hadrian: Only copy and install libffi headers when using in-tree libffi

When passed `--use-system-libffi` then we shouldn't copy and install the
headers from the system package. Instead the headers are expected to be
available as a runtime dependency on the users system.

Fixes #21485 #21487

2 files changed, 4 insertions, 2 deletions

diff --git a/hadrian/src/Rules/Generate.hs b/hadrian/src/Rules/Generate.hs
index aaa83e0060..5653bd1d25 100644
--- a/hadrian/src/Rules/Generate.hs
+++ b/hadrian/src/Rules/Generate.hs
@@ -41,13 +41,15 @@ rtsDependencies :: Expr [FilePath]
 rtsDependencies = do
     stage   <- getStage
     rtsPath <- expr (rtsBuildPath stage)
+    useSystemFfi <- expr (flag UseSystemFfi)
+
     let headers =
             [ "ghcautoconf.h", "ghcplatform.h"
             , "DerivedConstants.h"
             , "rts" -/- "EventTypes.h"
             , "rts" -/- "EventLogConstants.h"
             ]
-            ++ libffiHeaderFiles
+            ++ (if useSystemFfi then [] else libffiHeaderFiles)
     pure $ ((rtsPath -/- "include") -/-) <$> headers
 
 genapplyDependencies :: Expr [FilePath]
diff --git a/hadrian/src/Rules/Rts.hs b/hadrian/src/Rules/Rts.hs
index 59a337801f..9a18a41c46 100644
--- a/hadrian/src/Rules/Rts.hs
+++ b/hadrian/src/Rules/Rts.hs
@@ -126,7 +126,7 @@ needRtsLibffiTargets stage = do
     let headers = fmap ((rtsPath -/- "include") -/-) libffiHeaderFiles
 
     if useSystemFfi
-    then return headers
+    then return []
     else do
         -- Need Libffi
         -- This returns the dynamic library files (in the Libffi build dir).