add a new feature to select the target Android platform.

tasks/toolchains/androideabi.rake

@@ -14,12 +14,15 @@ MRuby::Toolchain.new(:androideabi) do |conf|
   DEFAULT_ANDROID_TOOLCHAIN   = 'gcc'
   DEFAULT_ANDROID_TARGET_ARCH = 'arm'
   DEFAULT_ANDROID_TARGET_ARCH_ABI = 'armeabi'
+  DEFAULT_ANDROID_TARGET_PLATFORM = 'android-14'
+  DEFAULT_GCC_VERSION   = '4.6'
+  DEFAULT_CLANG_VERSION = '3.1'
   GCC_COMMON_CFLAGS  = %W(-ffunction-sections -funwind-tables -fstack-protector)
   GCC_COMMON_LDFLAGS = %W()
 
-  # An environment variable 'ANDROID_STANDALONE_TOOLCHAIN' must be set a path to toolchains.
+  # 'ANDROID_STANDALONE_TOOLCHAIN' or 'ANDROID_NDK_HOME' must be set.
   ANDROID_STANDALONE_TOOLCHAIN = ENV['ANDROID_STANDALONE_TOOLCHAIN']
-  SYSROOT = ENV['ANDROID_STANDALONE_TOOLCHAIN'] + '/sysroot'
+  ANDROID_NDK_HOME = ENV['ANDROID_NDK_HOME']
 
   ANDROID_TARGET_ARCH = ENV['ANDROID_TARGET_ARCH'] || DEFAULT_ANDROID_TARGET_ARCH
   ANDROID_TOOLCHAIN = ENV['ANDROID_TOOLCHAIN'] || DEFAULT_ANDROID_TOOLCHAIN
@@ -36,11 +39,51 @@ MRuby::Toolchain.new(:androideabi) do |conf|
     # Notify error.
   end
 
+  if ANDROID_STANDALONE_TOOLCHAIN == nil then
+    if RUBY_PLATFORM.include?('darwin') then
+      HOST_PLATFORM = 'darwin-x86'
+    elsif RUBY_PLATFORM.include('linux') then
+      HOST_PLATFORM = 'linux-x86'
+    elsif RUBY_PLATFORM.include('win') then
+      HOST_PLATFORM = 'windows'
+    else
+      # Unknown host platform.
+    end
+
+    ANDROID_TARGET_PLATFORM = ENV['ANDROID_TARGET_PLATFORM'] || DEFAULT_ANDROID_TARGET_PLATFORM
+
+    path_to_toolchain = ANDROID_NDK_HOME + '/toolchains/'
+	path_to_sysroot   = ANDROID_NDK_HOME + '/platforms/' + ANDROID_TARGET_PLATFORM
+    if ANDROID_TOOLCHAIN.downcase == 'gcc' then
+      case ANDROID_TARGET_ARCH.downcase
+      when 'arch-arm',  'arm'  then
+        path_to_toolchain += 'arm-linux-androideabi-'
+        path_to_sysroot   += '/arch-arm'
+      when 'arch-x86',  'x86'  then
+        path_to_toolchain += 'x86-'
+        path_to_sysroot   += '/arch-x86'
+      when 'arch-mips', 'mips' then
+        path_to_toolchain += 'mipsel-linux-android-'
+        path_to_sysroot   += '/arch-mips'
+      else
+        # Any other architecture are not supported by Android NDK.
+      end
+      path_to_toolchain += DEFAULT_GCC_VERSION + '/prebuilt/' + HOST_PLATFORM
+    else
+      path_to_toolchain += 'llvm-' + DEFAULT_CLANG_VERSION + '/prebuilt/' + HOST_PLATFORM
+    end
+  else
+    path_to_toolchain = ANDROID_STANDALONE_TOOLCHAIN
+    path_to_sysroot   = ANDROID_STANDALONE_TOOLCHAIN + '/sysroot'
+  end
+
+  SYSROOT = path_to_sysroot
+
   case ANDROID_TOOLCHAIN.downcase
   when 'gcc' then
-    ANDROID_CC = ANDROID_STANDALONE_TOOLCHAIN + '/bin/' + toolchain_prefix + 'gcc'
-    ANDROID_LD = ANDROID_STANDALONE_TOOLCHAIN + '/bin/' + toolchain_prefix + 'gcc'
-    ANDROID_AR = ANDROID_STANDALONE_TOOLCHAIN + '/bin/' + toolchain_prefix + 'ar'
+    ANDROID_CC = path_to_toolchain + '/bin/' + toolchain_prefix + 'gcc'
+    ANDROID_LD = path_to_toolchain + '/bin/' + toolchain_prefix + 'gcc'
+    ANDROID_AR = path_to_toolchain + '/bin/' + toolchain_prefix + 'ar'
     ANDROID_CFLAGS  = GCC_COMMON_CFLAGS + %W(-mandroid --sysroot=#{SYSROOT})
     ANDROID_LDFLAGS = GCC_COMMON_LDFLAGS + %W(-mandroid --sysroot=#{SYSROOT})
   when 'clang' then