allow picking patches from files

Main.hs

@@ -344,7 +344,10 @@ runCmd CmdPatch {..} cfg = do
   withSystemTempDirectory "werge-patch" $ \workdir -> do
     let f = workdir </> "file"
     bracketFile patchMy ReadMode $ \h -> hSplitToFile cfg h f
-    _ <- runPatch f stdin
+    _ <-
+      case patchInput of
+        Nothing -> runPatch f stdin
+        Just path -> bracketFile path ReadMode $ runPatch f
     conflicted <- pmerge f >>= format cfg stdout -- TODO try to resolve more?
     if conflicted
       then exitWith (ExitFailure 1)

Opts.hs

@@ -230,6 +230,7 @@ data Command
       }
   | CmdPatch
       { patchMy :: FilePath
+      , patchInput :: Maybe FilePath
       }
   | CmdBreak
   | CmdGlue
@@ -295,6 +296,12 @@ cmdDiff = do
 cmdPatch :: Parser Command
 cmdPatch = do
   patchMy <- strArgument $ metavar "MYFILE" <> help "File to be modified"
+  patchInput <-
+    optional . strOption
+      $ long "patch"
+          <> short 'p'
+          <> metavar "PATCH"
+          <> help "File with the patch (default: stdin)"
   pure CmdPatch {..}
 
 -- TODO have some option to output the (partially merged) my/old/your files so
@@ -314,7 +321,7 @@ cmd =
             $ progDesc "Find differences between two files"
         , command "patch"
             $ info cmdPatch
-            $ progDesc "Apply a patch from `diff' to file"
+            $ progDesc "Modify a file using a patch from `diff'"
         , command "break"
             $ info (pure CmdBreak)
             $ progDesc "Break text to tokens"