upcoming prometheus releases

[Anil Madhavapeddy <avsm2@xxxxxxxxx>]

Dear all,

A heads up about some PRs in mirage/prometheus. The core `prometheus` library 
has had a dependency on Lwt which was a bit unnecessary, since the core metrics 
gathering functions (such as incrementing integers or clocking) do not require 
any blocking.

However, changing the types will break all existing consumers, and so Thomas 
Leonard suggested that we do a two step release process:

- https://github.com/mirage/prometheus/pull/66 adds a forward-compatible 
Prometheus_lwt library that are just aliases, with deprecation warnings on the 
existing functions. It also adds _fn suffixed synchronous versions of some 
metrics. Users can either mechanically convert Lwt code, or just use the direct 
functions, as they prefer, with no other changes.  I intend to release this as 
version 2.0 and can be done quite soon.

- https://github.com/mirage/prometheus/pull/65 then performs the breaking 
change and moves Lwt out of the core, deleting deprecated functions. I am also 
reviewing https://github.com/mirage/prometheus/pull/46 to see if we can take 
the opportunity to have a prometheus-reporter package to ease the dependency on 
Cohttp. This would be version 3.0 once the main branch settles, and once this 
is done it's fairly straightforward to maintain other concurrency library 
collectors out of tree.

- After all this I'm looking at OCaml runtime events being exposed, which would 
bump the minimum OCaml version up to 5.2 or so. I'm assuming noone who wants 
new prometheus features is still on OCaml 4.x, but please do speak up if you 
are.

...and is there anything else anyone wants? I'll look over the backlog in 
https://github.com/mirage/prometheus/pulls while I'm here. Thanks to Thomas 
Leonard, Mark Elvers and Romain for discussions on the various PRs so far!

cheers,
Anil