[zig/nix] fixes for macOS

zig/derivation.nix

@@ -2,6 +2,8 @@
   pkgs,
   stdenv,
   lib,
+  darwin,
+  libiconv,
   zig,
   pkg-config,
   SDL2,
@@ -38,6 +40,13 @@ let
       done;
     '';
   };
+
+  # `apple_sdk` defaults to `10_12` instead of `11_0` on `x86_64-darwin` but we
+  # need `CoreHaptics` to successfully link against `SDL2` and `CoreHaptics` is
+  # not available in `10_12`.
+  #
+  # So, we use `11_0`, even on x86_64.
+  inherit (darwin.apple_sdk_11_0) frameworks;
 in
 
 stdenv.mkDerivation rec {
@@ -48,9 +57,12 @@ stdenv.mkDerivation rec {
     devTools = [ zig ];
   };
 
-  buildInputs = []
-    ++ lib.optional (!stdenv.isDarwin) SDL2
-    ++ lib.optional stdenv.isDarwin SDL2-lowercase
+  buildInputs = [(if stdenv.isDarwin then SDL2-lowercase else SDL2)]
+    ++ lib.optionals stdenv.isDarwin (with frameworks; [
+      IOKit GameController CoreAudio AudioToolbox QuartzCore Carbon Metal
+      Cocoa ForceFeedback CoreHaptics
+    ])
+    ++ lib.optional stdenv.isDarwin libiconv
     ;
 
   nativeBuildInputs = [ zig pkg-config ]
@@ -60,6 +72,33 @@ stdenv.mkDerivation rec {
   dontConfigure = true;
   dontBuild = true;
 
+  # Unforunately `zig`'s parsing of `NIX_LDFLAGS` bails when it encounters any
+  # flags it does not expect.
+  # https://github.com/ziglang/zig/blob/fe6dcdba1407f00584725318404814571cdbd828/lib/std/zig/system/NativePaths.zig#L79
+  #
+  # When `zig` sees the `-liconv` flag that's in `NIX_LDFLAGS` on macOS, it
+  # bails, causing it to miss the `-L` path for SDL.
+  #
+  # Really, this should be fixed in upstream (zig) but for now we just strip out
+  # the `-l` flags:
+  preInstall = ''
+    readonly ORIGINAL_NIX_LDFLAGS=($NIX_LDFLAGS)
+
+    NIX_LDFLAGS=""
+    for c in "''${ORIGINAL_NIX_LDFLAGS[@]}"; do
+      # brittle, bad, etc; this presumes `-l...` style args (no space)
+      if [[ $c =~ ^-l.* ]]; then
+        echo "dropping link flag: $c"
+        continue
+      else
+        echo "keeping link flag: $c"
+        NIX_LDFLAGS="$NIX_LDFLAGS $c"
+      fi
+    done
+
+    export NIX_LDFLAGS
+  '';
+
   ZIG_FLAGS = []
     ++ lib.optional fastSupport "-Doptimize=ReleaseFast"
     ++ lib.optional safeSupport "-Doptimize=ReleaseSafe"