Fix develop mode in debug mode

Signed-off-by: Nicolas Castet <26874160+nvcastet@users.noreply.github.com>

docs/contributors.rst

@@ -47,18 +47,13 @@ Set ``HOROVOD_WITHOUT_[FRAMEWORK]=1`` to disable building Horovod plugins for th
 This is useful when you’re testing a feature of one framework in particular and wish to save time.
 Set ``HOROVOD_WITH_[FRAMEWORK]=1`` to generate an error if the Horovod plugin for that framework failed to build.
 Set ``HOROVOD_GPU_OPERATIONS=NCCL`` to run on GPUs with NCCL.
+Set ``HOROVOD_DEBUG=1`` for a debug build with checked assertions, disabled compiler optimizations etc.
 You can install optional dependencies defined in `setup.py <https://github.com/horovod/horovod/blob/master/setup.py>`__ by adding brackets
 at the end of the command line e.g. ``[test]`` for test dependencies.
 
 In develop mode, you can edit the Horovod source directly in the repo folder. For Python code, the changes will take effect
 immediately. For **C++/CUDA code**, the ``... pip install -v -e .`` command needs to be invoked again to perform an incremental build.
 
-For a debug build with debug symbols, checked assertions etc., use the extra flags below:
-
-.. code-block:: bash
-
-    $ HOROVOD_WITH_PYTORCH=1 HOROVOD_WITH_TENSORFLOW=1 pip install --global-option build_ext --global-option --debug -v -e .
-
 Testing
 -------
 

setup.py

@@ -70,7 +70,7 @@ def build_extensions(self):
 
         cmake_bin = get_cmake_bin()
 
-        config = 'Debug' if self.debug else 'RelWithDebInfo'
+        config = 'Debug' if self.debug or os.environ.get('HOROVOD_DEBUG') == "1" else 'RelWithDebInfo'
 
         ext_name = self.extensions[0].name
         build_dir = self.get_ext_fullpath(ext_name).replace(self.get_ext_filename(ext_name), '')