Find and run cabal in user original $PATH

[jneira]

• We've found that the cabalexecutable used within stack install.hs executions after a first stack install.hs stack-install-cabal is the cached in $STACK_ROOT/snapshots/{hash}/bin. The cause is stack prepends that directory to the $PATH environment variable. That supposes:
  • If you delete the cabal executable in $PATH after running stack install.hs stack-install-cabal, another invocation doesn't copy again the cabal executable, cause the version cached by stack is found. (thanks @jchia for detected it)
  • All stack install.hs cabal-* use that cached version and no the original one, so if you upgrade your cabal in $PATH to 3.0.0.0 stack will continue using its cached version, (currently 2.4.1.0)
    • So in windows you could not use those goals

To avoid it i had to remove manually $STACK_ROOT/snapshots/{hash}/bin from $PATH, an ugly ugly hack, but i didint find better way to do it (via stack flags or alternative env vars)

I think this one would fix haskell/vscode-haskell#131

[samuelpilz]

I like the idea, but the approach is very hacky indeed.

Is it a possible alternative to use findExecutables and select the appropriate executable from that list?

[jneira]

I thought in use that at first but unfortunately in windows findExecutables only returns the first one (as it states in the comments).

Imho the right one would be to have in stack a way (flag or whatever) to ignore its modifications over the $PATH variable... 😟

[samuelpilz]

If there is no better cross platform solution, this PR is fine

[alanz]

I am having issues on Debian with tests failing when I build locally, but passing fine on CI, e.g. https://circleci.com/workflow-run/57c08f4c-eca4-46af-bedd-97c3ae0d0835.

I wonder if this cached cabal could be the issue for me.

[jneira]

i've opened an issue in stack to try to remove or make less britle the hack: commercialhaskell/stack#5055

[jneira]

I've updated the pr:

• change the hack function name to withoutStackCachedBinaries: an ugly hack deserves a precise name
• Remove just ${snapshot-install-root}/bin and ${local-install-root}\bin

This could be merged, as the stack issue has not feedback and there is no better alternative

[samuelpilz]

Im ok with this. @fendor should we merge this now?