Cabal tries to rebuild build-tool-depends in Nix shells where they are already provided

[lf-]

Describe the bug

When I invoke cabal test, cabal tries to build hspec-discover. This is deeply mysterious to me, since it is listed in ghc-pkg dump | rg -C10 hspec-discover on account of Nix putting it there.

I think a possible cause is that that's just the library and not the executable, but the Nix infrastructure will dump the executable into the PATH if it's in build-tool-depends (cabal2nix will ensure this).

So I'm filing this bug because this means I can either have build-tools and have it do pointless work in a Nix shell (but notably not when Nix invokes the testsuite as part of a build, since it invokes it with ./Setup test), or have the build of tests fail outside a Nix shell.

To Reproduce

Clone https://github.com/lf-/cabal-build-tools-repro

co/cabal-repro - [main] » nix develop --extra-experimental-features "flakes nix-command" -c cabal v2-test  
warning: Using saved setting for 'allow-import-from-derivation = true' from ~/.local/share/nix/trusted-settings.json.
Resolving dependencies...
Build profile: -w ghc-9.2.4 -O1
In order, the following will be built (use -v for more details):
 - hspec-discover-2.10.6 (lib) (requires build)
 - hspec-discover-2.10.6 (exe:hspec-discover) (requires build)
 - sample-0.0.0 (test:test) (first run)
Starting     hspec-discover-2.10.6 (lib)
^C

Expected behavior

Cabal should not bother building hspec-discover since it exists in PATH due to Nix (I think it's possibly reason able to ignore the one on PATH if Nix wasn't what put it there).

System information

• Operating system: archlinux with nix
  GHC version: 9.2.4
  Cabal version:

[jade@tail-bot cabal-repro]$ cabal --version
cabal-install version 3.6.2.0
compiled using version 3.6.3.0 of the Cabal library 

Additional context
Add any other context about the problem here.

[lf-]

cc @parsonsmatt since you hit this the other day also

[parsonsmatt]

#8434 is a related issue

[fgaz]

This is basically #8434 (cabal-install can't know that the installed package is the required version), let's keep the discussion there