BUG/memory usage: OpamConsole.log and OpamFile.Stats

[hannesm]

Dear everyone,

thanks for your time to read this bug report.

So, I have an application (https://github.com/hannesm/maintenance-intent-filter) using opam as a library - and discovered there are some heavy memory usages.

The root cause are two things:

• (a) 84a3d28 (part of Implement CLI versioning #4316) which "queues up OpamConsole messages if OpamCoreConfig.set has not been called". Now, in my application there's nothing calling OpamCoreConfig.set -- so these messages are queued up forever.
• (b) OpamFile.Stats.read_files (a list of strings) getting extended in OpamFile.MakeIO().read_opt - and never gets cleared (nor uniquified)

I was wondering whether for (a) a bounded queue could be used? And for (b), could that be only added if r.print_stats is true -- otherwise these mutable lists are never used. Or could that code be removed entirely, if not used?

FWIW, in Stats.print there's an error:

  let print () =
    let aux kind = function
      | [] -> ()
      | l  ->
        OpamConsole.msg "%d files %s:\n  %s\n"
          (List.length !read_files) kind (String.concat "\n  " l)
    in
    aux "read" !read_files;
    aux "write" !write_files

The List.length uses always the !read_files - while it should use l.

If you can decide on acceptable ways forward for both (a) and (b), that would be fantastic.