Update build commands for Linux / OS X in the docs (#907)

Author: aldanor

docs/basics.rst

@@ -73,6 +73,8 @@ For brevity, all code examples assume that the following two lines are present:
 
 Some features may require additional headers, but those will be specified as needed.
 
+.. _simple_example:
+
 Creating bindings for a simple function
 =======================================
 
@@ -120,23 +122,31 @@ generates binding code that exposes the ``add()`` function to Python.
     approach and the used syntax are borrowed from Boost.Python, though the
     underlying implementation is very different.
 
-pybind11 is a header-only-library, hence it is not necessary to link against
-any special libraries (other than Python itself). On Windows, use the CMake
-build file discussed in section :ref:`cmake`. On Linux and Mac OS, the above
-example can be compiled using the following command
+pybind11 is a header-only library, hence it is not necessary to link against
+any special libraries and there are no intermediate (magic) translation steps.
+On Linux, the above example can be compiled using the following command:
 
 .. code-block:: bash
 
-    $ c++ -O3 -shared -std=c++11 -I <path-to-pybind11>/include `python-config --cflags --ldflags` example.cpp -o example.so
+    $ c++ -O3 -Wall -shared -std=c++11 -fPIC `python3 -m pybind11 --includes` example.cpp -o example`python3-config --extension-suffix`
+
+For more details on the required compiler flags on Linux and MacOS, see
+:ref:`building_manually`. For complete cross-platform compilation instructions,
+refer to the :ref:`compiling` page.
+
+The `python_example`_ and `cmake_example`_ repositories are also a good place
+to start. They are both complete project examples with cross-platform build
+systems. The only difference between the two is that `python_example`_ uses
+Python's ``setuptools`` to build the module, while `cmake_example`_ uses CMake
+(which may be preferable for existing C++ projects).
 
-In general, it is advisable to include several additional build parameters
-that can considerably reduce the size of the created binary. Refer to section
-:ref:`cmake` for a detailed example of a suitable cross-platform CMake-based
-build system.
+.. _python_example: https://github.com/pybind/python_example
+.. _cmake_example: https://github.com/pybind/cmake_example
 
-Assuming that the created file :file:`example.so` (:file:`example.pyd` on Windows)
-is located in the current directory, the following interactive Python session
-shows how to load and execute the example.
+Building the above C++ code will produce a binary module file that can be
+imported to Python. Assuming that the compiled module is located in the
+current directory, the following interactive Python session shows how to
+load and execute the example:
 
 .. code-block:: pycon
 

docs/compiling.rst

@@ -1,3 +1,5 @@
+.. _compiling:
+
 Build systems
 #############
 
@@ -207,6 +209,59 @@ information about usage in C++, see :doc:`/advanced/embedding`.
     add_executable(example main.cpp)
     target_link_libraries(example PRIVATE pybind11::embed)
 
+.. _building_manually:
+
+Building manually
+=================
+
+pybind11 is a header-only library, hence it is not necessary to link against
+any special libraries and there are no intermediate (magic) translation steps.
+
+On Linux, you can compile an example such as the one given in
+:ref:`simple_example` using the following command:
+
+.. code-block:: bash
+
+    $ c++ -O3 -Wall -shared -std=c++11 -fPIC `python3 -m pybind11 --includes` example.cpp -o example`python3-config --extension-suffix`
+
+The flags given here assume that you're using Python 3. For Python 2, just
+change the executable appropriately (to ``python`` or ``python2``).
+
+The ``python3 -m pybind11 --includes`` command fetches the include paths for
+both pybind11 and Python headers. This assumes that pybind11 has been installed
+using ``pip`` or ``conda``. If it hasn't, you can also manually specify
+``-I <path-to-pybind11>/include`` together with the Python includes path
+``python3-config --includes``.
+
+Note that Python 2.7 modules don't use a special suffix, so you should simply
+use ``example.so`` instead of ``example`python3-config --extension-suffix```.
+Besides, the ``--extension-suffix`` option may or may not be available, depending
+on the distribution; in the latter case, the module extension can be manually
+set to ``.so``.
+
+On Mac OS: the build command is almost the same but it also requires passing
+the ``-undefined dynamic_lookup`` flag so as to ignore missing symbols when
+building the module:
+
+.. code-block:: bash
+
+    $ c++ -O3 -Wall -shared -std=c++11 -undefined dynamic_lookup `python3 -m pybind11 --includes` example.cpp -o example`python3-config --extension-suffix`
+
+In general, it is advisable to include several additional build parameters
+that can considerably reduce the size of the created binary. Refer to section
+:ref:`cmake` for a detailed example of a suitable cross-platform CMake-based
+build system that works on all platforms including Windows.
+
+.. note::
+
+    On Linux and macOS, it's better to (intentionally) not link against
+    ``libpython``. The symbols will be resolved when the extension library
+    is loaded into a Python binary. This is preferable because you might
+    have several different installations of a given Python version (e.g. the
+    system-provided Python, and one that ships with a piece of commercial
+    software). In this way, the plugin will work with both versions, instead
+    of possibly importing a second Python library into a process that already
+    contains one (which will lead to a segfault).
 
 Generating binding code automatically
 =====================================