Stack doesn't rebuild enough when using Custom build-type

[mboes]

Steps to reproduce

Create a trivial stack project with the following Setup.hs (and setting build-type: Custom):

import Distribution.Simple

main = defaultMainWithHooks simpleUserHooks { postBuild = putStrLn "Hey!" }

Then stack build twice.

Expected

stack should run the preBuild/postBuild hooks each time stack build is called. In general these may be callouts to make or any other foreign build system, whose dependency graph is invisible to Cabal/Stack/GHC.

Actual

stack runs these hooks once only, unless Haskell source files change. Note that cabal-install does rerun these hooks every time. It's Stack's recompilation avoidance that seems to be the problem here.

[mboes]

One possible solution here could be to treat build-type: Custom specially, i.e. be less aggressive about recompilation avoidance in that particular case.

[mgsloan]

Yeah, special casing built-type: Custom for this makes sense to me.

[mboes]

Problem is, if package D has build-type: Custom, and the dependency chain in a multi-package project looks like A -> B -> C -> D, then the hooks will be rerun each time for D and presumably A, B, C become out-of-date and rebuild too? Likely no object files will be rebuilt, but the null build may take quite a bit more time.

What about another solution: take into account the extra-source-files field, and posit that build-type: Custom only ever needs to rerun if any of the sources files listed there (+ those files already taken into account) are newer. This is perhaps not correct in general, but should cover nearly every sane use case for using build hooks.

[mgsloan]

Yeah, though it seems to me like a strange behavior to toggle based on build-type. Perhaps changes to extra-source-files should always cause package dirtiness? It's better to have false positives than false negatives for dirtiness checking.

[borsboom]

I think this is resolved by the merge of #2362. Please re-open if not.