feat(promote): complete pending promotion files

[Alizter]

dune promote <TAB> now completes against the entries in the build dir's .to-promote db instead of falling back to no completion at all.

Adds a promote_file cmdliner conv in bin/promotion.ml whose completion func takes Common.Builder.term as the cmdliner context, runs Common.init to set up the workspace exactly as the run path does (so --root and --build-dir are honoured rather than hardcoded), and emits sorted cwd-relative paths via Path.reach so candidates display the same way the user would type them.

Adds a dune_complete helper in test/blackbox-tests/setup-script.sh that drives the --__complete protocol and filters the Values group, along with cram coverage for empty/prefix/no-match tokens, the outside-workspace case, --build-dir, and --root (via dune promotion apply, since the dune promote alias currently uses Common.No_build.term and so doesn't accept --root).

• Fixes shell completion for dune promote #7254
• changelog

[ElectreAAS]

Tested locally on bash and zsh and it doesn't seem to work, is there some additional setup needed to get this working?

[Alizter]

@ElectreAAS There should be no additional setup needed. The usual setup from #14779 should be enough. For dune promote to give you suggestions however, you will need something to promote. Something like misformatting a file and running dune build @fmt should be enough.

[ElectreAAS]

We tested this today, and a problem that popped up is the following:
dune promote doesn't recognize (and thus complete) all the common flags (whereas dune promotion apply does), which is annoying.
This is more annoying because of a different problem: if the binary called isn't dune (but _boot/dune.exe for us), completion doesn't kick in at all

[ElectreAAS]

dune promote doesn't recognize (and thus complete) all the common flags (whereas dune promotion apply does), which is annoying.

I think I've found the culprit for this: #6160 (comment) :)

[Alizter]

This is more annoying because of a different problem: if the binary called isn't dune (but _boot/dune.exe for us), completion doesn't kick in at all

This one actually has an easy fix on bash:

$ eval "$(_boot/dune.exe completion bash)"
$ complete -F _dune_cmdliner _boot/dune.exe

will allow it to work with any binary name you want. We should document this in the man page and work out what needs to be done for the other shells.

[Alizter]

dune promote doesn't recognize (and thus complete) all the common flags (whereas dune promotion apply does), which is annoying.

I think that the bug is really that dune promotion apply even accepts these flags. It should have the same term as dune promote. However it shouldn't affect this PR.