[API] Remove exported elements

[fantazio]

Clean up unused exported values, fields and constructors discovered using the dead_code_analyzer.

I was able to confirm that the removed elements are not used outside opam (in open source projects) by using Sherlocode and exploring the project's history. The following projects have been discarded from the search for uses outside opam because they are archived or have not been active for years: marracheck, opamfu, opam-build-revdeps, opam-lock, opam-package-upgrade.

Overall 366 elements have been cleaned up (71.5% of the elements reported by the analyzer).
In addition :

• one mistake was identified and fixed in src/client/opamConfigCommand.ml line 663;
• some types only used by cleaned up code are removed;
• some modules only containing cleaned up code are removed;
• the now unused parameter user_action has been silenced in src/state/opamSwitchState.ml line 982;
• one file is deleted (src/state/shellscripts/prompt.sh);
• the OpamHash and OpamSHA APIs have been simplified (a6ed337)

For more details about the process, a report is available here. You might mostly be interested in the final Results, the Methodology, and the "Informed cleanup" subsections for each component in the Detailed cleanup report.

I kept each commit focused on a single component (or subcomponent) and a single analyzer report section.

[fantazio]

Un-removed values that are used by dependencies:

• OpamPath.Switch.Default.bin by opam-rt
• OpamSysPoll.os_version by spectrum_capabilities
• OpamFilename.extract by opam-publish
• OpamFilename.remove_suffix by opam-bundle

The first 3 values are related to failures in the CI. The 4th was discovered by re-verifying uses of removed values from OpamFilename with Sherlocode.

There is an unbound value error in Depends-Linux jobs that comes from a change in #6827. I am not sure what to do of it.

[kit-ty-kate]

Hi, thanks for this experiment and maintaining dead_code_analyzer, it's been extremely useful on a local wip branch to extract what i need from a library.

However i'm not sure about this PR. The opam codebase, while mainly used for the tool itself, is also exported as libraries so having unused functions is part of the job description. During development, very few of these type of functions actually ever need to be updated or causes us problem and if some do we usually realise it's not used and sometime remove them individually if they don't make sense anymore.

Our benchmark also seems to be showing that there isn't much to gain by removing these unused functions but i'm tempted to keep this PR open for a bit to have time to go through it and pick-and-choose the functions and values that do not make sense anymore.

[fantazio]

I understand. Thanks for the feedback.

To help you pick-and-choose, you may want to first have a look at

• the fix in src/client/opamConfigCommand.ml line 663,
• the removed deprecated value with_open_out_bin in OpamFilename,
• and the simplification of the OpamHash and OpamSHA APIs (with the 2 impacted calls in src/core/opamSWHID.ml and src/state/opamSysInteract.ml).

I suppose that, for the same reason, you would not be interested in a PR regarding optional arguments always/never used ? I might still experiment them on opam at some point to explore limits of the analyzer and write a report, but would not triage the results further then ;)

[kit-ty-kate]

I suppose that, for the same reason, you would not be interested in a PR regarding optional arguments always/never used ? I might still experiment them on opam at some point to explore limits of the analyzer and write a report, but would not triage the results further then ;)

Optional arguments could be interesting to pick-and-choose too so feel free to open it if you're planning to also do it anyway, there is no problem with keeping a PR open or opening it in the first place. Thanks again!