Expand and unify --keep-temp-files

Currently, `cabal repl` has a `--keep-temp-files` option, and
`cabal.project` has a `keep-temp-files` option but it only effects
Haddock builds.

This patch adds `--keep-temp-files` to `CommonSetupFlags`, making it
available to all commands. The expanded `--keep-temp-files` flag is used
for the `cabal repl` command and Haddock builds (retaining compatibility
with the previous behavior) but is also used to determine when to keep
response files.

Cabal/src/Distribution/Simple/Haddock.hs

@@ -67,12 +67,9 @@ import Distribution.Simple.Program.GHC
 import qualified Distribution.Simple.Program.HcPkg as HcPkg
 import Distribution.Simple.Program.ResponseFile
 import Distribution.Simple.Register
-import Distribution.Simple.Setup.Common
-import Distribution.Simple.Setup.Haddock
-import Distribution.Simple.Setup.Hscolour
+import Distribution.Simple.Setup
 import Distribution.Simple.SetupHooks.Internal
   ( BuildHooks (..)
-  , BuildingWhat (..)
   , noBuildHooks
   )
 import qualified Distribution.Simple.SetupHooks.Internal as SetupHooks
@@ -265,6 +262,7 @@ haddock_setupHooks
         mbWorkDir = flagToMaybe $ haddockWorkingDir flags
         comp = compiler lbi
         platform = hostPlatform lbi
+        config = configFlags lbi
 
         quickJmpFlag = haddockQuickJump flags'
         flags = case haddockTarget of
@@ -282,9 +280,7 @@ haddock_setupHooks
         flag f = fromFlag $ f flags
 
         tmpFileOpts =
-          defaultTempFileOptions
-            { optKeepTempFiles = flag haddockKeepTempFiles
-            }
+          commonSetupTempFileOptions $ configCommonFlags config
         htmlTemplate =
           fmap toPathTemplate . flagToMaybe . haddockHtmlLocation $
             flags

Cabal/src/Distribution/Simple/Setup.hs

@@ -41,6 +41,7 @@ module Distribution.Simple.Setup
   , globalCommand
   , CommonSetupFlags (..)
   , defaultCommonSetupFlags
+  , commonSetupTempFileOptions
   , ConfigFlags (..)
   , emptyConfigFlags
   , defaultConfigFlags

Cabal/src/Distribution/Simple/Setup/Common.hs

@@ -23,6 +23,7 @@ module Distribution.Simple.Setup.Common
   ( CommonSetupFlags (..)
   , defaultCommonSetupFlags
   , withCommonSetupOptions
+  , commonSetupTempFileOptions
   , CopyDest (..)
   , configureCCompiler
   , configureLinker
@@ -85,6 +86,13 @@ data CommonSetupFlags = CommonSetupFlags
   --
   -- TODO: this one should not be here, it's just that the silly
   -- UserHooks stop us from passing extra info in other ways
+  , setupKeepTempFiles :: Flag Bool
+  -- ^ When this flag is set, temporary files will be kept after building.
+  --
+  -- Note: Keeping temporary files is important functionality for HLS, which
+  -- runs @cabal repl@ with a fake GHC to get CLI arguments. It will need the
+  -- temporary files (including multi unit repl response files) to stay, even
+  -- after the @cabal repl@ command exits.
   }
   deriving (Eq, Show, Read, Generic)
 
@@ -106,6 +114,15 @@ defaultCommonSetupFlags =
     , setupDistPref = NoFlag
     , setupCabalFilePath = NoFlag
     , setupTargets = []
+    , setupKeepTempFiles = NoFlag
+    }
+
+-- | Get `TempFileOptions` that respect the `setupKeepTempFiles` flag.
+commonSetupTempFileOptions :: CommonSetupFlags -> TempFileOptions
+commonSetupTempFileOptions options =
+  TempFileOptions
+    { optKeepTempFiles =
+        fromFlagOrDefault False (setupKeepTempFiles options)
     }
 
 commonSetupOptions :: ShowOrParseArgs -> [OptionField CommonSetupFlags]
@@ -124,6 +141,14 @@ commonSetupOptions showOrParseArgs =
       setupCabalFilePath
       (\v flags -> flags{setupCabalFilePath = v})
       (reqSymbolicPathArgFlag "PATH")
+  , option
+      ""
+      ["keep-temp-files"]
+      ( "Keep temporary files."
+      )
+      setupKeepTempFiles
+      (\keepTempFiles flags -> flags{setupKeepTempFiles = keepTempFiles})
+      trueArg
       -- NB: no --working-dir flag, as that value is populated using the
       -- global flag (see Distribution.Simple.Setup.Global.globalCommand).
   ]