added 'qAddDependentFile' to 'embedFileIfExists' and some tests

Data/FileEmbed.hs

@@ -91,24 +91,29 @@ embedFile fp =
 
 -- | Maybe embed a single file in your source code depending on whether or not file exists.
 --
--- Warning: Does not use `qAddDependentFile` to force a recompile depending on changes to or appearance of the file.
+-- Warning: When a build is compiled with the file missing, a recompile when the file exists might not trigger an embed of the file.
+-- You might try to fix this by doing a clean build.
 --
 -- > import qualified Data.ByteString
 -- >
 -- > maybeMyFile :: Maybe Data.ByteString.ByteString
 -- > maybeMyFile = $(embedFileIfExists "dirName/fileName")
 embedFileIfExists :: FilePath -> Q Exp
-embedFileIfExists fp = runIO maybeFile >>= maybeBsToExp
+embedFileIfExists fp = do
+  mbs <- runIO maybeFile
+  case mbs of
+    Nothing -> [| Nothing |]
+    Just bs -> do
+#if MIN_VERSION_template_haskell(2,7,0)
+      qAddDependentFile fp
+#endif
+      [| Just $(bsToExp bs) |]
   where
     maybeFile :: IO (Maybe B.ByteString)
     maybeFile = 
       either (const Nothing) Just <$> 
       tryJust (guard . isDoesNotExistError) (B.readFile fp)
 
-    maybeBsToExp :: Maybe B.ByteString -> Q Exp
-    maybeBsToExp Nothing = [| Nothing |]
-    maybeBsToExp (Just bs) = [| Just $(bsToExp bs) |]
-
 -- | Embed a single existing file in your source code
 -- out of list a list of paths supplied.
 --

file-embed.cabal

@@ -33,6 +33,7 @@ test-suite test
     main-is: main.hs
     hs-source-dirs: test
     build-depends: base
+                 , bytestring
                  , file-embed
                  , filepath
 

test/main.hs

@@ -2,6 +2,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 
 import Control.Monad (unless)
+import qualified Data.ByteString as B (ByteString)
 import Data.FileEmbed
 import System.FilePath ((</>))
 
@@ -19,3 +20,9 @@ main = do
         ]
     let str = $(embedStringFile "test/sample/foo") :: String
     filter (/= '\r') str @?= "foo\n"
+
+    let mbs = $(embedFileIfExists "test/sample/foo")
+    mbs @?= Just "foo\r\n"
+
+    let mbs2 = $(embedFileIfExists "test/sample/foo2") :: Maybe B.ByteString
+    mbs2 @?= Nothing