From b7810b9e5375ba6ffd0bf5370cac8717cc171739 Mon Sep 17 00:00:00 2001
From: Erik de Castro Lopo <erikd@mega-nerd.com>
Date: Wed, 15 Nov 2023 12:43:17 +1100
Subject: [PATCH] Use linker capability detection to improve linker use

The function `comperSupportsGhciLibs` has been renamed to
`linkerSupportsGhciLibs` because its about the linker not the compiler.

The function `comperSupportsGhciLibs` was using the compiler version
as a proxy for whether the linker supports relocatable objects. Now
support for relocatable objects is detected by running the linker.
---
 Cabal/src/Distribution/Simple/Configure.hs  | 32 +++++++++------------
 Cabal/src/Distribution/Simple/Program/Db.hs |  7 ++++-
 changelog.d/pr-9443                         | 12 ++++++++
 3 files changed, 31 insertions(+), 20 deletions(-)
 create mode 100644 changelog.d/pr-9443

diff --git a/Cabal/src/Distribution/Simple/Configure.hs b/Cabal/src/Distribution/Simple/Configure.hs
index 1c9188a2a6b..2311c1b6e0f 100644
--- a/Cabal/src/Distribution/Simple/Configure.hs
+++ b/Cabal/src/Distribution/Simple/Configure.hs
@@ -82,6 +82,7 @@ import Distribution.Simple.PackageIndex (InstalledPackageIndex)
 import qualified Distribution.Simple.PackageIndex as PackageIndex
 import Distribution.Simple.PreProcess
 import Distribution.Simple.Program
+import Distribution.Simple.Program.Db (lookupProgramByName)
 import Distribution.Simple.Setup.Common as Setup
 import Distribution.Simple.Setup.Config as Setup
 import Distribution.Simple.Utils
@@ -767,22 +768,15 @@ configure (pkg_descr0, pbi) cfg = do
             )
           return False
 
-  let compilerSupportsGhciLibs :: Bool
-      compilerSupportsGhciLibs =
-        case compilerId comp of
-          CompilerId GHC version
-            | version > mkVersion [9, 3] && windows ->
-                False
-          CompilerId GHC _ ->
-            True
-          CompilerId GHCJS _ ->
-            True
-          _ -> False
-        where
-          windows = case compPlatform of
-            Platform _ Windows -> True
-            Platform _ _ -> False
-
+  let linkerSupportsGhciLibs :: Bool
+      linkerSupportsGhciLibs =
+        case lookupProgramByName "ld" programDb'' of
+          Nothing -> True -- NOTE: This may still fail if the linker does not support -r.
+          Just ld ->
+            case Map.lookup "Supports relocatable output" $ programProperties ld of
+              Just "YES" -> True
+              Just "NO" -> False
+              _other -> True -- NOTE: This may still fail if the linker does not support -r.
   let ghciLibByDefault =
         case compilerId comp of
           CompilerId GHC _ ->
@@ -801,10 +795,10 @@ configure (pkg_descr0, pbi) cfg = do
 
   withGHCiLib_ <-
     case fromFlagOrDefault ghciLibByDefault (configGHCiLib cfg) of
-      True | not compilerSupportsGhciLibs -> do
+      True | not linkerSupportsGhciLibs -> do
         warn verbosity $
-          "--enable-library-for-ghci is no longer supported on Windows with"
-            ++ " GHC 9.4 and later; ignoring..."
+          "--enable-library-for-ghci is not supported with the current"
+            ++ "  linker; ignoring..."
         return False
       v -> return v
 
diff --git a/Cabal/src/Distribution/Simple/Program/Db.hs b/Cabal/src/Distribution/Simple/Program/Db.hs
index 5bef94e4b5f..1407230b93b 100644
--- a/Cabal/src/Distribution/Simple/Program/Db.hs
+++ b/Cabal/src/Distribution/Simple/Program/Db.hs
@@ -46,6 +46,7 @@ module Distribution.Simple.Program.Db
   , userSpecifyArgss
   , userSpecifiedArgs
   , lookupProgram
+  , lookupProgramByName
   , updateProgram
   , configuredPrograms
 
@@ -299,7 +300,11 @@ userSpecifiedArgs prog =
 
 -- | Try to find a configured program
 lookupProgram :: Program -> ProgramDb -> Maybe ConfiguredProgram
-lookupProgram prog = Map.lookup (programName prog) . configuredProgs
+lookupProgram = lookupProgramByName . programName
+
+-- | Try to find a configured program
+lookupProgramByName :: String -> ProgramDb -> Maybe ConfiguredProgram
+lookupProgramByName name = Map.lookup name . configuredProgs
 
 -- | Update a configured program in the database.
 updateProgram
diff --git a/changelog.d/pr-9443 b/changelog.d/pr-9443
new file mode 100644
index 00000000000..9a43d9e87e1
--- /dev/null
+++ b/changelog.d/pr-9443
@@ -0,0 +1,12 @@
+synopsis: Use linker capability detection to improve linker use
+packages: Cabal
+prs: #9443
+significance: subtle
+
+description: {
+
+- Previously the GHC version number and platform we used as a proxy for whether
+  the linker can generate relocatable objects.
+- Now, the ability of the linker to create relocatable objects is detected.
+
+}