            "hostname": "test",
          },
        },
      },
    },              },

Something I am wondering: what happens if we accept a statsd metric with -- but have no mapping for it? Will it be transformed to a valid Prometheus metric?

In my super quick testing it seems like it gets dropped if there's no mapping:

level=debug ts=2021-06-17T16:51:00.278Z caller=line.go:214 msg="Bad line from StatsD" line=X
level=debug ts=2021-06-17T16:51:00.290Z caller=listener.go:73 msg="Incoming line" proto=udp line=--.count:0|c
level=debug ts=2021-06-17T16:51:00.290Z caller=listener.go:73 msg="Incoming line" proto=udp line=

A mapping for match: "--" is invalid.

level=error ts=2021-06-17T16:52:24.339Z caller=main.go:340 msg="error loading config" error="invalid match: --"

It seems reasonable enough to me but it's up to you folks!

Hmm, but for metrics with a single dash there is an automatic mapping. It will be very confusing to users if some metrics are mapped automatically but others are not. Do you feel up to extending the metric name escaping so that it handles this input?

Hey @matthiasr,it sounds like you folks know better than me to get this over the line. I don't write Go either so maybe I'm not the best to handle this if there's more to it than is already done 😅

I created a new issue for handling the default case: #389.