[Enhancement] Fix collect_env on Windows (#1789)

* [fix] fix collect_env() on Windows

* fix(utils): add back 'Cuda compilation tools' to nvcc info

* feat(utils): find default ccompiler

* fix(utils, test): parse cl.exe version instead of path

* fix: code style

* fix(tools): use distutils

* [fix] collect_env() returns GCC or MSVC

* [fix] unitest for collect_env()

* add comments

* test: add GCC to expected_keys

* fix: code style

* Update mmcv/utils/env.py

mmcv/utils/env.py

@@ -26,6 +26,7 @@ def collect_env():
             - CUDA_HOME (optional): The env var ``CUDA_HOME``.
             - NVCC (optional): NVCC version.
             - GCC: GCC version, "n/a" if GCC is not installed.
+            - MSVC: Microsoft Virtual C++ Compiler version, Windows only.
             - PyTorch: PyTorch version.
             - PyTorch compiling details: The output of \
                 ``torch.__config__.show()``.
@@ -56,18 +57,40 @@ def collect_env():
         if CUDA_HOME is not None and osp.isdir(CUDA_HOME):
             try:
                 nvcc = osp.join(CUDA_HOME, 'bin/nvcc')
-                nvcc = subprocess.check_output(
-                    f'"{nvcc}" -V | tail -n1', shell=True)
+                nvcc = subprocess.check_output(f'"{nvcc}" -V', shell=True)
                 nvcc = nvcc.decode('utf-8').strip()
+                release = nvcc.rfind('Cuda compilation tools')
+                build = nvcc.rfind('Build ')
+                nvcc = nvcc[release:build].strip()
             except subprocess.SubprocessError:
                 nvcc = 'Not Available'
             env_info['NVCC'] = nvcc
 
     try:
-        gcc = subprocess.check_output('gcc --version | head -n1', shell=True)
-        gcc = gcc.decode('utf-8').strip()
-        env_info['GCC'] = gcc
-    except subprocess.CalledProcessError:  # gcc is unavailable
+        # Check C++ Compiler.
+        # For Unix-like, sysconfig has 'CC' variable like 'gcc -pthread ...',
+        # indicating the compiler used, we use this to get the compiler name
+        import sysconfig
+        cc = sysconfig.get_config_var('CC')
+        if cc:
+            cc = osp.basename(cc.split()[0])
+            cc_info = subprocess.check_output(f'{cc} --version', shell=True)
+            env_info['GCC'] = cc_info.decode('utf-8').partition(
+                '\n')[0].strip()
+        else:
+            # on Windows, cl.exe is not in PATH. We need to find the path.
+            # distutils.ccompiler.new_compiler() returns a msvccompiler
+            # object and after initialization, path to cl.exe is found.
+            import locale
+            from distutils.ccompiler import new_compiler
+            ccompiler = new_compiler()
+            ccompiler.initialize()
+            cc = subprocess.check_output(
+                f'{ccompiler.cc}', stderr=subprocess.STDOUT, shell=True)
+            encoding = locale.getdefaultlocale()[1]
+            env_info['MSVC'] = cc.decode(encoding).partition('\n')[0].strip()
+            env_info['GCC'] = 'n/a'
+    except subprocess.CalledProcessError:
         env_info['GCC'] = 'n/a'
 
     env_info['PyTorch'] = torch.__version__

tests/test_utils/test_env.py

@@ -16,7 +16,7 @@ def test_collect_env():
     env_info = collect_env()
     expected_keys = [
         'sys.platform', 'Python', 'CUDA available', 'PyTorch',
-        'PyTorch compiling details', 'OpenCV', 'MMCV', 'MMCV Compiler',
+        'PyTorch compiling details', 'OpenCV', 'MMCV', 'MMCV Compiler', 'GCC',
         'MMCV CUDA Compiler'
     ]
     for key in expected_keys:
@@ -26,8 +26,8 @@ def test_collect_env():
         for key in ['CUDA_HOME', 'NVCC']:
             assert key in env_info
 
-    if sys.platform != 'win32':
-        assert 'GCC' in env_info
+    if sys.platform == 'win32':
+        assert 'MSVC' in env_info
 
     assert env_info['sys.platform'] == sys.platform
     assert env_info['Python'] == sys.version.replace('\n', '')