Make enable/disable nix flag easier to read

[cbclemmer]

This PR is attempting to close #8036

The boolOpt function will not allow for more than one description so I changed the option type from option to multiOption so that the "nix" (--enable-nix and --disable-nix) flags would still be grouped together and allow separate descriptions for disabled and enabled.

As far as the language goes I felt like if the description of "Nix integration" for the --disable-nix was taken out it would make it more clear. It is defined in --enable-nix and --disable-nix is right under it.

---

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• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
• The documentation has been updated, if necessary.

Please also shortly describe how you tested your change. Bonus points for added tests!

[Mikolaj]

Make sense. Would you add a tiny changelog file and test?

[Mikolaj]

@jwaldmann: could you review, please?

[jwaldmann]

I'll look into it, but I'm busy this week.

[Mikolaj]

Thank you. No rush.

[cbclemmer]

@Mikolaj I have tested the --help flag. I assume that when you run cabal foo --enable-nix you would get some kind of error asking for a "shell.nix" file, but I can't get it to change anything on my pc's version of cabal or on my current source build.

[jneira]

hmm, --enable-nix is a global flag and they should go before any command, so cabal --enable-nix build should work:

> cabal help

Command line interface to the Haskell Cabal infrastructure.

See http://www.haskell.org/cabal/ for more information.

Usage: cabal.exe [GLOBAL FLAGS] [COMMAND [FLAGS]]

.....

Global flags:
.....
 --enable-nix                   Enable Nix integration: run commands through
                                nix-shell if a 'shell.nix' file exists
 --disable-nix                  Disable Nix integration: run commands through
                                nix-shell if a 'shell.nix' file exists
....

[cbclemmer]

@jneira Thanks for the suggestion, I tried that and it doesn't give any more info than it did before (I assume it would throw an error if it didn't find "shell.nix" or "default.nix") but it may be working. I've been trying to go through the command with cabal repl to see if the flag is being set correctly in memory but I'm still new to this repo and it's slow going. Give me a day or so to go through it and write a test.

[jneira]

well --enable-nix is not applied to v2- commands (and default build is v2-build) so it will be honoured only for cabal --enable-nix v1-build
see #6444 and #4646

[jneira]

lgtm, thanks for adding a test and the changelog

[Mikolaj]

You could probably obtain the test quicker by copy-pasting something that depends on an existing harness. but test variety is a boon (except when maintaining tests) and this one is really good.

[cbclemmer]

@Mikolaj Thanks, I wasn't sure where to put the test but it seems like that was good enough. I couldn't find anything that was already in place that tested flags so I just set it up with the functions I could find.