add dune show command (or rename dune describe?)

[Alizter]

We should add a dune show command that will collect together many subcommands whose jobs it is to show some information about the workspace. This should make these commands easier to use and clear up the toplevel cli.

• dune show targets feature: dune show targets and dune show aliases #7770
• dune show aliases feature: dune show targets and dune show aliases #7770
• dune show rules (should take over dune rules) show: print_rules now part of show command #8000
• dune show env (should take over dune printenv) feature: add dune show env and make dune printenv an alias of it #7985
• migration from dune describe, create dune show command group #7946
  • dune show opam-files
  • dune show pp
  • dune show external-lib-deps
  • dune show workspace
• dune show installed-libraries show: add Installed_libraries to show #8135
• dune show targets (--all) feature: --all option for dune show targets #8167

Maybe the best way to go about this is to extend dune describe and rename it to dune show. Keeping it around as a command alias seems sensible. dune describe also needs to be converted to command groups.

[nojb]

Also: dune installed-libraries should probably become dune show installed-libraries.

For dune describe there are a number of subcommands: dune describe opam-files, dune describe pp and dune describe external-lib-deps. They should all be migrated under the dune show command.

[Alizter]

@snowleopard What exactly do you want dune show sources to do?

[snowleopard]

@snowleopard What exactly do you want dune show sources to do?

Right now, if a directory contains an ignored file, a source file, and a target (generated) file, dune show targets would print the source and the target files.

I think there are possibly two issues with it.

Firstly, seeing the source file in the output may be confusing: the user asked for "targets", after all.

Secondly, there is currently no way to see just sources (still skipping ignored files and targets) or just targets (skipping ignored files and sources).

I don't necessarily advocate for adding a new command, but the current design doesn't seem great.

[snowleopard]

Here is an alternative design that may be an improvement:

• Change the command to dune show files to avoid confusion. Also works well with a possible dune show dirs we could add in future.
• Support flags dune show files --sources-only and --targets-only to make it possible to see the corresponding subsets.

[Alizter]

I don't like the dune show files idea. We are declaring every buildable target to the user, this includes the source files. I would rather have an option to exclude source files such as dune show targets --no-sources. Also dune show sources seems kind of moot as this is essentially just ls at this point.

[snowleopard]

We are declaring every buildable target to the user, this includes the source files.

Are you sure the majority of Dune users considers sources to be targets? I doubt it. Perhaps we can ask them!

That Dune copies sources into _build, and therefore happens to have build rules for them, seems somewhat accidental to me/leaking implementation details.

Also dune show sources seems kind of moot as this is essentially just ls at this point.

Build systems (Dune including) have non-trivial logic for ignoring some source files. Having a tool to expose this behaviour can be valuable for debugging; ls won't help you there.