T.P.App: extract submodule T.P.App.FormatHeuristics

Format guessing is used for input and output options and should be
shared.

3 files changed, 96 insertions, 57 deletions

diff --git a/pandoc.cabal b/pandoc.cabal
index 7b173a88c..c34d3d461 100644
--- a/pandoc.cabal
+++ b/pandoc.cabal
@@ -522,6 +522,7 @@ library
                    Text.Pandoc.BCP47,
                    Text.Pandoc.Class
   other-modules:   Text.Pandoc.App.CommandLineOptions,
+                   Text.Pandoc.App.FormatHeuristics,
                    Text.Pandoc.App.Opt,
                    Text.Pandoc.App.OutputSettings,
                    Text.Pandoc.Filter.JSON,
diff --git a/src/Text/Pandoc/App.hs b/src/Text/Pandoc/App.hs
index 809165c2e..a14e4e017 100644
--- a/src/Text/Pandoc/App.hs
+++ b/src/Text/Pandoc/App.hs
@@ -62,6 +62,7 @@ import System.FilePath
 import System.IO (nativeNewline, stdout)
 import qualified System.IO as IO (Newline (..))
 import Text.Pandoc
+import Text.Pandoc.App.FormatHeuristics (formatFromFilePaths)
 import Text.Pandoc.App.Opt (Opt (..), LineEnding (..), defaultOpts)
 import Text.Pandoc.App.CommandLineOptions (parseOptions, options)
 import Text.Pandoc.App.OutputSettings (OutputSettings (..), optToOutputSettings)
@@ -337,63 +338,6 @@ readMetaValue s = case YAML.decodeStrict (UTF8.fromString s) of
                                              -> MetaBool b
                        _                     -> MetaString s
 
--- Determine default reader based on source file extensions.
-formatFromFilePaths :: String -> [FilePath] -> String
-formatFromFilePaths fallback [] = fallback
-formatFromFilePaths fallback (x:xs) =
-  case formatFromFilePath x of
-    Just f     -> f
-    Nothing    -> formatFromFilePaths fallback xs
-
--- Determine format based on file extension
-formatFromFilePath :: FilePath -> Maybe String
-formatFromFilePath x =
-  case takeExtension (map toLower x) of
-    ".adoc"     -> Just "asciidoc"
-    ".asciidoc" -> Just "asciidoc"
-    ".context"  -> Just "context"
-    ".ctx"      -> Just "context"
-    ".db"       -> Just "docbook"
-    ".doc"      -> Just "doc"  -- so we get an "unknown reader" error
-    ".docx"     -> Just "docx"
-    ".dokuwiki" -> Just "dokuwiki"
-    ".epub"     -> Just "epub"
-    ".fb2"      -> Just "fb2"
-    ".htm"      -> Just "html"
-    ".html"     -> Just "html"
-    ".icml"     -> Just "icml"
-    ".json"     -> Just "json"
-    ".latex"    -> Just "latex"
-    ".lhs"      -> Just "markdown+lhs"
-    ".ltx"      -> Just "latex"
-    ".markdown" -> Just "markdown"
-    ".md"       -> Just "markdown"
-    ".ms"       -> Just "ms"
-    ".muse"     -> Just "muse"
-    ".native"   -> Just "native"
-    ".odt"      -> Just "odt"
-    ".opml"     -> Just "opml"
-    ".org"      -> Just "org"
-    ".pdf"      -> Just "pdf"  -- so we get an "unknown reader" error
-    ".pptx"     -> Just "pptx"
-    ".roff"     -> Just "ms"
-    ".rst"      -> Just "rst"
-    ".rtf"      -> Just "rtf"
-    ".s5"       -> Just "s5"
-    ".t2t"      -> Just "t2t"
-    ".tei"      -> Just "tei"
-    ".tei.xml"  -> Just "tei"
-    ".tex"      -> Just "latex"
-    ".texi"     -> Just "texinfo"
-    ".texinfo"  -> Just "texinfo"
-    ".text"     -> Just "markdown"
-    ".textile"  -> Just "textile"
-    ".txt"      -> Just "markdown"
-    ".wiki"     -> Just "mediawiki"
-    ".xhtml"    -> Just "html"
-    ['.',y]     | y `elem` ['1'..'9'] -> Just "man"
-    _           -> Nothing
-
 -- Transformations of a Pandoc document post-parsing:
 
 applyTransforms :: Monad m => [Transform] -> Pandoc -> m Pandoc
diff --git a/src/Text/Pandoc/App/FormatHeuristics.hs b/src/Text/Pandoc/App/FormatHeuristics.hs
new file mode 100644
index 000000000..c8dbcd645
--- /dev/null
+++ b/src/Text/Pandoc/App/FormatHeuristics.hs
@@ -0,0 +1,94 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+{-
+Copyright (C) 2006-2018 John MacFarlane <jgm@berkeley.edu>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+-}
+
+{- |
+   Module      : Text.Pandoc.App.FormatHeuristics
+   Copyright   : Copyright (C) 2006-2018 John MacFarlane
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : John MacFarlane <jgm@berkeley@edu>
+   Stability   : alpha
+   Portability : portable
+
+Guess the format of a file from its name.
+-}
+module Text.Pandoc.App.FormatHeuristics
+  ( formatFromFilePaths
+  ) where
+
+import Prelude
+import Data.Char (toLower)
+import System.FilePath (takeExtension)
+
+-- Determine default reader based on source file extensions.
+formatFromFilePaths :: String -> [FilePath] -> String
+formatFromFilePaths fallback [] = fallback
+formatFromFilePaths fallback (x:xs) =
+  case formatFromFilePath x of
+    Just f     -> f
+    Nothing    -> formatFromFilePaths fallback xs
+
+-- Determine format based on file extension
+formatFromFilePath :: FilePath -> Maybe String
+formatFromFilePath x =
+  case takeExtension (map toLower x) of
+    ".adoc"     -> Just "asciidoc"
+    ".asciidoc" -> Just "asciidoc"
+    ".context"  -> Just "context"
+    ".ctx"      -> Just "context"
+    ".db"       -> Just "docbook"
+    ".doc"      -> Just "doc"  -- so we get an "unknown reader" error
+    ".docx"     -> Just "docx"
+    ".dokuwiki" -> Just "dokuwiki"
+    ".epub"     -> Just "epub"
+    ".fb2"      -> Just "fb2"
+    ".htm"      -> Just "html"
+    ".html"     -> Just "html"
+    ".icml"     -> Just "icml"
+    ".json"     -> Just "json"
+    ".latex"    -> Just "latex"
+    ".lhs"      -> Just "markdown+lhs"
+    ".ltx"      -> Just "latex"
+    ".markdown" -> Just "markdown"
+    ".md"       -> Just "markdown"
+    ".ms"       -> Just "ms"
+    ".muse"     -> Just "muse"
+    ".native"   -> Just "native"
+    ".odt"      -> Just "odt"
+    ".opml"     -> Just "opml"
+    ".org"      -> Just "org"
+    ".pdf"      -> Just "pdf"  -- so we get an "unknown reader" error
+    ".pptx"     -> Just "pptx"
+    ".roff"     -> Just "ms"
+    ".rst"      -> Just "rst"
+    ".rtf"      -> Just "rtf"
+    ".s5"       -> Just "s5"
+    ".t2t"      -> Just "t2t"
+    ".tei"      -> Just "tei"
+    ".tei.xml"  -> Just "tei"
+    ".tex"      -> Just "latex"
+    ".texi"     -> Just "texinfo"
+    ".texinfo"  -> Just "texinfo"
+    ".text"     -> Just "markdown"
+    ".textile"  -> Just "textile"
+    ".txt"      -> Just "markdown"
+    ".wiki"     -> Just "mediawiki"
+    ".xhtml"    -> Just "html"
+    ['.',y]     | y `elem` ['1'..'9'] -> Just "man"
+    _           -> Nothing