NewMultiLabelMap does not return an error so it's easy for someone to
pass an incorrect/unsupported metric type and serve invalid metrics to
Prometheus.
This would read as `metrics.Counter` and `metrics.Gauge` when used,
which seems readable enough; but if you think bare strings are better,
an alternative to this approach might be to verify string value in
`NewMultiLabelMap` and panic?
Updates tailscale/corp#22075
Signed-off-by: Anton Tolchanov <anton@tailscale.com>
And make NewMultiLabelMap panic earlier (at construction time)
if the comparable struct type T violates the documented rules,
rather than panicking at Add time.
Updates #cleanup
Change-Id: Ib1a03babdd501b8d699c4f18b1097a56c916c6d5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
