refactor(3p/overlays): Move haskell overlay to new tree location

nixpkgs_exposed is going away, and the haskell overlay is independent
from that.

See also b/108, cl/2910

Change-Id: I3aea6dfc427a914f3f88146fd0b45d60dfd45a1a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2918
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

third_party/overlays/haskell/default.nix

@@ -0,0 +1,34 @@
+# Defines overrides for Haskell packages, for example to avoid
+# breakage currently present in nixpkgs or to modify package versions.
+
+{ ... }: # This file needs nothing from readTree
+{ pkgs }: # ... but is called with a separate package set in the overlay
+
+self: super: with pkgs.haskell.lib; rec {
+  generic-arbitrary = appendPatch
+    super.generic-arbitrary
+    [ ./patches/generic-arbitrary-export-garbitrary.patch ];
+
+  random = dontCheck (self.callHackageDirect {
+    pkg = "random";
+    ver = "1.2.0";
+    sha256 = "06s3mmqbsfwv09j2s45qnd66nrxfp9280gnl9ng8yh128pfr7bjh";
+  } {});
+
+  # random <1.2
+  test-framework = doJailbreak super.test-framework;
+  hashable = doJailbreak super.hashable;
+  test-framework-quickcheck2 = doJailbreak super.test-framework-quickcheck2;
+
+  # can be removed if we have the following PR or equivalent
+  # https://github.com/NixOS/nixpkgs/pull/116931
+  hedgehog-classes = overrideCabal super.hedgehog-classes (attrs: {
+    # remove version bound on semirings which is inside a
+    # conditional, so doJailbreak doesn't work
+    prePatch = ''
+      sed -i 's|semirings.*0.6|semirings|g' hedgehog-classes.cabal
+    '';
+  });
+
+  hgeometry-combinatorial = dontCheck super.hgeometry-combinatorial;
+}

third_party/overlays/haskell/patches/generic-arbitrary-export-garbitrary.patch

@@ -0,0 +1,12 @@
+diff --git a/src/Test/QuickCheck/Arbitrary/Generic.hs b/src/Test/QuickCheck/Arbitrary/Generic.hs
+index fed6ab3..91f59f1 100644
+--- a/src/Test/QuickCheck/Arbitrary/Generic.hs
++++ b/src/Test/QuickCheck/Arbitrary/Generic.hs
+@@ -23,6 +23,7 @@ The generated 'arbitrary' method is equivalent to
+ 
+ module Test.QuickCheck.Arbitrary.Generic
+   ( Arbitrary(..)
++  , GArbitrary
+   , genericArbitrary
+   , genericShrink
+   ) where