haskellPackages.gitit: unbreak

pandoc 2.12 changed and removed a few exports gitit used. I procured a
patch which fixes those without any refactoring by vendoring in the
removed function from pandoc which is no problem as they are both
available under the GPL 2.0.

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

@@ -1165,10 +1165,11 @@ self: super: {
   # $HOME, which we don't have in our build sandbox.
   cabal-install-parsers = dontCheck super.cabal-install-parsers;
 
-  # version constraints break the build, so we jailbreak
-  # can be removed at a new release which also fixes
-  # https://github.com/jgm/gitit/issues/665
-  gitit = doJailbreak super.gitit;
+  # * jailbreak can be removed at the next release (current is 0.13.0.0)
+  # * patch fixes compilation with pandoc >= 2.12, can be removed if a
+  #   release contains https://github.com/jgm/gitit/pull/670 or equivalent.
+  #   Patch is vendored in as it may change upstream in the future.
+  gitit = doJailbreak (appendPatch super.gitit ./patches/gitit-pandoc-2.12.patch);
 
   # Test suite requires database
   persistent-mysql = dontCheck super.persistent-mysql;

pkgs/development/haskell-modules/patches/gitit-pandoc-2.12.patch

@@ -0,0 +1,65 @@
+commit a03d3b043458f45d29ba32068a77c0d3b8a4223f
+Author: sternenseemann <0rpkxez4ksa01gb3typccl0i@systemli.org>
+Date:   Fri Apr 2 15:14:02 2021 +0200
+
+    Allow compilation with pandoc 2.12 and 2.13
+    
+    pandoc 2.13 introduced the following breakages for gitit:
+    
+    * UTF8.readFile now returns a Text which is actually ideal for gitit.
+      If pandoc is new enough we just make readFileUTF8 an alias for
+      UTF8.readFile.
+    
+    * Text.Pandoc.Shared no longer exports substitute. In order to be
+      conservative I've chosen to just copy the substitute function from
+      pandoc 2.11.4. I need this patch kind of urgently so I didn't want to
+      make any changes or refactors independently from upstream if
+      avoidable. However, I'd be happy to rebase this PR branch to adopt a
+      different solution to just copying the function.
+
+diff --git a/src/Network/Gitit/Authentication.hs b/src/Network/Gitit/Authentication.hs
+index 4c240e7..c0f92fd 100644
+--- a/src/Network/Gitit/Authentication.hs
++++ b/src/Network/Gitit/Authentication.hs
+@@ -44,7 +44,7 @@ import System.Exit
+ import System.Log.Logger (logM, Priority(..))
+ import Data.Char (isAlphaNum, isAlpha)
+ import qualified Data.Map as M
+-import Text.Pandoc.Shared (substitute)
++import Data.List (stripPrefix)
+ import Data.Maybe (isJust, fromJust, isNothing, fromMaybe)
+ import Network.URL (exportURL, add_param, importURL)
+ import Network.BSD (getHostName)
+@@ -54,6 +54,16 @@ import Codec.Binary.UTF8.String (encodeString)
+ import Data.ByteString.UTF8 (toString)
+ import Network.Gitit.Rpxnow as R
+ 
++-- | Replace each occurrence of one sublist in a list with another.
++--   Vendored in from pandoc 2.11.4 as 2.12 removed this function.
++substitute :: (Eq a) => [a] -> [a] -> [a] -> [a]
++substitute _ _ [] = []
++substitute [] _ xs = xs
++substitute target replacement lst@(x:xs) =
++    case stripPrefix target lst of
++      Just lst' -> replacement ++ substitute target replacement lst'
++      Nothing   -> x : substitute target replacement xs
++
+ data ValidationType = Register
+                     | ResetPassword
+                     deriving (Show,Read)
+diff --git a/src/Network/Gitit/Util.hs b/src/Network/Gitit/Util.hs
+index c5e9fe5..067130a 100644
+--- a/src/Network/Gitit/Util.hs
++++ b/src/Network/Gitit/Util.hs
+@@ -45,7 +45,11 @@ import Network.URL (encString)
+ 
+ -- | Read file as UTF-8 string.  Encode filename as UTF-8.
+ readFileUTF8 :: FilePath -> IO Text
++#if MIN_VERSION_pandoc(2,12,0)
++readFileUTF8 = UTF8.readFile
++#else
+ readFileUTF8 = fmap T.pack . UTF8.readFile
++#endif
+ 
+ -- | Perform a function a directory and return to working directory.
+ inDir :: FilePath -> IO a -> IO a