Remove initial check for pdf creating program.

Instead, just try running it and raise the exception if it
isn't found at that point.

This improves things for users of Cygwin on Windows, where
the executable won't be found by `findExecutable` unless
`.exe` is added.

The same exception is raised as before, but at a later
point.

Closes #3819.

src/Text/Pandoc/App.hs

@@ -485,10 +485,6 @@ convertWithOpts opts = do
                                   | html5Output   -> "wkhtmltopdf"
                                   | msOutput      -> "pdfroff"
                                   | otherwise     -> optLaTeXEngine opts
-                -- check for pdf creating program
-                mbPdfProg <- liftIO $ findExecutable pdfprog
-                when (isNothing mbPdfProg) $ liftIO $ E.throwIO $
-                       PandocPDFProgramNotFoundError pdfprog
 
                 res <- makePDF pdfprog f writerOptions verbosity media doc
                 case res of

src/Text/Pandoc/PDF.hs

@@ -50,7 +50,9 @@ import System.Exit (ExitCode (..))
 import System.FilePath
 import System.IO (stdout)
 import System.IO.Temp (withTempDirectory, withTempFile)
+import System.IO.Error (IOError, isDoesNotExistError)
 import Text.Pandoc.Definition
+import Text.Pandoc.Error (PandocError(PandocPDFProgramNotFoundError))
 import Text.Pandoc.MediaBag
 import Text.Pandoc.MIME (getMimeType)
 import Text.Pandoc.Options (HTMLMathMethod (..), WriterOptions (..))
@@ -193,7 +195,12 @@ tex2pdf' verbosity args tmpDir program source = do
   let numruns = if "\\tableofcontents" `T.isInfixOf` source
                    then 3  -- to get page numbers
                    else 2  -- 1 run won't give you PDF bookmarks
-  (exit, log', mbPdf) <- runTeXProgram verbosity program args 1 numruns tmpDir source
+  (exit, log', mbPdf) <- E.catch
+    (runTeXProgram verbosity program args 1 numruns tmpDir source)
+    (\(e :: IOError) -> if isDoesNotExistError e
+                           then E.throwIO $
+                                 PandocPDFProgramNotFoundError program
+                           else E.throwIO e)
   case (exit, mbPdf) of
        (ExitFailure _, _)      -> do
           let logmsg = extractMsg log'
@@ -321,8 +328,13 @@ ms2pdf verbosity args source = do
     putStrLn $ "[makePDF] Contents:\n"
     putStr $ T.unpack source
     putStr "\n"
-  (exit, out) <- pipeProcess (Just env') "pdfroff" args
-                     (BL.fromStrict $ UTF8.fromText source)
+  (exit, out) <- E.catch
+    (pipeProcess (Just env') "pdfroff" args
+                     (BL.fromStrict $ UTF8.fromText source))
+    (\(e :: IOError) -> if isDoesNotExistError e
+                           then E.throwIO $
+                                  PandocPDFProgramNotFoundError "pdfroff"
+                           else E.throwIO e)
   when (verbosity >= INFO) $ do
     BL.hPutStr stdout out
     putStr "\n"
@@ -350,7 +362,12 @@ html2pdf verbosity args source = do
     putStrLn $ "[makePDF] Contents of " ++ file ++ ":"
     BL.readFile file >>= BL.putStr
     putStr "\n"
-  (exit, out) <- pipeProcess (Just env') "wkhtmltopdf" programArgs BL.empty
+  (exit, out) <- E.catch
+    (pipeProcess (Just env') "wkhtmltopdf" programArgs BL.empty)
+    (\(e :: IOError) -> if isDoesNotExistError e
+                           then E.throwIO $
+                                  PandocPDFProgramNotFoundError "wkhtml2pdf"
+                           else E.throwIO e)
   removeFile file
   when (verbosity >= INFO) $ do
     BL.hPutStr stdout out
@@ -397,7 +414,12 @@ context2pdf verbosity tmpDir source = inDirectory tmpDir $ do
     putStrLn $ "[makePDF] Contents of " ++ file ++ ":"
     BL.readFile file >>= BL.putStr
     putStr "\n"
-  (exit, out) <- pipeProcess (Just env') "context" programArgs BL.empty
+  (exit, out) <- E.catch
+    (pipeProcess (Just env') "context" programArgs BL.empty)
+    (\(e :: IOError) -> if isDoesNotExistError e
+                           then E.throwIO $
+                                  PandocPDFProgramNotFoundError "context"
+                           else E.throwIO e)
   when (verbosity >= INFO) $ do
     BL.hPutStr stdout out
     putStr "\n"