Backtrack when no pkgconfigdb is present

[gbaz]

Potentially resolves #7448

This is a one lexeme change that I would argue "fixes" pkgconfig-depends handling in the solver. Before, if there was no pkg-config that could be found, the solver would optimistically succeed. But since the builder then requires using pkg-config to get the linking flags, this would necessarily fail on build anyway. Now, we fail. This lets a user set up an auto flag that toggles between using a pkgconfig-depends and explicit extra-libraries etc stanza.

I think this gives a nice solution that is strictly better than the prior situation.

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

[Mikolaj]

Another one-liner that solves world peace? Sounds legit. :D

But seriously, this could work. Any chance for a test and changelog?

[gbaz]

Changelog, sure. I'm not quite sure how one might add a test for something like this, since it explicitly involves pkg-config not being on the path, etc. Advice in that direction is appreciated.

[sebright]

I'm not quite sure how one might add a test for something like this, since it explicitly involves pkg-config not being on the path, etc.

You could add unit tests for solving without pkg-config, similar to the existing pkg-config tests:

cabal/cabal-install/tests/UnitTests/Distribution/Solver/Modular/Solver.hs

Lines 255 to 260 in 55c426f

	, testGroup "Pkg-config dependencies" [
	runTest $ mkTestPCDepends [] dbPC1 "noPkgs" ["A"] anySolverFailure
	, runTest $ mkTestPCDepends [("pkgA", "0")] dbPC1 "tooOld" ["A"] anySolverFailure
	, runTest $ mkTestPCDepends [("pkgA", "1.0.0"), ("pkgB", "1.0.0")] dbPC1 "pruneNotFound" ["C"] (solverSuccess [("A", 1), ("B", 1), ("C", 1)])
	, runTest $ mkTestPCDepends [("pkgA", "1.0.0"), ("pkgB", "2.0.0")] dbPC1 "chooseNewest" ["C"] (solverSuccess [("A", 1), ("B", 2), ("C", 1)])
	]

It looks like all of the tests create a pkg-config DB by calling pkgConfigDbFromList , so you would need to add an option for no DB:

cabal/cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL/TestCaseUtils.hs

Line 222 in 55c426f

, testPkgConfigDb = pkgConfigDbFromList pkgConfigDb

[gbaz]

Thanks! I implemented tests as suggested

[sebright]

I think it would be useful to also keep the empty pkg-config test case, using Just [].

[fgaz]

• The documentation has been updated, if necessary.

👀