pandoc-cli: Allow building a binary without Lua support

Disabling the `lua` cabal flag will result in a binary without Lua.

4 files changed, 76 insertions, 24 deletions

diff --git a/pandoc-cli/lua/PandocCLI/Lua.hs b/pandoc-cli/lua/PandocCLI/Lua.hs
new file mode 100644
index 000000000..6507587c8
--- /dev/null
+++ b/pandoc-cli/lua/PandocCLI/Lua.hs
@@ -0,0 +1,35 @@
+{-# LANGUAGE OverloadedStrings #-}
+{- |
+   Module      : PandocCLI.Lua
+   Copyright   : © 2022 Albert Krewinkel
+   License     : GPL-2.0-or-later
+   Maintainer  : Albert Krewinkel <[email protected]>
+
+Functions to run the pandoc Lua scripting engine.
+-}
+module PandocCLI.Lua (runLuaInterpreter, getEngine) where
+
+import Control.Monad ((<=<))
+import HsLua.CLI (EnvBehavior (..), Settings (..), runStandalone)
+import Text.Pandoc.Class (runIOorExplode)
+import Text.Pandoc.Error (handleError)
+import Text.Pandoc.Lua (runLua, runLuaNoEnv, getEngine)
+import Text.Pandoc.Shared (pandocVersionText)
+
+-- | Runs pandoc as a Lua interpreter that is (mostly) compatible with
+-- the default @lua@ program shipping with Lua.
+runLuaInterpreter :: String    -- ^ Program name
+                  -> [String]  -- ^ Command line arguments
+                  -> IO ()
+runLuaInterpreter progName args = do
+  let settings = Settings
+        { settingsVersionInfo = "\nEmbedded in pandoc " <> pandocVersionText
+        , settingsRunner = runner
+        }
+  runStandalone settings progName args
+  where
+    runner envBehavior =
+      let runLua' = case envBehavior of
+                      IgnoreEnvVars  -> runLuaNoEnv
+                      ConsultEnvVars -> runLua
+      in handleError <=< runIOorExplode . runLua'
diff --git a/pandoc-cli/no-lua/PandocCLI/Lua.hs b/pandoc-cli/no-lua/PandocCLI/Lua.hs
new file mode 100644
index 000000000..350a4cdbc
--- /dev/null
+++ b/pandoc-cli/no-lua/PandocCLI/Lua.hs
@@ -0,0 +1,26 @@
+{-# LANGUAGE OverloadedStrings #-}
+{- |
+   Module      : PandocCLI.Lua
+   Copyright   : © 2022 Albert Krewinkel
+   License     : GPL-2.0-or-later
+   Maintainer  : Albert Krewinkel <[email protected]>
+
+Placeholder values to be used when pandoc is compiled without support
+for the Lua scripting engine.
+-}
+module PandocCLI.Lua (runLuaInterpreter, getEngine) where
+
+import Control.Monad.IO.Class (MonadIO)
+import Text.Pandoc.Error (PandocError (PandocNoScriptingEngine), handleError)
+import Text.Pandoc.Scripting (ScriptingEngine, noEngine)
+
+-- | Raises an error, reporting that the scripting engine is unavailable.
+runLuaInterpreter :: String    -- ^ Program name
+                  -> [String]  -- ^ Command line arguments
+                  -> IO ()
+runLuaInterpreter _progName _args = do
+  handleError (Left PandocNoScriptingEngine)
+
+-- | Placeholder scripting engine.
+getEngine :: MonadIO m => m ScriptingEngine
+getEngine = pure noEngine
diff --git a/pandoc-cli/pandoc-cli.cabal b/pandoc-cli/pandoc-cli.cabal
index 9a3e5ff2d..82437d441 100644
--- a/pandoc-cli/pandoc-cli.cabal
+++ b/pandoc-cli/pandoc-cli.cabal
@@ -21,6 +21,11 @@ source-repository head
   type:          git
   location:      git://github.com/jgm/pandoc.git
 
+flag lua
+  description:   Support custom modifications and conversions with the
+                 pandoc Lua scripting engine.
+  default:       True
+
 flag server
   Description:   Include support for running pandoc as an HTTP server.
   Default:       True
@@ -58,9 +63,8 @@ executable pandoc
   main-is:         pandoc.hs
   buildable:       True
   build-depends:   pandoc >= 3.0,
-                   pandoc-lua-engine >= 0.1 && < 0.2,
-                   hslua-cli >= 1.2 && < 1.3
-  other-modules:   PandocCLI.Server
+  other-modules:   PandocCLI.Lua
+                 , PandocCLI.Server
   if flag(server)
     build-depends:   pandoc-server >= 0.1 && < 0.2,
                      wai-extra >= 3.0.24,
@@ -69,3 +73,10 @@ executable pandoc
     hs-source-dirs:  server
   else
     hs-source-dirs:  no-server
+
+  if flag(lua)
+    build-depends:   hslua-cli         >= 1.2 && < 1.3,
+                     pandoc-lua-engine >= 0.1 && < 0.2
+    hs-source-dirs:  lua
+  else
+    hs-source-dirs:  no-lua
diff --git a/pandoc-cli/src/pandoc.hs b/pandoc-cli/src/pandoc.hs
index 306b2dc8a..1b95d898e 100644
--- a/pandoc-cli/src/pandoc.hs
+++ b/pandoc-cli/src/pandoc.hs
@@ -12,17 +12,13 @@ Parses command-line options and calls the appropriate readers and
 writers.
 -}
 module Main where
-import Control.Monad ((<=<))
 import qualified Control.Exception as E
-import HsLua.CLI (EnvBehavior (..), Settings (..), runStandalone)
 import System.Environment (getArgs, getProgName)
 import Text.Pandoc.App ( convertWithOpts, defaultOpts, options
                        , parseOptionsFromArgs)
-import Text.Pandoc.Class (runIOorExplode)
 import Text.Pandoc.Error (handleError)
-import Text.Pandoc.Lua (getEngine, runLua, runLuaNoEnv)
-import Text.Pandoc.Shared (pandocVersionText)
 import qualified Text.Pandoc.UTF8 as UTF8
+import PandocCLI.Lua
 import PandocCLI.Server
 
 main :: IO ()
@@ -42,19 +38,3 @@ main = E.handle (handleError . Left) $ do
           let cliOpts = options engine
           opts <- parseOptionsFromArgs cliOpts defaultOpts prg rawArgs
           convertWithOpts engine opts
-
--- | Runs pandoc as a Lua interpreter that is (mostly) compatible with
--- the default @lua@ program shipping with Lua.
-runLuaInterpreter :: String -> [String] -> IO ()
-runLuaInterpreter progName args = do
-  let settings = Settings
-        { settingsVersionInfo = "\nEmbedded in pandoc " <> pandocVersionText
-        , settingsRunner = runner
-        }
-  runStandalone settings progName args
-  where
-    runner envBehavior =
-      let runLua' = case envBehavior of
-                      IgnoreEnvVars  -> runLuaNoEnv
-                      ConsultEnvVars -> runLua
-      in handleError <=< runIOorExplode . runLua'