Linker/darwin: Properly honour -fno-use-rpathswip/t20004

The specification is now simple

* On linux, use `-Xlinker -rpath -Xlinker` to set the rpath of the
executable
* On darwin, never use `-Xlinker -rpath -Xlinker`, always inject
the rpath afterwards, see `runInjectRPaths`.
* If `-fno-use-rpaths` is passed then *never* inject anything into the
rpath.

Fixes #20004

7 files changed, 56 insertions, 32 deletions

diff --git a/compiler/GHC/Driver/Session.hs b/compiler/GHC/Driver/Session.hs
index aa761325d3..fd9efaaafb 100644
--- a/compiler/GHC/Driver/Session.hs
+++ b/compiler/GHC/Driver/Session.hs
@@ -206,6 +206,7 @@ module GHC.Driver.Session (
         -- * Linker/compiler information
         LinkerInfo(..),
         CompilerInfo(..),
+        useXLinkerRPath,
 
         -- * Include specifications
         IncludeSpecs(..), addGlobalInclude, addQuoteInclude, flattenIncludes,
@@ -3680,7 +3681,8 @@ defaultFlags settings
       Opt_ProfCountEntries,
       Opt_SharedImplib,
       Opt_SimplPreInlining,
-      Opt_VersionMacros
+      Opt_VersionMacros,
+      Opt_RPath
     ]
 
     ++ [f | (ns,f) <- optLevelFlags, 0 `elem` ns]
@@ -3688,8 +3690,6 @@ defaultFlags settings
 
     ++ default_PIC platform
 
-    ++ default_RPath platform
-
     ++ validHoleFitDefaults
 
     where platform = sTargetPlatform settings
@@ -3743,29 +3743,6 @@ default_PIC platform =
                                          -- information.
     _                      -> []
 
-
--- We usually want to use RPath, except on macOS (OSDarwin).  On recent macOS
--- versions the number of load commands we can embed in a dynamic library is
--- restricted.  Hence since b592bd98ff2 we rely on -dead_strip_dylib to only
--- link the needed dylibs instead of linking the full dependency closure.
---
--- If we split the library linking into injecting -rpath and -l @rpath/...
--- components, we will reduce the number of libraries we link, however we will
--- still inject one -rpath entry for each library, independent of their use.
--- That is, we even inject -rpath values for libraries that we dead_strip in
--- the end. As such we can run afoul of the load command size limit simply
--- by polluting the load commands with RPATH entries.
---
--- Thus, we disable Opt_RPath by default on OSDarwin.  The savvy user can always
--- enable it with -use-rpath if they so wish.
---
--- See Note [Dynamic linking on macOS]
-
-default_RPath :: Platform -> [GeneralFlag]
-default_RPath platform | platformOS platform == OSDarwin = []
-default_RPath _                                          = [Opt_RPath]
-
-
 -- General flags that are switched on/off when other general flags are switched
 -- on
 impliedGFlags :: [(GeneralFlag, TurnOnFlag, GeneralFlag)]
@@ -4785,6 +4762,40 @@ data CompilerInfo
    | UnknownCC
    deriving Eq
 
+
+-- | Should we use `-XLinker -rpath` when linking or not?
+-- See Note [-fno-use-rpaths]
+useXLinkerRPath :: DynFlags -> OS -> Bool
+useXLinkerRPath _ OSDarwin = False -- See Note [Dynamic linking on macOS]
+useXLinkerRPath dflags _ = gopt Opt_RPath dflags
+
+{-
+Note [-fno-use-rpaths]
+~~~~~~~~~~~~~~~~~~~~~~
+
+First read, Note [Dynamic linking on macOS] to understand why on darwin we never
+use `-XLinker -rpath`.
+
+The specification of `Opt_RPath` is as follows:
+
+The default case `-fuse-rpaths`:
+* On darwin, never use `-Xlinker -rpath -Xlinker`, always inject the rpath
+  afterwards, see `runInjectRPaths`. There is no way to use `-Xlinker` on darwin
+  as things stand but it wasn't documented in the user guide before this patch how
+  `-fuse-rpaths` should behave and the fact it was always disabled on darwin.
+* Otherwise, use `-Xlinker -rpath -Xlinker` to set the rpath of the executable,
+  this is the normal way you should set the rpath.
+
+The case of `-fno-use-rpaths`
+* Never inject anything into the rpath.
+
+When this was first implemented, `Opt_RPath` was disabled on darwin, but
+the rpath was still always augmented by `runInjectRPaths`, and there was no way to
+stop this. This was problematic because you couldn't build an executable in CI
+with a clean rpath.
+
+-}
+
 -- -----------------------------------------------------------------------------
 -- RTS hooks
 
diff --git a/compiler/GHC/Linker/Dynamic.hs b/compiler/GHC/Linker/Dynamic.hs
index 5c96eb55aa..48c3c6fcbd 100644
--- a/compiler/GHC/Linker/Dynamic.hs
+++ b/compiler/GHC/Linker/Dynamic.hs
@@ -57,7 +57,7 @@ linkDynLib logger tmpfs dflags0 unit_env o_files dep_packages
          , -- Only if we want dynamic libraries
            WayDyn `Set.member` ways dflags
            -- Only use RPath if we explicitly asked for it
-         , gopt Opt_RPath dflags
+         , useXLinkerRPath dflags os
             = ["-L" ++ l, "-Xlinker", "-rpath", "-Xlinker", l]
               -- See Note [-Xlinker -rpath vs -Wl,-rpath]
          | otherwise = ["-L" ++ l]
diff --git a/compiler/GHC/Linker/Loader.hs b/compiler/GHC/Linker/Loader.hs
index 97cfac3a7e..749c8ea725 100644
--- a/compiler/GHC/Linker/Loader.hs
+++ b/compiler/GHC/Linker/Loader.hs
@@ -964,7 +964,7 @@ dynLoadObjs interp hsc_env pls@LoaderState{..} objs = do
                            concatMap (\l -> [ Option ("-l" ++ l) ])
                                      (nub $ snd <$> temp_sos)
                         ++ concatMap (\lp -> Option ("-L" ++ lp)
-                                          : if gopt Opt_RPath dflags
+                                          : if useXLinkerRPath dflags (platformOS platform)
                                             then [ Option "-Xlinker"
                                                  , Option "-rpath"
                                                  , Option "-Xlinker"
@@ -973,7 +973,7 @@ dynLoadObjs interp hsc_env pls@LoaderState{..} objs = do
                                      (nub $ fst <$> temp_sos)
                         ++ concatMap
                              (\lp -> Option ("-L" ++ lp)
-                                  : if gopt Opt_RPath dflags
+                                  : if useXLinkerRPath dflags (platformOS platform)
                                     then [ Option "-Xlinker"
                                          , Option "-rpath"
                                          , Option "-Xlinker"
diff --git a/compiler/GHC/Linker/MacOS.hs b/compiler/GHC/Linker/MacOS.hs
index 4851ae96b9..765ea7a7b3 100644
--- a/compiler/GHC/Linker/MacOS.hs
+++ b/compiler/GHC/Linker/MacOS.hs
@@ -44,6 +44,8 @@ import System.FilePath ((</>), (<.>))
 --
 -- See Note [Dynamic linking on macOS]
 runInjectRPaths :: Logger -> DynFlags -> [FilePath] -> FilePath -> IO ()
+-- Make sure to honour -fno-use-rpaths if set on darwin as well see #20004
+runInjectRPaths _ dflags _ _ | not (gopt Opt_RPath dflags) = return ()
 runInjectRPaths logger dflags lib_paths dylib = do
   info <- lines <$> askOtool logger dflags Nothing [Option "-L", Option dylib]
   -- filter the output for only the libraries. And then drop the @rpath prefix.
diff --git a/compiler/GHC/Linker/Static.hs b/compiler/GHC/Linker/Static.hs
index b0b8f1c541..a94fa153f6 100644
--- a/compiler/GHC/Linker/Static.hs
+++ b/compiler/GHC/Linker/Static.hs
@@ -95,7 +95,7 @@ linkBinary' staticLink logger tmpfs dflags unit_env o_files dep_units = do
                                  (l `makeRelativeTo` full_output_fn)
                             else l
                   -- See Note [-Xlinker -rpath vs -Wl,-rpath]
-                  rpath = if gopt Opt_RPath dflags
+                  rpath = if useXLinkerRPath dflags (platformOS platform)
                           then ["-Xlinker", "-rpath", "-Xlinker", libpath]
                           else []
                   -- Solaris 11's linker does not support -rpath-link option. It silently
diff --git a/docs/users_guide/expected-undocumented-flags.txt b/docs/users_guide/expected-undocumented-flags.txt
index f7e55fa573..9861386d0c 100644
--- a/docs/users_guide/expected-undocumented-flags.txt
+++ b/docs/users_guide/expected-undocumented-flags.txt
@@ -82,7 +82,6 @@
 -fspecialize-aggressively
 -fth
 -ftype-function-depth
--fuse-rpaths
 -fversion-macros
 -fvia-c
 -haddock-opts
diff --git a/docs/users_guide/phases.rst b/docs/users_guide/phases.rst
index 73d9777f99..6833ce36d7 100644
--- a/docs/users_guide/phases.rst
+++ b/docs/users_guide/phases.rst
@@ -824,6 +824,18 @@ for example).
     Where to find user-supplied libraries… Prepend the directory ⟨dir⟩
     to the library directories path.
 
+.. ghc-flag:: -fuse-rpaths
+    :shortdesc: Set the rpath based on -L flags
+    :type: dynamic
+    :category: linking
+
+    This flag is enabled by default and will set the rpath of the linked
+    object to the library directories of dependent packages.
+
+    When building binaries to distribute it can be useful to pass your own
+    linker options to control the rpath and disable the automatic injection of
+    rpath entries by disabling this flag.
+
 .. ghc-flag:: -framework-path ⟨dir⟩
     :shortdesc: On Darwin/OS X/iOS only, add ⟨dir⟩ to the list of directories
         searched for frameworks. This option corresponds to the ``-F``
@@ -911,7 +923,7 @@ for example).
     When linking shared libraries (:ghc-flag:`-shared`) GHC does not
     automatically link the RTS.  This is to allow choosing the RTS flavour
     (:ghc-flag:`-threaded`, :ghc-flag:`-eventlog`, etc) when linking an
-    executable. 
+    executable.
     However when the shared library is the intended product it is useful to be
     able to reverse this default. See :ref:`shared-libraries-c-api` for an
     usage example.