From 752a2b80a670ded37027e97c0a1070c2ffa089ee Mon Sep 17 00:00:00 2001
From: Charles Durham <cpdurham@protonmail.com>
Date: Mon, 10 May 2021 10:06:01 -0400
Subject: [PATCH] added 'qAddDependentFile' to 'embedFileIfExists' and some
 tests

---
 Data/FileEmbed.hs | 17 +++++++++++------
 file-embed.cabal  |  1 +
 test/main.hs      |  7 +++++++
 3 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/Data/FileEmbed.hs b/Data/FileEmbed.hs
index a9edb92..5846e70 100644
--- a/Data/FileEmbed.hs
+++ b/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.
 --
diff --git a/file-embed.cabal b/file-embed.cabal
index 5ba1889..894a586 100644
--- a/file-embed.cabal
+++ b/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
 
diff --git a/test/main.hs b/test/main.hs
index 31c4067..4b665c8 100644
--- a/test/main.hs
+++ b/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