cabal new-build doesn't produce logs for local packages

[bgamari]

As far as I can tell cabal new-build no longer produces log files for local package builds. For instance,

$ git clone https://github.com/haskell-hvr/cabal-plan
$ cd cabal-plan
$ cabal new-build all
$ find -iname '*.log' | wc -l 
0

Moreover, -v2 shows no indication that a log was generated. I have a vague sense that this used to work so I suspect there is a regression here.

[ulysses4ever]

Was cabal new-build supposed to generate a log with no explicit request for it? I tried versions back to 2.0 and didn't see it producing any logs on its own, so I'm curious what kind lf logs @bgamari meant and which verision of cabal-install produced those.

If anything, I'd expect v2-build to produce logs if the --build-log flag is triggered. Alas, the same experiment (cabal-install 3 as well as 2) don't produce anything even with the flag. This sounds like a bug as mentioned in #6811. I'm not sure if this is the same bug (and one of these issues should be closed as a dup) or not.

Grepping for --build-log returns a curious result:

cabal/cabal-install/src/Distribution/Client/Setup.hs

Lines 1889 to 1891 in 8248c3d

	, option [] ["build-log"]
	"Log all builds to file (name template can use $pkgid, $compiler, $os, $arch)"
	installLogFile (\v flags -> flags { installLogFile = v })

So, the CLI flag triggers an InstallFlag called installLogFile. It was commited 14 years back here: 5702472 and was supposed for cabal install. And today it's essentially used only in Distribution/Client/Install.hs. No wonder, it has no impact on v2-build.

Arguably, the bug here is that --build-log is shown in cabal v2-build --help: it probably shouldn't (with the current design). Having logs for v2-build would be a feature request.

[mouse07410]

Could you tell me what are my options for getting verbose build log from Cabal (building local packages)?

[ulysses4ever]

@mouse07410 the only workaround I’m aware about is to redirect cabal build’s stdout (and maybe stderr) to a file. Let me know if this is not good enough. This bug (or rather omission in v2) is rather unfortunate, I agree. We’d love to have someone fix it and happy to advise.

[mouse07410]

Well, it's not a beautiful workaround - but it works.

[andreabedini]

This should be easy to fix. All the changes should be contained in buildInplaceUnpackedPackage (to be compared with buildAndInstallUnpackedPackage). One decision to be made would be where to to store them; if we don't already have a good spot in distDirLayout I think we can make a new one?