servers: fix stale git commit in version

src/Simplex/Messaging/Server/Main/GitCommit.hs

@@ -6,14 +6,25 @@ module Simplex.Messaging.Server.Main.GitCommit
   ) where
 
 import Language.Haskell.TH
+import Language.Haskell.TH.Syntax (addDependentFile)
 import System.Process
 import Control.Exception
+import Control.Monad (filterM)
+import System.Directory (doesFileExist)
 import System.Exit
+import System.FilePath ((</>))
 
 gitCommit :: Q Exp
-gitCommit = stringE . commit =<< runIO (try $ readProcessWithExitCode "git" ["rev-parse", "HEAD"] "")
+gitCommit =
+  runIO gitHead >>= \case
+    Right (ExitSuccess, out, _)
+      | [commit, gitDir] <- lines out -> do
+          -- without these dependencies GHC recompilation check would not know that the commit changed.
+          -- HEAD reflog is updated on any HEAD change and, unlike branch ref files, git gc cannot remove it
+          -- mid-build; it is absent when reflogs are disabled, and addDependentFile fails on a missing file
+          mapM_ addDependentFile =<< runIO (filterM doesFileExist [gitDir </> "HEAD", gitDir </> "logs" </> "HEAD"])
+          stringE commit
+    _ -> stringE ""
   where
-    commit :: Either SomeException (ExitCode, String, String) -> String
-    commit = \case
-      Right (ExitSuccess, out, _) -> take 40 out
-      _ -> ""
+    gitHead :: IO (Either SomeException (ExitCode, String, String))
+    gitHead = try $ readProcessWithExitCode "git" ["rev-parse", "HEAD", "--git-dir"] ""