Merged plugins pull in disabled deps when building with `Setup.hs`

[hololeap]

I'm taking a look at packaging haskell-language-server-2.7.0.0 for Gentoo Linux. Currently, I have 2.6.0.0 and most plugins installed to my system, although I do not have the hls-fourmolu-plugin or fourmolu packages installed. Just experimenting with the Setup.hs interface, I notice that the fourmolu dependency is being pulled in even when the fourmolu flag is disabled:

cd haskell-language-server-2.7.0.0/
runhaskell Setup.hs configure --flag=-fourmolu

As you can see, it is still looking for fourmolu:

Configuring haskell-language-server-2.7.0.0...
Setup.hs: Encountered missing or private dependencies:
fourmolu >=0.14 && <0.16,
ghcide ==2.7.0.0,
hiedb >=0.6.0.0 && <0.7,
hls-graph ==2.7.0.0,
hls-plugin-api ==2.7.0.0,
lsp >=2.4 && <2.5

The changes made in #3976 seem to be selectively choosing which sub-libraries to build using build-depends:

haskell-language-server/haskell-language-server.cabal

Lines 1298 to 1301 in 41de40e

	common fourmolu
	if flag(fourmolu)
	build-depends: haskell-language-server:hls-fourmolu-plugin
	cpp-options: -Dhls_fourmolu

It seems to me that Setup.hs does not seem to have the functionality to handle this, and instead tries to build all sub-libraries mentioned in the .cabal file, regardless of what flags are toggled.

This experiment was done using ghc-9.2.8 and Cabal-3.6.3.0.

[michaelpj]

I am pretty sure the Setup.hs should have the ability to build individual components correctly. haskell.nix uses it fine. I note that I get all sorts of weird errors from running just runhaskell Setup.hs configure, so I wonder if that simply isn't the right way to use it?

[michaelpj]

You might need to pass a target? runhaskell Setup.hs configure exe:haskell-language-server --flags=-fourmolu?

[hololeap]

Thank you!