haskellPackages.hnix: unbreak

The mystery build failure was caused by having the same instance as an
orphan and imported from ref-tf 0.5 (why ever that doesn't warrant a
logged error message…). The solution for this is
https://github.com/haskell-nix/hnix/pull/918, which sadly doesn't apply
cleanly on the hnix 0.12.0.1 tarball. Therefore I've backported the
patch until hnix hopefully gets a new hackage release soon.

pkgs/development/haskell-modules/configuration-common.nix

@@ -197,7 +197,19 @@ self: super: {
   digit = doJailbreak super.digit;
 
   # 2020-06-05: HACK: does not pass own build suite - `dontCheck`
-  hnix = generateOptparseApplicativeCompletion "hnix" (dontCheck super.hnix);
+  hnix = generateOptparseApplicativeCompletion "hnix"
+    (overrideCabal super.hnix (drv: {
+      doCheck = false;
+      prePatch = ''
+        # fix encoding problems when patching
+        ${pkgs.dos2unix}/bin/dos2unix hnix.cabal
+      '' + (drv.prePatch or "");
+      patches = [
+        # support ref-tf in hnix 0.12.0.1, can be removed after
+        # https://github.com/haskell-nix/hnix/pull/918
+        ./patches/hnix-ref-tf-0.5-support.patch
+      ] ++ (drv.patches or []);
+    }));
 
   # Fails for non-obvious reasons while attempting to use doctest.
   search = dontCheck super.search;

pkgs/development/haskell-modules/patches/hnix-ref-tf-0.5-support.patch

@@ -0,0 +1,34 @@
+diff '--color=auto' '--color=never' -r --unified hnix-0.12.0.1/hnix.cabal hnix-patched/hnix.cabal
+--- hnix-0.12.0.1/hnix.cabal	2001-09-09 03:46:40.000000000 +0200
++++ hnix-patched/hnix.cabal	2021-05-05 12:07:38.388267353 +0200
+@@ -430,7 +430,7 @@
+     , parser-combinators >= 1.0.1 && < 1.3
+     , prettyprinter >= 1.7.0 && < 1.8
+     , process >= 1.6.3 && < 1.7
+-    , ref-tf >= 0.4.0 && < 0.5
++    , ref-tf >= 0.5
+     , regex-tdfa >= 1.2.3 && < 1.4
+     , scientific >= 0.3.6 && < 0.4
+     , semialign >= 1 && < 1.2
+diff '--color=auto' '--color=never' -r --unified hnix-0.12.0.1/src/Nix/Fresh.hs hnix-patched/src/Nix/Fresh.hs
+--- hnix-0.12.0.1/src/Nix/Fresh.hs	2001-09-09 03:46:40.000000000 +0200
++++ hnix-patched/src/Nix/Fresh.hs	2021-05-05 12:07:45.841267497 +0200
+@@ -65,18 +65,3 @@
+ 
+ runFreshIdT :: Functor m => Var m i -> FreshIdT i m a -> m a
+ runFreshIdT i m = runReaderT (unFreshIdT m) i
+-
+--- Orphan instance needed by Infer.hs and Lint.hs
+-
+--- Since there's no forking, it's automatically atomic.
+-instance MonadAtomicRef (ST s) where
+-  atomicModifyRef r f = do
+-    v <- readRef r
+-    let (a, b) = f v
+-    writeRef r a
+-    return b
+-  atomicModifyRef' r f = do
+-    v <- readRef r
+-    let (a, b) = f v
+-    writeRef r $! a
+-    return b