[CustomOp]Add cpp_extension en doc (#31187)

* add cpp_extension en doc

* remove cuda_cflags and add optional in doc

* refine style

* fix indent problem

* add default None

python/paddle/fluid/tests/custom_op/test_dispatch_jit.py

@@ -32,7 +32,6 @@ dispatch_op = load(
     sources=['dispatch_test_op.cc'],
     extra_include_paths=paddle_includes,  # add for Coverage CI
     extra_cxx_cflags=extra_compile_args,
-    extra_cuda_cflags=extra_compile_args,  # add for Coverage CI
     verbose=True)
 
 

python/paddle/fluid/tests/custom_op/test_multi_out_jit.py

@@ -36,7 +36,6 @@ multi_out_module = load(
     sources=['multi_out_test_op.cc'],
     extra_include_paths=paddle_includes,  # add for Coverage CI
     extra_cxx_cflags=extra_compile_args,  # add for Coverage CI
-    extra_cuda_cflags=extra_compile_args,  # add for Coverage CI
     verbose=True)
 
 

python/paddle/utils/cpp_extension/__init__.py

@@ -25,6 +25,5 @@ from . import cpp_extension
 from . import extension_utils
 
 __all__ = [
-    'CppExtension', 'CUDAExtension', 'BuildExtension', 'load', 'setup',
-    'get_build_directory'
+    'CppExtension', 'CUDAExtension', 'load', 'setup', 'get_build_directory'
 ]

python/paddle/utils/cpp_extension/extension_utils.py

@@ -440,7 +440,22 @@ def is_cuda_file(path):
 
 def get_build_directory(verbose=False):
     """
-    Return paddle extension root directory, default specific by `PADDLE_EXTENSION_DIR`
+    Return paddle extension root directory to put shared library. It could be specified by
+    ``export PADDLE_EXTENSION_DIR=XXX`` . If not set, ``~/.cache/paddle_extension`` will be used
+    by default.
+
+    Returns:
+        The root directory of compiling customized operators.
+
+    Examples:
+
+    .. code-block:: python
+
+        from paddle.utils.cpp_extension import get_build_directory
+
+        build_dir = get_build_directory()
+        print(build_dir)
+
     """
     root_extensions_directory = os.environ.get('PADDLE_EXTENSION_DIR')
     if root_extensions_directory is None: