Add note about extension-pkg-whitelist. Close #1962

doc/technical_reference/c_extensions.rst

@@ -0,0 +1,29 @@
+Pylint and C extensions
+=======================
+
+If you are getting the dreaded **no-member** error, there is a possibility that
+either **pylint** found a bug in your code or that it actually tries to lint
+a C extension module.
+
+Linting C extension modules is not supported out of the box, especially since
+pylint has no way to get an AST object out of the extension module.
+
+But **pylint** actually has a mechanism which you might use in case you
+want to analyze C extensions. **pylint** has a flag, called **extension-pkg-whitelist**,
+through which you can tell it to import that module and to build an AST from that
+imported module::
+
+   $ pylint --extension-pkg-whitelist=your_c_extension
+
+Be aware though that using this flag means that extensions are loaded into the
+active Python interpreter and may run arbitrary code, which you may not want. This
+is the reason why we disable by default loading C extensions. In case you do not want
+the hassle of passing C extensions module with this flag all the time, you
+can enable **unsafe-load-any-extension** in your configuration file, which will
+build AST objects from all the C extensions that **pylint** encounters::
+
+   $ pylint --unsafe-load-any-extension=y
+
+Alternatively, since **pylint** emits a separate error for attributes that cannot be
+found in C extensions, **c-extension-no-member**, you can disable this error for
+your project.

doc/technical_reference/index.rst

@@ -17,3 +17,4 @@ Technical Reference
   checkers
   extensions
   features
+  c_extensions