Hadrian: fix dyn_o/dyn_hi rule (#17534)

1 files changed, 16 insertions, 1 deletions

diff --git a/hadrian/src/Rules/Compile.hs b/hadrian/src/Rules/Compile.hs
index ee395d4d75..12a8707f31 100644
--- a/hadrian/src/Rules/Compile.hs
+++ b/hadrian/src/Rules/Compile.hs
@@ -55,7 +55,22 @@ compilePackage rs = do
         &%> \ [dyn_o, _dyn_hi] -> do
           p <- platformSupportsSharedLibs
           if p
-            then need [dyn_o -<.> "o", dyn_o -<.> "hi"]
+            then do
+               -- We `need` ".o/.hi" because GHC is called with `-dynamic-too`
+               -- and builds ".dyn_o/.dyn_hi" too.
+               changed <- needHasChanged [dyn_o -<.> "o", dyn_o -<.> "hi"]
+
+               -- If for some reason a previous Hadrian execution has been
+               -- interrupted after the rule for .o/.hi generation has completed
+               -- but before the current rule for .dyn_o/.dyn_hi has completed,
+               -- or if some of the dynamic artifacts have been removed by the
+               -- user, "needing" the non dynamic artifacts is not enough as
+               -- Shake won't execute the associated action. Hence we detect
+               -- this case and we explictly build the dynamic artifacts here:
+               case changed of
+                  [] -> compileHsObjectAndHi rs dyn_o
+                  _  -> pure ()
+
             else compileHsObjectAndHi rs dyn_o
 
       forM_ ((,) <$> hsExts <*> wayPats) $ \ ((oExt, hiExt), wayPat) ->