Merge pull request #167 from mgsloan/log-recompilation-info

Log information about xmonad compile + avoid unnecessary recompile

CHANGES.md

@@ -43,6 +43,18 @@
   * Restored compatability with GHC version prior to 8.0.1 by removing the
     dependency on directory version 1.2.3.
 
+  * xmonad no longer always recompile on startup. Now it only does so if the
+    executable does not have the name that would be used for the compilation
+    output. The purpose of recompiling and executing the results in this case is
+    so that the `xmonad` executable in the package can be used with custom
+    configurations.
+
+### Enhancements
+
+  * Whenever xmonad recompiles, it now explains how it is attempting to
+    recompile, by outputting logs to stderr. If you are using xmonad as a custom
+    X session, then this will end up in a `.xsession-errors` file.
+
 ## 0.13 (February 10, 2017)
 
 ### Breaking Changes

src/XMonad/Core.hs

@@ -607,9 +607,36 @@ recompile force = io $ do
 
     useBuildscript <- do
       exists <- doesFileExist buildscript
-      if exists then isExecutable buildscript else return False
+      if exists
+        then do
+          isExe <- isExecutable buildscript
+          if isExe
+            then do
+              trace $ "XMonad will use build script at " ++ show buildscript ++ " to recompile."
+              return True
+            else do
+              trace $ unlines
+                [ "XMonad will not use build script, because " ++ show buildscript ++ " is not executable."
+                , "Suggested resolution to use it: chmod u+x " ++ show buildscript
+                ]
+              return False
+        else do
+          trace $
+            "XMonad will use ghc to recompile, because " ++ show buildscript ++ " does not exist."
+          return False
 
-    if force || useBuildscript || any (binT <) (srcT : libTs)
+    shouldRecompile <-
+      if useBuildscript || force
+        then return True
+        else if any (binT <) (srcT : libTs)
+          then do
+            trace "XMonad doing recompile because some files have changed."
+            return True
+          else do
+            trace "XMonad skipping recompile because it is not forced (e.g. via --recompile), and neither xmonad.hs nor any *.hs / *.lhs / *.hsc files in lib/ have been changed."
+            return False
+
+    if shouldRecompile
       then do
         -- temporarily disable SIGCHLD ignoring:
         uninstallSignalHandlers
@@ -622,17 +649,19 @@ recompile force = io $ do
         installSignalHandlers
 
         -- now, if it fails, run xmessage to let the user know:
-        when (status /= ExitSuccess) $ do
+        if status == ExitSuccess
-            ghcErr <- readFile err
+            then trace "XMonad recompilation process exited with success!"
-            let msg = unlines $
+            else do
-                    ["Error detected while loading xmonad configuration file: " ++ src]
+                ghcErr <- readFile err
-                    ++ lines (if null ghcErr then show status else ghcErr)
+                let msg = unlines $
-                    ++ ["","Please check the file for errors."]
+                        ["Error detected while loading xmonad configuration file: " ++ src]
-            -- nb, the ordering of printing, then forking, is crucial due to
+                        ++ lines (if null ghcErr then show status else ghcErr)
-            -- lazy evaluation
+                        ++ ["","Please check the file for errors."]
-            hPutStrLn stderr msg
+                -- nb, the ordering of printing, then forking, is crucial due to
-            forkProcess $ executeFile "xmessage" True ["-default", "okay", replaceUnicode msg] Nothing
+                -- lazy evaluation
-            return ()
+                hPutStrLn stderr msg
+                forkProcess $ executeFile "xmessage" True ["-default", "okay", replaceUnicode msg] Nothing
+                return ()
         return (status == ExitSuccess)
       else return True
  where getModTime f = E.catch (Just <$> getModificationTime f) (\(SomeException _) -> return Nothing)

src/XMonad/Main.hs

@@ -113,12 +113,18 @@ usage = do
 --
 buildLaunch ::  IO ()
 buildLaunch = do
-    recompile False
-    dir  <- getXMonadDataDir
-    args <- getArgs
     whoami <- getProgName
     let compiledConfig = "xmonad-"++arch++"-"++os
-    unless (whoami == compiledConfig) $
+    unless (whoami == compiledConfig) $ do
+      trace $ concat
+        [ "XMonad is recompiling and replacing itself another XMonad process because the current process is called "
+        , show whoami
+        , " but the compiled configuration should be called "
+        , show compiledConfig
+        ]
+      recompile False
+      dir  <- getXMonadDataDir
+      args <- getArgs
       executeFile (dir </> compiledConfig) False args Nothing
 
 sendRestart :: IO ()