Building the defaultSetup against the wrong lib:Cabal

[angerman]

To build components we build the Setup module, which links against lib:Cabal, the code for doing this is in

haskell.nix/builder/hspkg-builder.nix

Lines 33 to 52 in 19a1220

	defaultSetupSrc = builtins.toFile "Setup.hs" ''
	import Distribution.Simple
	main = defaultMain
	'';
	defaultSetup = buildPackages.runCommand "default-Setup" { nativeBuildInputs = [(ghc.passthru.buildGHC or ghc)]; } ''
	cat ${defaultSetupSrc} > Setup.hs
	mkdir -p $out/bin
	${(ghc.passthru.buildGHC or ghc).targetPrefix}ghc Setup.hs --make -o $out/bin/Setup
	'';
	setup = if package.buildType == "Simple" && package.setup-depends == []
	then defaultSetup
	else setup-builder {
	component = components.setup // {
	depends = components.setup.depends ++ package.setup-depends;
	extraSrcFiles = components.setup.extraSrcFiles ++ [ "Setup.hs" "Setup.lhs" ];
	};
	inherit package name src flags revision patches defaultSetupSrc;
	inherit (config) preUnpack postUnpack;
	};

We thus build Setup against the lib:Cabal that comes with ghc, which we try to patch across all ghc installs:

haskell.nix/overlays/patches/ghc/ghc-8.6-Cabal-fix-datadir.patch

Lines 1 to 21 in 19a1220

	Submodule libraries/Cabal contains modified content
	diff --git a/libraries/Cabal/Cabal/Distribution/Simple/Build/PathsModule.hs b/libraries/Cabal/Cabal/Distribution/Simple/Build/PathsModule.hs
	index 678ccbca3..ffa712e8a 100644
	--- a/libraries/Cabal/Cabal/Distribution/Simple/Build/PathsModule.hs
	+++ b/libraries/Cabal/Cabal/Distribution/Simple/Build/PathsModule.hs
	@@ -192,10 +192,14 @@ generate pkg_descr lbi clbi =
	bindir = flat_bindir,
	libdir = flat_libdir,
	dynlibdir = flat_dynlibdir,
	- datadir = flat_datadir,
	libexecdir = flat_libexecdir,
	sysconfdir = flat_sysconfdir
	} = absoluteComponentInstallDirs pkg_descr lbi cid NoCopyDest
	+
	+ InstallDirs {
	+ datadir = flat_datadir
	+ } = absoluteInstallDirs pkg_descr lbi NoCopyDest
	+
	InstallDirs {
	bindir = flat_bindirrel,
	libdir = flat_libdirrel,

As it so happens our bootstrap compiler are not patched but might still exhibit faulty lib:Cabals. As such it seems only prudent that we would link the defaultSetup against a controlled lib:Cabal as well.

I believe all we'd need to do is to use the setup-builder instead and feed it the correct depends value.

[michaelpj]

This would also be useful where you need a newer version of cabal to build a package, sometimes there are bugs.

[michaelpj]

e.g. I wanted to pass --program-suffix to $SETUP build, but this is only supported in newer versions of cabal.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[hamishmack]

The haskell.nix default setup is now built with the Cabal version based on what cabal-install haskell.nix uses (cabal-install version used the latest version based on the internal index state).