Add pre and post build hooks

Run a program (named "preBuildHook") before doing a package build and
another program (named "postBuildHook") after the package is built.

These two programs simply need to be on the users $PATH variable and
are completely generic.

Co-authored: Moritz Angermann <[email protected]>

cabal-install/src/Distribution/Client/ProjectBuilding/UnpackedPackage.hs

@@ -678,7 +678,54 @@ buildAndInstallUnpackedPackage
           runConfigure
         PBBuildPhase{runBuild} -> do
           noticeProgress ProgressBuilding
-          runBuild
+          -- run preBuildHook. If it returns with 0, we assume the build was
+          -- successful. If not, run the build.
+          code <- rawSystemExitCode verbosity (Just srcdir) "preBuildHook" [
+              (unUnitId $ installedUnitId rpkg)
+            , (getSymbolicPath srcdir)
+            , (getSymbolicPath builddir)
+            ] `catchIO` (\_ -> return (ExitFailure 10))
+          when (code /= ExitSuccess) $ do
+            runBuild
+            -- not sure, if we want to care about a failed postBuildHook?
+            void $ rawSystemExitCode verbosity (Just srcdir) "postBuildHook" [
+                (unUnitId $ installedUnitId rpkg)
+              , (getSymbolicPath srcdir)
+              , (getSymbolicPath builddir)
+              ] `catchIO` (\_ -> return (ExitFailure 10))
+
+@@ -680,20 +680,29 @@
+            noticeProgress ProgressBuilding
+            -- run preBuildHook. If it returns with 0, we assume the build was
+            -- successful. If not, run the build.
+          code <-
+            rawSystemExitCode
+              verbosity
+              (Just srcdir)
+              "preBuildHook"
+              [ (unUnitId $ installedUnitId rpkg)
+              , (getSymbolicPath srcdir)
+              , (getSymbolicPath builddir)
+              ]
+              `catchIO` (\_ -> return (ExitFailure 10))
+            when (code /= ExitSuccess) $ do
+              runBuild
+              -- not sure, if we want to care about a failed postBuildHook?
+            void $
+              rawSystemExitCode
+                verbosity
+                (Just srcdir)
+                "postBuildHook"
+                [ (unUnitId $ installedUnitId rpkg)
+                , (getSymbolicPath srcdir)
+                , (getSymbolicPath builddir)
+                ]
+                `catchIO` (\_ -> return (ExitFailure 10))
+          PBHaddockPhase{runHaddock} -> do
+            noticeProgress ProgressHaddock
+            runHaddock
+
+
         PBHaddockPhase{runHaddock} -> do
           noticeProgress ProgressHaddock
           runHaddock