Allow building with Stackage LTS-21

Only required loosening a bunch of bounds and the following conditional
code changes:

* The API of guessTarget changed, accepting an optional UnitId which we
  can't provide.

* pandoc-3.0 renamed the writeDocbook5 function.

For nix users we need to provide pkg-config to build digest now.

gitit.cabal

@@ -133,8 +133,8 @@ Library
                      mtl,
                      old-time,
                      temporary,
-                     pandoc >= 2.9 && < 2.20,
-                     pandoc-types >= 1.20 && < 1.23,
+                     pandoc >= 2.9 && < 2.20 || >= 3.0 && < 3.2,
+                     pandoc-types >= 1.20 && < 1.24,
                      skylighting >= 0.8.2.3 && < 0.14,
                      bytestring,
                      text,
@@ -149,7 +149,7 @@ Library
                      filestore >= 0.6.5 && < 0.7,
                      zlib >= 0.5 && < 0.7,
                      url >= 2.1,
-                     happstack-server >= 7.5 && < 7.8,
+                     happstack-server >= 7.5 && < 7.9,
                      base64-bytestring >= 0.1,
                      xml >= 1.3.5,
                      hslogger >= 1,
@@ -162,11 +162,11 @@ Library
                      json >= 0.4 && < 0.11,
                      uri-bytestring >= 0.2.3.3,
                      split,
-                     hoauth2 >= 2.3.0 && < 2.7,
+                     hoauth2 >= 2.3.0 && < 2.9,
                      xml-conduit >= 1.5 && < 1.10,
                      http-conduit >= 2.1.6 && < 2.4,
                      http-client-tls >= 0.2.2 && < 0.4,
-                     aeson >= 0.7 && < 2.1,
+                     aeson >= 0.7 && < 2.2,
                      uuid >= 1.3 && < 1.4,
                      network-uri >= 2.6,
                      network >= 2.6 && < 3.2,

src/Network/Gitit/Initialize.hs

@@ -138,7 +138,11 @@ createDefaultPages conf = do
                        RST        -> writeRST defOpts <=< toPandoc
                        Textile    -> writeTextile defOpts <=< toPandoc
                        Org        -> writeOrg defOpts <=< toPandoc
+#if MIN_VERSION_pandoc(3,0,0)
+                       DocBook    -> writeDocBook5 defOpts <=< toPandoc
+#else
                        DocBook    -> writeDocbook5 defOpts <=< toPandoc
+#endif
                        MediaWiki  -> writeMediaWiki defOpts <=< toPandoc
                        CommonMark -> writeCommonMark defOpts <=< toPandoc
 

src/Network/Gitit/Plugins.hs

@@ -41,7 +41,11 @@ loadPlugin pluginName = do
     -- initDynFlags
     unless ("Network.Gitit.Plugin." `isPrefixOf` pluginName)
       $ do
+#if __GLASGOW_HASKELL__ >= 904
+          addTarget =<< guessTarget pluginName Nothing Nothing
+#else
           addTarget =<< guessTarget pluginName Nothing
+#endif
           r <- load LoadAllTargets
           case r of
             Failed -> error $ "Error loading plugin: " ++ pluginName

stack.yaml

@@ -1,6 +1,6 @@
 nix:
   enable: false
-  packages: [zlib zlib.dev]
+  packages: [zlib zlib.dev pkg-config]
 
 flags:
   pandoc:
@@ -18,6 +18,4 @@ extra-deps:
 - filestore-0.6.5
 - recaptcha-0.1.0.4
 
-resolver: lts-20.8
-nix:
-  packages: [zlib]
+resolver: lts-21.1