`shellFor` apparently broken

[lierdakil]

Describe the bug

What it says in the subject, shellFor is apparently broken.

happy-plan-to-nix-pkgs tries to build happy 1.21.0, which is pretty much unbuildable (by design).

• Build system: x86_64-linux
• GHC version: checked with 9.0.2, 9.2.5, 9.2.7 (i.e. stack lts-19.3, lts-20.4 and lts-20.14, respectively)
• Haskell.nix version: fce554b

Steps To Reproduce

Minimal(-ish) reproducer: https://github.com/lierdakil/haskell-nix-shellFor-repro. Clone and run nix develop .

Expected behavior

Shell starts.

Actual behavior

error: builder for '/nix/store/kkyb143n3pvd1ia991nwmfrxhd469bzx-happy-plan-to-nix-pkgs.drv' failed with exit code 1;
Using index-state 2023-03-16T00:00:00Z
Warning: The package list for 'hackage.haskell.org' is 19432 days old.
Run 'cabal update' to get the latest list of available packages.
Resolving dependencies...
make-install-plan: dieVerbatim: user error (Error: make-install-plan: Could not resolve dependencies:
[__0] next goal: happy (user goal)
[__0] rejecting: happy-1.20.1.1, happy-1.20.0, happy-1.19.12, happy-1.19.11,
happy-1.19.10, happy-1.19.9, happy-1.19.8, happy-1.19.7, happy-1.19.6,
happy-1.19.5, happy-1.19.4, happy-1.19.3, happy-1.19.2, happy-1.19.1,
happy-1.19.0, happy-1.18.11, happy-1.18.10, happy-1.18.9, happy-1.18.8,
happy-1.18.7, happy-1.18.6, happy-1.18.5, happy-1.18.4, happy-1.18.2,
happy-1.18.1, happy-1.18 (constraint from user target requires ==1.21.0)
[__0] trying: happy-1.21.0
[__1] next goal: base (dependency of happy)
[__1] rejecting: base-4.16.4.0/installed-4.16.4.0 (conflict: happy => base<0)
[__1] skipping: base-4.18.0.0, base-4.17.0.0, base-4.16.4.0, base-4.16.3.0,
base-4.16.2.0, base-4.16.1.0, base-4.16.0.0, base-4.15.1.0, base-4.15.0.0,
base-4.14.3.0, base-4.14.2.0, base-4.14.1.0, base-4.14.0.0, base-4.13.0.0,
base-4.12.0.0, base-4.11.1.0, base-4.11.0.0, base-4.10.1.0, base-4.10.0.0,
base-4.9.1.0, base-4.9.0.0, base-4.8.2.0, base-4.8.1.0, base-4.8.0.0,
base-4.7.0.2, base-4.7.0.1, base-4.7.0.0, base-4.6.0.1, base-4.6.0.0,
base-4.5.1.0, base-4.5.0.0, base-4.4.1.0, base-4.4.0.0, base-4.3.1.0,
base-4.3.0.0, base-4.2.0.2, base-4.2.0.1, base-4.2.0.0, base-4.1.0.0,
base-4.0.0.0, base-3.0.3.2, base-3.0.3.1 (has the same characteristics that
caused the previous version to fail: excluded by constraint '<0' from 'happy')
[__1] fail (backjumping, conflict set: base, happy)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: happy, base
)

[lierdakil]

This took a lot of debugging, but apparently you just need to set allToolDeps = false; I believe #1793 #1794 are relevant.

[philderbeast]

Selecting exactDeps = true seems to prevent this problem too:

project.shellFor {
    ...
    # Prevents cabal from choosing alternate plans, so that
    # *all* dependencies are provided by Nix.
    exactDeps = true;
  }

Makes sense after looking at the source because:

haskell.nix/modules/shell.nix

Lines 32 to 41 in 5b1e10c

	allToolDeps = lib.mkOption {
	type = lib.types.bool;
	default = !config.exactDeps;
	description = ''
	Indicates if the shell should include all the tool dependencies
	of in the haskell packages in the project. Defaulted to `false` in
	stack projects (to avoid trying to build the tools used by
	every `stackage` package).
	'';
	};

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.