Add a flag to disable the preview server

.ghci

@@ -1 +1 @@
-:set -isrc -isrc-interval -itests -idist/build/autogen
+:set -isrc -isrc-interval -itests -idist/build/autogen -DPREVIEW_SERVER

hakyll.cabal

@@ -50,6 +50,10 @@ Source-Repository head
   Type:     git
   Location: git://github.com/jaspervdj/hakyll.git
 
+Flag previewServer
+  Description: Include the preview server
+  default:     True
+
 Library
   Ghc-Options:    -Wall
   Hs-Source-Dirs: src
@@ -72,8 +76,6 @@ Library
     process     >= 1.0   && < 1.4,
     regex-base  >= 0.93  && < 1.0,
     regex-pcre  >= 0.93  && < 1.0,
-    snap-core   >= 0.5.1 && < 0.6,
-    snap-server >= 0.5.1 && < 0.6,
     tagsoup     >= 0.12  && < 0.13,
     time        >= 1.1   && < 1.3,
     unix        >= 2.4   && < 2.6
@@ -113,8 +115,6 @@ Library
     Hakyll.Web.Page.Read
     Hakyll.Web.Pandoc
     Hakyll.Web.Pandoc.FileType
-    Hakyll.Web.Preview.Poll
-    Hakyll.Web.Preview.Server
     Hakyll.Web.RelativizeUrls
     Hakyll.Web.Tags
     Hakyll.Web.Template
@@ -131,3 +131,13 @@ Library
     Hakyll.Web.Template.Read.Hakyll
     Hakyll.Web.Template.Read.Hamlet
     Paths_hakyll
+
+  If flag(previewServer)
+    Build-depends:
+      snap-core   >= 0.5.1 && < 0.6,
+      snap-server >= 0.5.1 && < 0.6
+    Cpp-Options:
+      -DPREVIEW_SERVER
+    Other-Modules:
+      Hakyll.Web.Preview.Poll
+      Hakyll.Web.Preview.Server

src/Hakyll/Main.hs

@@ -1,25 +1,30 @@
 -- | Module providing the main hakyll function and command-line argument parsing
 --
+{-# LANGUAGE CPP #-}
 module Hakyll.Main
     ( hakyll
     , hakyllWith
     ) where
 
-import Control.Applicative ((<$>))
-import Control.Concurrent (forkIO)
 import Control.Monad (when)
 import System.Directory (doesDirectoryExist, removeDirectoryRecursive)
 import System.Environment (getProgName, getArgs)
 import System.Process (system)
-import qualified Data.Set as S
 
 import Hakyll.Core.Configuration
-import Hakyll.Core.Resource
 import Hakyll.Core.Run
 import Hakyll.Core.Rules
+
+#ifdef PREVIEW_SERVER
+import Control.Applicative ((<$>))
+import Control.Concurrent (forkIO)
+import qualified Data.Set as S
+
+import Hakyll.Core.Resource
 import Hakyll.Core.Rules.Internal
 import Hakyll.Web.Preview.Poll
 import Hakyll.Web.Preview.Server
+#endif
 
 -- | This usualy is the function with which the user runs the hakyll compiler
 --
@@ -83,11 +88,17 @@ help = do
         , name ++ " rebuild         Clean up and build again"
         , name ++ " server [port]   Run a local test server"
         , name ++ " deploy          Upload/deploy your site"
+        , ""
         ]
 
+#ifndef PREVIEW_SERVER
+    previewServerDisabled
+#endif
+
 -- | Preview the site
 --
 preview :: HakyllConfiguration -> RulesM a -> Int -> IO ()
+#ifdef PREVIEW_SERVER
 preview conf rules port = do
     -- Fork a thread polling for changes
     _ <- forkIO $ previewPoll conf update
@@ -96,6 +107,9 @@ preview conf rules port = do
     server conf port
   where
     update = map unResource . S.toList . rulesResources <$> run conf rules
+#else
+preview _ _ _ = previewServerDisabled
+#endif
 
 -- | Rebuild the site
 --
@@ -107,15 +121,33 @@ rebuild conf rules = do
 -- | Start a server
 --
 server :: HakyllConfiguration -> Int -> IO ()
+#ifdef PREVIEW_SERVER
 server conf port = do
     let destination = destinationDirectory conf
     staticServer destination preServeHook port
   where
     preServeHook _ = return ()
+#else
+server _ _ = previewServerDisabled
+#endif
 
--- Upload the site
+-- | Upload the site
 --
 deploy :: HakyllConfiguration -> IO ()
 deploy conf = do
     _ <- system $ deployCommand conf
     return ()
+
+-- | Print a warning message about the preview serving not being enabled
+--
+#ifndef PREVIEW_SERVER
+previewServerDisabled :: IO ()
+previewServerDisabled =
+    mapM_ putStrLn
+        [ "PREVIEW SERVER"
+        , ""
+        , "The preview server is not enabled in the version of Hakyll. To"
+        , "enable it, set the flag to True and recompile Hakyll."
+        , "Alternatively, use an external tool to serve your site directory."
+        ]
+#endif