Add server flag to pandoc-cli.

This allows the executable to be built without support for
"server mode."

INSTALL.md

@@ -215,8 +215,6 @@ The easiest way to build pandoc from source is to use [stack][stack]:
     `pandoc` executable into `~/.local/bin`, which you should
     add to your `PATH`.  This process will take a while, and
     will consume a considerable amount of disk space.
-    If you also want the `pandoc-server` executable, add
-    `--flag pandoc:server` to the above command.
 
 
 ### Quick cabal method
@@ -238,9 +236,6 @@ The easiest way to build pandoc from source is to use [stack][stack]:
     on linux/unix/macOS and in `%APPDATA%\cabal\bin` on Windows.
     Make sure this directory is in your path.
 
-    If you also want the `pandoc-server` executable, add
-    `-fserver` to the above command.
-
     If you want to install a modified or development version
     of pandoc instead, switch to the source directory and do
     as above, but without the 'pandoc':
@@ -292,7 +287,9 @@ You will need cabal version 2.0 or higher.
 
     - `lua53`: embed support for Lua 5.3 instead of 5.4.
 
-    - `server`:  build the `pandoc-server` executable.
+    - `server`:  compile in support for running in HTTP server
+      mode when the executable is renamed (or symlinked as)
+      `pandoc-server`.
 
 3.  Build:
 

pandoc-cli/pandoc-cli.cabal

@@ -21,6 +21,10 @@ source-repository head
   type:          git
   location:      git://github.com/jgm/pandoc.git
 
+flag server
+  Description:   Include support for running pandoc as an HTTP server.
+  Default:       True
+
 common common-options
   default-language: Haskell2010
   build-depends:    base         >= 4.12 && < 5
@@ -33,7 +37,6 @@ common common-options
                     -Wpartial-fields
                     -Wmissing-signatures
                     -fhide-source-paths
-                    -- -Wmissing-export-lists
 
   if impl(ghc >= 8.10)
     ghc-options:    -Wunused-packages
@@ -54,9 +57,11 @@ executable pandoc
   hs-source-dirs:  src
   main-is:         pandoc.hs
   buildable:       True
-  build-depends:   pandoc == 2.19.2,
-                   pandoc-server >= 0.1 && < 0.2,
-                   hslua-cli >= 1.0 && < 1.1,
-                   wai-extra >= 3.0.24,
-                   warp,
-                   safe
+  build-depends:   pandoc,
+                   hslua-cli >= 1.0 && < 1.1
+  if flag(server)
+    build-depends:   pandoc-server >= 0.1 && < 0.2,
+                     wai-extra >= 3.0.24,
+                     warp,
+                     safe
+    cpp-options:     -D_SERVER

pandoc-cli/src/pandoc.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE CPP #-}
 {- |
    Module      : Main
    Copyright   : Copyright (C) 2006-2022 John MacFarlane
@@ -19,23 +20,38 @@ import Text.Pandoc.App (convertWithOpts, defaultOpts, options, parseOptions)
 import Text.Pandoc.Class (runIOorExplode)
 import Text.Pandoc.Error (handleError)
 import Text.Pandoc.Lua (runLua)
-import Text.Pandoc.Server (ServerOpts(..), parseServerOpts, app)
 import Text.Pandoc.Shared (pandocVersion)
-import Safe (readDef)
-import System.Environment (getProgName, lookupEnv)
+import System.Environment (getProgName)
+#ifdef _SERVER
 import qualified Network.Wai.Handler.CGI as CGI
 import qualified Network.Wai.Handler.Warp as Warp
 import Network.Wai.Middleware.Timeout (timeout)
+import Text.Pandoc.Server (ServerOpts(..), parseServerOpts, app)
+import Safe (readDef)
+import System.Environment (lookupEnv)
+#else
+import System.IO (hPutStrLn, stderr)
+import System.Exit (exitWith, ExitCode(ExitFailure))
+#endif
 
 main :: IO ()
 main = E.handle (handleError . Left) $ do
   prg <- getProgName
-  cgiTimeout <- maybe 2 (readDef 2) <$> lookupEnv "PANDOC_SERVER_TIMEOUT"
   case prg of
-    "pandoc-server.cgi" -> CGI.run (timeout cgiTimeout app)
+    "pandoc-server.cgi" -> do
+#ifdef _SERVER
+      cgiTimeout <- maybe 2 (readDef 2) <$> lookupEnv "PANDOC_SERVER_TIMEOUT"
+      CGI.run (timeout cgiTimeout app)
+#else
+      serverUnsupported
+#endif
     "pandoc-server" -> do
+#ifdef _SERVER
       sopts <- parseServerOpts
       Warp.run (serverPort sopts) (timeout (serverTimeout sopts) app)
+#else
+      serverUnsupported
+#endif
     "pandoc-lua" -> do
       let settings = Settings
             { settingsVersionInfo = "\nEmbedded in pandoc " <> pandocVersion
@@ -43,3 +59,11 @@ main = E.handle (handleError . Left) $ do
             }
       runStandalone settings
     _ -> parseOptions options defaultOpts >>= convertWithOpts
+
+#ifndef _SERVER
+serverUnsupported :: IO ()
+serverUnsupported = do
+  hPutStrLn stderr $ "Server mode unsupported.\n" <>
+                     "Pandoc was not compiled with the 'server' flag."
+  exitWith $ ExitFailure 4
+#endif