v8: fixes build on darwin

v8 compilation on macOS was failing because of missing dependency and
wrong linker. The approach to make it work is similar to the nodejs
package.

pkgs/development/libraries/v8/default.nix

···
 { stdenv, lib, fetchgit, fetchFromGitHub, gyp, readline, python, which, icu
-, patchelf, coreutils
+, patchelf, coreutils, cctools
 , doCheck ? false
 , static ? false
 }:
···
 
   # Patch based off of:
   # https://github.com/cowboyd/libv8/tree/v5.1.281.67.0/patches
-  patches = lib.optional (!doCheck) ./libv8-5.4.232.patch;
+  patches = lib.optional (!doCheck) ./libv8-5.4.232.patch
+  ++ stdenv.lib.optionals stdenv.isDarwin [ ./no-xcode.patch ];
+
+  prePatch = ''
+    chmod +w tools/gyp/pylib/gyp
+    chmod +w tools/gyp/pylib/gyp/xcode_emulation.py
+  '';
 
   postPatch = ''
     sed -i 's,#!/usr/bin/env python,#!${python}/bin/python,' gypfiles/gyp_v8
···
   '';
 
   nativeBuildInputs = [ which ];
-  buildInputs = [ readline python icu patchelf ];
+  buildInputs = [ readline python icu patchelf ]
+  ++ stdenv.lib.optionals stdenv.isDarwin [ cctools ];
 
   NIX_CFLAGS_COMPILE = "-Wno-error=strict-overflow";
 
   buildFlags = [
-    "LINK=g++"
+    "LINK=c++"
     "-C out"
     "builddir=$(CURDIR)/Release"
     "BUILDTYPE=Release"
···
     install -vD out/Release/mksnapshot "$out/bin/mksnapshot"
     ${if static then ""
     else if stdenv.isDarwin then ''
-    install -vD out/Release/lib.target/libv8.dylib "$out/lib/libv8.dylib"
+    install -vD out/Release/libv8.dylib "$out/lib/libv8.dylib"
     install_name_tool -change /usr/local/lib/libv8.dylib $out/lib/libv8.dylib -change /usr/lib/libgcc_s.1.dylib ${stdenv.cc.cc.lib}/lib/libgcc_s.1.dylib $out/bin/d8
     install_name_tool -id $out/lib/libv8.dylib -change /usr/lib/libgcc_s.1.dylib ${stdenv.cc.cc.lib}/lib/libgcc_s.1.dylib $out/lib/libv8.dylib
     '' else ''
···
   meta = with lib; {
     description = "Google's open source JavaScript engine";
     maintainers = with maintainers; [ cstrahan proglodyte ];
-    platforms = platforms.linux;
+    platforms = platforms.linux ++ platforms.darwin;
     license = licenses.bsd3;
   };
 }

pkgs/development/libraries/v8/no-xcode.patch

···
+--- a/tools/gyp/pylib/gyp/xcode_emulation.py
++++ a/tools/gyp/pylib/gyp/xcode_emulation.py
+@@ -473,10 +473,16 @@
+ 
+   def _XcodeSdkPath(self, sdk_root):
+     if sdk_root not in XcodeSettings._sdk_path_cache:
+-      sdk_path = self._GetSdkVersionInfoItem(sdk_root, '--show-sdk-path')
+-      XcodeSettings._sdk_path_cache[sdk_root] = sdk_path
+-      if sdk_root:
+-        XcodeSettings._sdk_root_cache[sdk_path] = sdk_root
++      try:
++        sdk_path = self._GetSdkVersionInfoItem(sdk_root, '--show-sdk-path')
++        XcodeSettings._sdk_path_cache[sdk_root] = sdk_path
++        if sdk_root:
++          XcodeSettings._sdk_root_cache[sdk_path] = sdk_root
++      except:
++        # if this fails it's because xcodebuild failed, which means
++        # the user is probably on a CLT-only system, where there
++        # is no valid SDK root
++        XcodeSettings._sdk_path_cache[sdk_root] = None
+     return XcodeSettings._sdk_path_cache[sdk_root]
+ 
+   def _AppendPlatformVersionMinFlags(self, lst):
+@@ -606,10 +612,11 @@
+       framework_root = sdk_root
+     else:
+       framework_root = ''
+-    config = self.spec['configurations'][self.configname]
+-    framework_dirs = config.get('mac_framework_dirs', [])
+-    for directory in framework_dirs:
+-      cflags.append('-F' + directory.replace('$(SDKROOT)', framework_root))
++    if 'SDKROOT' in self._Settings():
++      config = self.spec['configurations'][self.configname]
++      framework_dirs = config.get('mac_framework_dirs', [])
++      for directory in framework_dirs:
++        cflags.append('-F' + directory.replace('$(SDKROOT)', framework_root))
+ 
+     self.configname = None
+     return cflags
+@@ -861,10 +868,11 @@
+     sdk_root = self._SdkPath()
+     if not sdk_root:
+       sdk_root = ''
+-    config = self.spec['configurations'][self.configname]
+-    framework_dirs = config.get('mac_framework_dirs', [])
+-    for directory in framework_dirs:
+-      ldflags.append('-F' + directory.replace('$(SDKROOT)', sdk_root))
++    if 'SDKROOT' in self._Settings():
++      config = self.spec['configurations'][self.configname]
++      framework_dirs = config.get('mac_framework_dirs', [])
++      for directory in framework_dirs:
++        ldflags.append('-F' + directory.replace('$(SDKROOT)', sdk_root))
+ 
+     platform_root = self._XcodePlatformPath(configname)
+     if sdk_root and platform_root and self._IsXCTest():
+@@ -1358,7 +1366,7 @@
+     if version:
+       version = re.match(r'(\d\.\d\.?\d*)', version).groups()[0]
+     else:
+-      raise GypError("No Xcode or CLT version detected!")
++      version = "7.0.0"
+     # The CLT has no build information, so we return an empty string.
+     version_list = [version, '']
+   version = version_list[0]

pkgs/top-level/all-packages.nix

···
 
   v8 = callPackage ../development/libraries/v8 {
     inherit (python2Packages) python gyp;
+    cctools = darwin.cctools;
   };
 
   v8_static = lowPrio (self.v8.override { static = true; });