tests.haskell.ghcWithPackages: init

`ghcWithPackages` broke in #411741, partially because we don't have
tests for it. This adds some tests to make sure it keeps working in the
future. For now these tests will fail until #415436 is fixed.

This is split off of #415434.

Adds a regression test for https://github.com/NixOS/nixpkgs/pull/224542

pkgs/test/haskell/default.nix

@@ -1,10 +1,11 @@
 { lib, callPackage }:
 
 lib.recurseIntoAttrs {
-  shellFor = callPackage ./shellFor { };
   cabalSdist = callPackage ./cabalSdist { };
   documentationTarball = callPackage ./documentationTarball { };
-  setBuildTarget = callPackage ./setBuildTarget { };
+  ghcWithPackages = callPackage ./ghcWithPackages { };
   incremental = callPackage ./incremental { };
+  setBuildTarget = callPackage ./setBuildTarget { };
+  shellFor = callPackage ./shellFor { };
   upstreamStackHpackVersion = callPackage ./upstreamStackHpackVersion { };
 }

pkgs/test/haskell/ghcWithPackages/default.nix

@@ -0,0 +1,48 @@
+{
+  lib,
+  runCommand,
+  haskellPackages,
+}:
+
+lib.recurseIntoAttrs {
+  # This is special-cased to return just `ghc`.
+  trivial = haskellPackages.ghcWithPackages (hsPkgs: [ ]);
+
+  # Here we actually build a trivial package.
+  hello = haskellPackages.ghcWithPackages (hsPkgs: [
+    hsPkgs.hello
+  ]);
+
+  # Here we build a database with multiple packages.
+  multiple = haskellPackages.ghcWithPackages (hsPkgs: [
+    hsPkgs.hspec
+    hsPkgs.unordered-containers
+  ]);
+
+  # See: https://github.com/NixOS/nixpkgs/pull/224542
+  regression-224542 =
+    runCommand "regression-224542"
+      {
+        buildInputs = [
+          (haskellPackages.ghcWithPackages (hsPkgs: [
+            hsPkgs.hspec
+          ]))
+        ];
+      }
+      ''
+        ghc --interactive \
+          -Werror=unrecognised-warning-flags \
+          -Werror=missed-extra-shared-lib \
+          2>&1 \
+        | tee ghc-output.txt
+
+        # If GHC failed to find a shared library, linking dylibs in
+        # `ghcWithPackages` didn't work correctly.
+        if grep --quiet "error: .*-Wmissed-extra-shared-lib" ghc-output.txt \
+          && grep --quiet "no such file" ghc-output.txt; then
+          exit 1
+        fi
+
+        touch $out
+      '';
+}