[nix-local-build] Doesn't reconfigure after a custom Setup rebuilds

[ezyang]

What is says on the tin.

[ezyang]

As a workaround, if you delete dist-newstyle/build/Cabal-1.23.0.0/cache/config (or whatever your package is) that will induce a reconfigure.

[dcoutts]

We need to track the files of the custom setup.

[nh2]

We're hitting a similar issue:

cabal v2-build does not notice when PKG_CONFIG_PATH changes.

It just skips over running pkg-config in that case, when I'd expect it should probably be re-run.

Workaround:

rm dist/build/cache/*-plan

Some notes I wrote about it:

• pkg-config is invoked by cabal not during v2-configure but during v2-build
  • at least for our build, unclear if that's always this way or only because we use a custom Setup.hs with build-type: Custom
• but if you change PKG_CONFIG_PATH, none of v2-configure + v2-build re-run pkg-config
  • v2-configure seems unnecessary, v2-build seems to include that; but v2-repl does not, which is confusing
  • v2-build --only-configure does the pkg-config steps at the very beginning, but also caches them on re-run
  • we found that we can force it to be re-run of pkg-config by rm dist/build/cache/*-plan