From d424287eeb42eda2bb2e97dccc05797ce900cf7c Mon Sep 17 00:00:00 2001
From: Erik de Castro Lopo <erikd@mega-nerd.com>
Date: Tue, 14 Nov 2023 14:41:24 +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 used the compiler version
as a proxy for whether the linker supports relocatable objects. Now
support for relocatable objects is detected by running it.
---
 Cabal/src/Distribution/Simple/Configure.hs  | 28 ++++++++-------------
 Cabal/src/Distribution/Simple/Program/Db.hs |  7 +++++-
 2 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/Cabal/src/Distribution/Simple/Configure.hs b/Cabal/src/Distribution/Simple/Configure.hs
index 1c9188a2a6b..5289dc64652 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 _ ->
@@ -801,7 +795,7 @@ 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..."
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