JS Template Haskell hackage dependency splicing failure

[ymeister]

Describe the bug

When cross-compiling to JS a hackage dependency which involves actual template haskell splicing and not just declaration of template haskell functions you get an error:

    JS interpreter: couldn't find "ghci" package

Obvious solution does not fix it:

if arch(javascript)
  extra-packages: ghci

• Build system: x86_64-linux
• GHC version: 9.12.2
• Haskell.nix version (or commit) used: e567ebc (tag: 2025.08.03)

Steps To Reproduce

1. Add th-orphans to build-depends of https://github.com/input-output-hk/haskell.nix/blob/master/test/js-template-haskell/js-template-haskell.cabal
2. Run the build: nix-build -A allJobs.x86_64-linux.unstable.ghc9122.ghcjs.tests.js-template-haskell.build

Expected behavior

Successful compilation.

Additional context

1. This is a regression, as last I tried using extra-packages: ghci on ghc910 it solved the problem. Now it doesn't. I assume this PR might be related to this Fix cabal install in the presence of extra-packages (backport #9719) haskell/cabal#9875.
2. My second assumption was that it maybe somehow related to this Fix -inplace issue with ghc 9.8.1 boot packages #2161. I.e. when ghc tries to pick ghci, while it should have picked ghci-inplace. Honestly doubt that's the case, but still leaving it here for the full picture.

Hotfix:

modules = [
  ({ config, ... }: {
    configureFlags = [ "--package-db ${config.ghc.package.outPath}/${config.ghc.package.libDir}/package.conf.d" ];
  })
];

This places all installed ghc libraries, ghci in particular, in scope of all packages. Might be an overkill, but at least it works.

[stale]

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