document IWYU analysis custom build target

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.. _iwyu_processing:

Report missing and unneeded '#include' statements

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The conventions for how and when to use and order include statements in

LAMMPS are `documented in a separate file <https://github.com/lammps/lammps/blob/master/doc/include-file-conventions.md>`_

(also included in the source code distribution).  To assist with following

these conventions one can use the `Include What You Use tool <https://include-what-you-use.org/>`_.

This is still under development and for large and complex projects like LAMMPS

there are some false positives, so suggested changes need to be verified manually.

It is recommended to use at least version 0.14, which has much fewer incorrect

reports than earlier versions.

The necessary steps to generate the report can be enabled via a

CMake variable:

.. code-block:: bash

   -D ENABLE_IWYU=value    # value = no (default) or yes

This will check if the required binary (include-what-you-use or iwyu)

and python script script (iwyu-tool or iwyu_tool or iwyu_tool.py) can

be found in the path.  The analysis can then be started with:

.. code-block:: bash

   make iwyu

This may first run some compilation, as the analysis is dependent

on recording all commands required to do the compilation.

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.. _sanitizer:

Address, Undefined Behavior, and Thread Sanitizer Support