Check compiler versions at Python setup time

setup.py

@@ -81,15 +81,10 @@ EXTENSION_LIBRARIES = ()
 if not "darwin" in sys.platform:
     EXTENSION_LIBRARIES += ('rt',)
 
-EXTRA_COMPILE_ARGS = ()
-if not "win" in sys.platform:
-  EXTRA_COMPILE_ARGS = ('-pthread',)
-
 DEFINE_MACROS = (('OPENSSL_NO_ASM', 1),)
 
 def cython_extensions(package_names, module_names, include_dirs, libraries,
-                      define_macros, extra_compile_args,
-                      build_with_cython=False):
+                      define_macros, build_with_cython=False):
   if ENABLE_CYTHON_TRACING:
     define_macros = define_macros + [('CYTHON_TRACE_NOGIL', 1)]
   file_extension = 'pyx' if build_with_cython else 'c'
@@ -101,7 +96,6 @@ def cython_extensions(package_names, module_names, include_dirs, libraries,
           name=module_name,
           sources=[module_file] + grpc_core_dependencies.CORE_SOURCE_FILES,
           include_dirs=include_dirs, libraries=libraries,
-          extra_compile_args=extra_compile_args,
           define_macros=define_macros,
       ) for (module_name, module_file) in zip(module_names, module_files)
   ]
@@ -117,7 +111,7 @@ def cython_extensions(package_names, module_names, include_dirs, libraries,
 CYTHON_EXTENSION_MODULES = cython_extensions(
     list(CYTHON_EXTENSION_PACKAGE_NAMES), list(CYTHON_EXTENSION_MODULE_NAMES),
     list(EXTENSION_INCLUDE_DIRECTORIES), list(EXTENSION_LIBRARIES),
-    list(DEFINE_MACROS), list(EXTRA_COMPILE_ARGS), bool(BUILD_WITH_CYTHON))
+    list(DEFINE_MACROS), bool(BUILD_WITH_CYTHON))
 
 PACKAGE_DIRECTORIES = {
     '': PYTHON_STEM,
@@ -137,6 +131,7 @@ COMMAND_CLASS = {
     'build_proto_modules': commands.BuildProtoModules,
     'build_project_metadata': commands.BuildProjectMetadata,
     'build_py': commands.BuildPy,
+    'build_ext': commands.BuildExt,
     'gather': commands.Gather,
     'run_interop': commands.RunInterop,
 }

src/python/grpcio/commands.py

@@ -40,6 +40,17 @@ import setuptools
 from setuptools.command import build_py
 from setuptools.command import test
 
+# Because we need to support building without Cython but simultaneously need to
+# subclass its command class when we need to and because distutils requires a
+# special hook to acquire a command class, we attempt to import Cython's
+# build_ext, and if that fails we import setuptools'.
+try:
+  # Due to the strange way Cython's Distutils module re-imports build_ext, we
+  # import the build_ext class directly.
+  from Cython.Distutils.build_ext import build_ext
+except ImportError:
+  from setuptools.command.build_ext import build_ext
+
 PYTHON_STEM = os.path.dirname(os.path.abspath(__file__))
 
 CONF_PY_ADDENDUM = """
@@ -168,6 +179,26 @@ class BuildPy(build_py.build_py):
     build_py.build_py.run(self)
 
 
+class BuildExt(build_ext):
+  """Custom build_ext command to enable compiler-specific flags."""
+
+  C_OPTIONS = {
+      'unix': ('-pthread', '-std=gnu99'),
+      'msvc': (),
+  }
+  LINK_OPTIONS = {}
+
+  def build_extensions(self):
+    compiler = self.compiler.compiler_type
+    if compiler in BuildExt.C_OPTIONS:
+      for extension in self.extensions:
+        extension.extra_compile_args += list(BuildExt.C_OPTIONS[compiler])
+    if compiler in BuildExt.LINK_OPTIONS:
+      for extension in self.extensions:
+        extension.extra_link_args += list(BuildExt.LINK_OPTIONS[compiler])
+    build_ext.build_extensions(self)
+
+
 class Gather(setuptools.Command):
   """Command to gather project dependencies."""