Backport rewrite of the community section

community/contributing/cpp_usage_guidelines.rst

@@ -0,0 +1,100 @@
+.. _doc_cpp_usage_guidelines:
+
+C++ usage guidelines
+====================
+
+Rationale
+---------
+
+Since Godot 4.0, the C++ standard used throughout the codebase is a subset of
+**C++17**. While modern C++ brings a lot of opportunities to write faster, more
+readable code, we chose to restrict our usage of C++ to a subset for a few
+reasons:
+
+- It makes it easier to review code in online editors. This is because engine
+  contributors don't always have access to a full-featured IDE while reviewing
+  code.
+- It makes the code easier to grasp for beginner contributors (who may not be
+  professional C++ programmers). Godot's codebase is known to be easy to learn
+  from, and we'd like to keep it that way.
+
+To get your pull request merged, it needs to follow the C++ usage guidelines
+outlined here. Of course, you can use features not allowed here in your own C++
+modules or GDNative scripts.
+
+.. note::
+
+    Prior to Godot 4.0, the C++ standard used throughout the codebase was C++03,
+    with a handful of C++14 extensions. If you are contributing a pull request
+    to the `3.x` branch rather than `master`, your code can't use C++17 features.
+    Instead, your code must be able to be built with a C++14 compiler.
+
+    The guidelines below don't apply to third-party dependencies, although we
+    generally favor small libraries instead of larger solutions. See also
+    :ref:`doc_best_practices_for_engine_contributors`.
+
+.. seealso::
+
+    See :ref:`doc_code_style_guidelines` for formatting guidelines.
+
+Disallowed features
+-------------------
+
+**Any feature not listed below is allowed.** Using features like ``constexpr``
+variables and ``nullptr`` is encouraged when possible. Still, try to keep your
+use of modern C++ features conservative. Their use needs to serve a real
+purpose, such as improving code readability or performance.
+
+Standard Template Library
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+We don't allow using the `STL <https://en.wikipedia.org/wiki/Standard_Template_Library>`__
+as Godot provides its own data types (among other things).
+See :ref:`doc_faq_why_not_stl` for more information.
+
+This means that pull requests should **not** use ``std::string``,
+``std::vector`` and the like. Instead, use Godot's datatypes as described below:
+
+- Use ``String`` instead of ``std::string``.
+- Use ``Vector`` instead of ``std::vector``. In some cases, ``List`` or
+  ``LocalVector`` can be used as an alternative (ask core developers first).
+- Use ``Array`` instead of ``std::array``.
+
+``auto`` keyword
+^^^^^^^^^^^^^^^^
+
+Please don't use the ``auto`` keyword for type inference. While it can avoid
+repetition, it can also lead to confusing code:
+
+.. code-block:: cpp
+
+    // Not so confusing...
+    auto button = memnew(Button);
+
+    // ...but what about this?
+    auto result = EditorNode::get_singleton()->get_complex_result();
+
+Keep in mind hover documentation often isn't readily available for pull request
+reviewers. Most of the time, reviewers will use GitHub's online viewer to review
+pull requests.
+
+We chose to forbid ``auto`` instead of allowing it on a case-by-case basis to
+avoid having to decide on difficult edge cases. Thank you for your understanding.
+
+Lambdas
+^^^^^^^
+
+Lambdas should be used conservatively when they make code effectively faster or
+simpler, and do not impede readability. Please ask before using lambdas in a
+pull request.
+
+``#pragma once`` directive
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+To follow the existing style, please use standard ``#ifdef``-based include
+guards instead of ``#pragma once`` in new files.
+
+.. seealso::
+
+    See :ref:`doc_code_style_guidelines_header_includes` for guidelines on sorting
+    includes in C++ and Objective-C files.