build: Don't forget to nub extra sources

In the refactor in the previous commits we stopped nubbing the extra
build sources, resulting in accidentally passing the same object file
more than once in some invocations.

This patch resolves this by joining the extra build sources as nublists
again.

Cabal/src/Distribution/Simple/GHC/Build.hs

@@ -17,6 +17,7 @@ import Distribution.Simple.Program
 import Distribution.Simple.Utils
 import Distribution.Types.ComponentLocalBuildInfo (componentIsIndefinite)
 import Distribution.Types.ParStrat
+import Distribution.Utils.NubList (fromNubListR)
 import System.Directory hiding (exeExtension)
 import System.FilePath
 
@@ -136,4 +137,4 @@ build numJobs pkg_descr pbci = do
   -- generated from compiling Haskell modules (#842, #3294).
   buildOpts <- buildHaskellModules numJobs ghcProg pkg_descr buildTargetDir_absolute wantedWays pbci
   extraSources <- buildAllExtraSources ghcProg buildTargetDir pbci
-  linkOrLoadComponent ghcProg pkg_descr extraSources (buildTargetDir, targetDir_absolute) (wantedWays, buildOpts) pbci
+  linkOrLoadComponent ghcProg pkg_descr (fromNubListR extraSources) (buildTargetDir, targetDir_absolute) (wantedWays, buildOpts) pbci

Cabal/src/Distribution/Simple/GHC/Build/ExtraSources.hs

@@ -10,6 +10,7 @@ import Distribution.Simple.Flag
 import qualified Distribution.Simple.GHC.Internal as Internal
 import Distribution.Simple.Program.GHC
 import Distribution.Simple.Utils
+import Distribution.Utils.NubList
 
 import Distribution.Types.BuildInfo
 import Distribution.Types.Component
@@ -34,15 +35,16 @@ buildAllExtraSources
   -- ^ The build directory for this target
   -> PreBuildComponentInputs
   -- ^ The context and component being built in it.
-  -> IO [FilePath]
-  -- ^ Returns the list of extra sources that were built
-buildAllExtraSources = mconcat
-  [ buildCSources
-  , buildCxxSources
-  , buildJsSources
-  , buildAsmSources
-  , buildCmmSources
-  ]
+  -> IO (NubListR FilePath)
+  -- ^ Returns the (nubbed) list of extra sources that were built
+buildAllExtraSources =
+  mconcat
+    [ buildCSources
+    , buildCxxSources
+    , buildJsSources
+    , buildAsmSources
+    , buildCmmSources
+    ]
 
 buildCSources
   , buildCxxSources
@@ -55,7 +57,7 @@ buildCSources
     -- ^ The build directory for this target
     -> PreBuildComponentInputs
     -- ^ The context and component being built in it.
-    -> IO [FilePath]
+    -> IO (NubListR FilePath)
     -- ^ Returns the list of extra sources that were built
 buildCSources =
   buildExtraSources
@@ -137,7 +139,7 @@ buildExtraSources
   -- ^ The build directory for this target
   -> PreBuildComponentInputs
   -- ^ The context and component being built in it.
-  -> IO [FilePath]
+  -> IO (NubListR FilePath)
   -- ^ Returns the list of extra sources that were built
 buildExtraSources description componentSourceGhcOptions wantDyn viewSources ghcProg buildTargetDir =
   \PreBuildComponentInputs{buildingWhat, localBuildInfo = lbi, targetInfo} ->
@@ -233,8 +235,8 @@ buildExtraSources description componentSourceGhcOptions wantDyn viewSources ghcP
      in
       -- build any sources
       if (null sources || componentIsIndefinite clbi)
-        then return []
+        then return mempty
         else do
           info verbosity ("Building " ++ description ++ "...")
           traverse_ buildAction sources
-          return sources
+          return (toNubListR sources)

Cabal/src/Distribution/Simple/GHC/Build/Link.hs

@@ -182,7 +182,7 @@ linkLibrary
   :: FilePath
   -- ^ The library target build directory
   -> [FilePath]
-  -- ^ The list of extra lib dirs that exist (aka cleaned)
+  -- ^ The list of extra lib dirs that exist (aka "cleaned")
   -> PackageDescription
   -- ^ The package description containing this library
   -> Verbosity