pkgs.tests.haskell.shellFor: fix test (#392234)

doc/languages-frameworks/haskell.section.md

@@ -619,6 +619,12 @@ environment. This means you can reuse Nix expressions of packages included in
 nixpkgs, but also use local Nix expressions like this: `hpkgs: [
 (hpkgs.callPackage ./my-project.nix { }) ]`.
 
+`extraDependencies`
+: Extra dependencies, in the form of cabal2nix build attributes. An example use
+case is when you have Haskell scripts that use libraries that don't occur in
+your packages' dependencies. Example: `hpkgs: {libraryHaskellDepends =
+[ hpkgs.releaser ]}`. Defaults to `hpkgs: { }`.
+
 `nativeBuildInputs`
 : Expects a list of derivations to add as build tools to the build environment.
 This is the place to add packages like `cabal-install`, `doctest` or `hlint`.

pkgs/test/haskell/shellFor/default.nix

@@ -68,4 +68,8 @@
         maintainers = allMaintainers;
         inherit (cabal-install.meta) platforms;
       };
+    # `shellFor` adds a `buildCommand` (via `envFunc -> runCommandCC`), which
+    # overrides custom phases. To ensure this test's phases run, we remove
+    # that `buildCommand` from the derivation.
+    buildCommand = null;
   })