Work around otool not set to nix store path in GHC settings

In previous GHC versions from nixpkgs, the `otool` setting was referencing a tool in the nix store,
but for GHC 9.6.2 it is just set to "otool" which means it must be in `$PATH`.

The same applies to the `install_name_tool`.

See NixOS/nixpkgs#267250 and https://gitlab.haskell.org/ghc/ghc/-/issues/24211

We work around by using the location of the `ar` command and assume the other tools (from the bintools
package) are also available at the same place.

haskell/cabal.bzl

@@ -289,6 +289,15 @@ def _prepare_cabal_inputs(
     ]
     extra_args = ["--flags=" + " ".join(flags)]
 
+    if hs.toolchain.is_darwin:
+        # assume `otool` and `install_name_tool` are available at the same location as `ar`
+        ar_bindir = paths.dirname(cc.tools.ar)
+
+        extra_args.append("--ghc-option=-pgmotool=" + paths.join(ar_bindir, "otool"))
+        extra_args.append("--ghc-option=-pgminstall_name_tool=" + paths.join(ar_bindir, "install_name_tool"))
+        extra_args.append("--haddock-option=--optghc=-pgmotool=" + paths.join(ar_bindir, "otool"))
+        extra_args.append("--haddock-option=--optghc=-pgminstall_name_tool=" + paths.join(ar_bindir, "install_name_tool"))
+
     ghc_version = [int(x) for x in hs.toolchain.version.split(".")]
     if dynamic_file:
         # See Note [No PIE when linking] in haskell/private/actions/link.bzl

haskell/experimental/private/module.bzl

@@ -302,6 +302,13 @@ def _build_haskell_module(
     args.add_all(hs.toolchain.ghcopts)
     args.add_all(user_ghcopts)
 
+    if hs.toolchain.is_darwin:
+        # assume `otool` and `install_name_tool` are available at the same location as `ar`
+        ar_bindir = paths.dirname(cc.tools.ar)
+
+        args.add(paths.join(ar_bindir, "otool"), format = "-pgmotool=%s")
+        args.add(paths.join(ar_bindir, "install_name_tool"), format = "-pgminstall_name_tool=%s")
+
     if plugins and not enable_th:
         # For #1681. These suppresses bogus warnings about missing libraries which
         # aren't really needed.

haskell/private/actions/link.bzl

@@ -133,6 +133,14 @@ def link_binary(
     args.add_all(cc.linker_flags, format_each = "-optl%s")
     if with_profiling:
         args.add("-prof")
+
+    if hs.toolchain.is_darwin:
+        # assume `otool` and `install_name_tool` are available at the same location as `ar`
+        ar_bindir = paths.dirname(cc.tools.ar)
+
+        args.add(paths.join(ar_bindir, "otool"), format = "-pgmotool=%s")
+        args.add(paths.join(ar_bindir, "install_name_tool"), format = "-pgminstall_name_tool=%s")
+
     args.add_all(hs.toolchain.ghcopts)
     args.add_all(compiler_flags)
 
@@ -366,6 +374,14 @@ def link_library_dynamic(hs, cc, posix, dep_info, extra_srcs, object_files, my_p
     args = hs.actions.args()
     args.add_all(cc.linker_flags, format_each = "-optl%s")
     args.add_all(["-shared", "-dynamic"])
+
+    if hs.toolchain.is_darwin:
+        # assume `otool` and `install_name_tool` are available at the same location as `ar`
+        ar_bindir = paths.dirname(cc.tools.ar)
+
+        args.add(paths.join(ar_bindir, "otool"), format = "-pgmotool=%s")
+        args.add(paths.join(ar_bindir, "install_name_tool"), format = "-pgminstall_name_tool=%s")
+
     args.add_all(hs.toolchain.ghcopts)
     args.add_all(compiler_flags)