Refactors the scons script (by Vlad Losev).

Fixes a typo in __GNUC__ (by Zhanyong Wan).

scons/SConstruct.common

@@ -247,5 +247,114 @@ class SConstructHelper:
                  variant_dir=env['BUILD_DIR'],
                  duplicate=0)
 
+  class EnvCreator:
+    """Creates new customized environments from a base one."""
+
+    def _Remove(cls, env, attribute, value):
+      """Removes the given attribute value from the environment."""
+
+      attribute_values = env[attribute]
+      if value in attribute_values:
+        attribute_values.remove(value)
+    _Remove = classmethod(_Remove)
+
+    def Create(cls, base_env, modifier=None):
+      # User should NOT create more than one environment with the same
+      # modifier (including None).
+      env = base_env.Clone()
+      if modifier:
+        modifier(env)
+      else:
+        env['OBJ_SUFFIX'] = ''  # Default suffix for unchanged environment.
+      return env;
+    Create = classmethod(Create)
+
+    # Each of the following methods modifies the environment for a particular
+    # purpose and can be used by clients for creating new environments.  Each
+    # one needs to set the OBJ_SUFFIX variable to a unique suffix to
+    # differentiate targets built with that environment.  Otherwise, SCons may
+    # complain about same target built with different settings.
+
+    def UseOwnTuple(cls, env):
+      """Instructs Google Test to use its internal implementation of tuple."""
+
+      env['OBJ_SUFFIX'] = '_use_own_tuple'
+      env.Append(CPPDEFINES = 'GTEST_USE_OWN_TR1_TUPLE=1')
+    UseOwnTuple = classmethod(UseOwnTuple)
+
+    def WarningOk(cls, env):
+      """Does not treat warnings as errors.
+
+      Necessary for compiling gtest_unittest.cc, which triggers a gcc
+      warning when testing EXPECT_EQ(NULL, ptr)."""
+
+      env['OBJ_SUFFIX'] = '_warning_ok'
+      if env['PLATFORM'] == 'win32':
+        cls._Remove(env, 'CCFLAGS', '-WX')
+      else:
+        cls._Remove(env, 'CCFLAGS', '-Werror')
+    WarningOk = classmethod(WarningOk)
+
+    def WithExceptions(cls, env):
+      """Re-enables exceptions."""
+
+      # We compile gtest_unittest in this environment which means we need to
+      # allow warnings here as well.
+      cls.WarningOk(env)
+      env['OBJ_SUFFIX'] = '_ex'  # Overrides the suffix supplied by WarningOK.
+      if env['PLATFORM'] == 'win32':
+        env.Append(CCFLAGS=['/EHsc'])
+        env.Append(CPPDEFINES='_HAS_EXCEPTIONS=1')
+        # Undoes the _TYPEINFO_ hack, which is unnecessary and only creates
+        # trouble when exceptions are enabled.
+        cls._Remove(env, 'CPPDEFINES', '_TYPEINFO_')
+        cls._Remove(env, 'CPPDEFINES', '_HAS_EXCEPTIONS=0')
+      else:
+        env.Append(CCFLAGS='-fexceptions')
+        cls._Remove(env, 'CCFLAGS', '-fno-exceptions')
+    WithExceptions = classmethod(WithExceptions)
+
+    def LessOptimized(cls, env):
+      """Disables certain optimizations on Windows.
+
+      We need to disable some optimization flags for some tests on
+      Windows; otherwise the redirection of stdout does not work
+      (apparently because of a compiler bug)."""
+
+      env['OBJ_SUFFIX'] = '_less_optimized'
+      if env['PLATFORM'] == 'win32':
+        for flag in ['/O1', '/Os', '/Og', '/Oy']:
+          cls._Remove(env, 'LINKFLAGS', flag)
+    LessOptimized = classmethod(LessOptimized)
+
+    def WithThreads(cls, env):
+      """Allows use of threads.
+
+      Currently only enables pthreads under GCC."""
+
+      env['OBJ_SUFFIX'] = '_with_threads'
+      if env['PLATFORM'] != 'win32':
+        # Assuming POSIX-like environment with GCC.
+        # TODO(vladl@google.com): sniff presence of pthread_atfork instead of
+        # selecting on a platform.
+        env.Append(CCFLAGS=['-pthread'])
+        env.Append(LINKFLAGS=['-pthread'])
+    WithThreads = classmethod(WithThreads)
+
+    def NoRtti(cls, env):
+      """Disables RTTI support."""
+
+      # We compile gtest_unittest in this environment which means we need to
+      # allow warnings here as well.
+      cls.WarningOk(env)
+      env['OBJ_SUFFIX'] = '_no_rtti'  # Overrides suffix supplied by WarningOK.
+      if env['PLATFORM'] == 'win32':
+        env.Append(CCFLAGS=['/GR-'])
+      else:
+        env.Append(CCFLAGS=['-fno-rtti'])
+        env.Append(CPPDEFINES='GTEST_HAS_RTTI=0')
+    NoRtti = classmethod(NoRtti)
+
+
 sconstruct_helper = SConstructHelper()
 Return('sconstruct_helper')