cabal init -n fails with opaque error message when git not installed

[jnhnum1]

On a new machine with Cabal 3.8.1.0, I tried running
cabal init -n newapp
and got what appeared to be an uncaught exception:
git: readCreateProcessWithExitCode: posix_spawnp: does not exist (No such file or directory)
It took a little while to figure out, but the issue seems to be that I didn't have git installed.
Perhaps this case could be handled with a more helpful error message.

[ulysses4ever]

Relevant code:

cabal/cabal-install/src/Distribution/Client/Init/NonInteractive/Heuristics.hs

Lines 178 to 186 in 55b4ed9

	guessGitInfo :: Interactive m => String -> m String
	guessGitInfo target = do
	info <- readProcessWithExitCode "git" ["config", "--local", target] ""
	if null $ snd' info
	then trim . snd' <$> readProcessWithExitCode "git" ["config", "--global", target] ""
	else return . trim $ snd' info
	where
	snd' (_, x, _) = x

Should be easy to fix. Anyone?

[gbaz]

@ptkato care to make a patch?

[BasLaa]

Should an error be thrown if git is not installed in this case? Then perhaps something like this would work:
Then you could check something like if fst' info /= ExitSuccess then ... on the second readProcessWithExitCode call with the --global flag?

[ptkato]

git is needed to retrieve the user name and user email information for the cabal file. Now, it's the most reliable way of getting such info for the non-interactive workflow. I'm torn if we should throw an error or not, I don't recall if such user info is mandatory, even if it is, I think an error would be out of proportion (what if the user doesn't want git installed?); we could instead throw a warning to make the user aware that the name and email could not be retrieved instead.

[ulysses4ever]

We definitely don't want to fail (in any way) if git is not installed. A warning, perhaps, could be added, but I'm not big on that either: I think a warning is justified when something could go wrong, and it's not the case here.

[BasLaa]

Perhaps simply an empty default value for user name and user email when git is not installed with a note instead of a warning?

[ptkato]

Yes, sorry, by warning I didn't really mean "warning", but what @BasLaa suggested instead.

[ulysses4ever]

No, you’re good. I’m just thinking aloud.

Empty default is fine. For the “note” idea: I’d be curious to see a sketch, but I’m open minded.

[BasLaa]

I can give it a try this weekend.