Brad King fa7b041eca PCH: Fix logic error that incorrectly clears sources during VS generation
Since commit 729d997f10 (Precompile Headers: Add REUSE_FROM signature,
2019-08-30, v3.16.0-rc1~101^2), `GetPchFileObject` handles the case that
it is called first for another target's `REUSE_FROM` by calling
`AddSource` to make sure `GetObjectName` can produce the correct object
name.  However, `AddSource` causes `ClearSourcesCache` to be called,
which since commit a9f4f58f0c (cmGeneratorTarget: Clear AllConfigSources
in ClearSourcesCache, 2020-05-15, v3.16.7~2^2) now correctly erases the
`AllConfigSources` structure.  This is okay during `AddPchDependencies`,
but there is another code path in which it is problematic.

When the Visual Studio generator's `WriteAllSources` method is looping
over the sources, the `cmake_pch.cxx` source is encountered first.  This
causes `OutputSourceSpecificFlags` to call `GetPchCreateCompileOptions`,
which calls `GetPchFile`, which under MSVC with `CMAKE_LINK_PCH` calls
`GetPchFileObject`.  That leads to `ClearSourcesCache` erasing the
structure over which `WriteAllSources` is iterating!

This bug is caught by our `RunCMake.PrecompileHeaders` test when run
with the VS generator as of the commit that exposed it by fixing
`ClearSourcesCache`.  However, that change was backported to the CMake
3.16 series after testing only with later versions versions that contain
commit a55df20499 (Multi-Ninja: Add precompile headers support,
2020-01-10, v3.17.0-rc1~136^2).  By adding proper multi-config support
for PCH, that commit taught `cmLocalGenerator::AddPchDependencies` to
call `GetPchFile` with the real set of configurations instead of just
the empty string.  This allows the `GetPchFile` cache of PCH sources to
be populated up front so that the later calls to it in the
`WriteAllSources` loop as described above do not actually call
`GetPchFileObject` or `ClearSourcesCache`.  That hid the problem.

Fix this by re-ordering calls to `AddPchDependencies` to handle
`REUSE_FROM` targets only after the targets whose PCH they re-use.
Remove the now-unnecessary call to `AddSource` from `GetPchFileObject`
so that `ClearSourcesCache` is never called during `WriteAllSources`.
Update the PchReuseFrom test case to cover an ordering of targets that
causes generators to encounter a `REUSE_FROM` target before the target
whose PCH it re-uses.

Fixes: #20770
2020-05-29 05:52:03 -04:00
2019-12-05 14:24:34 -05:00

CMake
*****

Introduction
============

CMake is a cross-platform, open-source build system generator.
For full documentation visit the `CMake Home Page`_ and the
`CMake Documentation Page`_. The `CMake Community Wiki`_ also
references useful guides and recipes.

.. _`CMake Home Page`: https://cmake.org
.. _`CMake Documentation Page`: https://cmake.org/documentation
.. _`CMake Community Wiki`: https://gitlab.kitware.com/cmake/community/wikis/home

CMake is maintained and supported by `Kitware`_ and developed in
collaboration with a productive community of contributors.

.. _`Kitware`: http://www.kitware.com/cmake

License
=======

CMake is distributed under the OSI-approved BSD 3-clause License.
See `Copyright.txt`_ for details.

.. _`Copyright.txt`: Copyright.txt

Building CMake
==============

Supported Platforms
-------------------

* Microsoft Windows
* Apple macOS
* Linux
* FreeBSD
* OpenBSD
* Solaris
* AIX

Other UNIX-like operating systems may work too out of the box, if not
it should not be a major problem to port CMake to this platform.
Please post to the `CMake Discourse Forum`_ to ask if others have
had experience with the platform.

.. _`CMake Discourse Forum`: https://discourse.cmake.org

Building CMake from Scratch
---------------------------

UNIX/Mac OSX/MinGW/MSYS/Cygwin
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You need to have a C++ compiler (supporting C++11) and a ``make`` installed.
Run the ``bootstrap`` script you find in the source directory of CMake.
You can use the ``--help`` option to see the supported options.
You may use the ``--prefix=<install_prefix>`` option to specify a custom
installation directory for CMake.  Once this has finished successfully,
run ``make`` and ``make install``.

For example, if you simply want to build and install CMake from source,
you can build directly in the source tree::

  $ ./bootstrap && make && sudo make install

Or, if you plan to develop CMake or otherwise run the test suite, create
a separate build tree::

  $ mkdir cmake-build && cd cmake-build
  $ ../cmake-source/bootstrap && make

Windows
^^^^^^^

There are two ways for building CMake under Windows:

1. Compile with MSVC from VS 2015 or later.
   You need to download and install a binary release of CMake.  You can get
   these releases from the `CMake Download Page`_.  Then proceed with the
   instructions below for `Building CMake with CMake`_.

2. Bootstrap with MinGW under MSYS2.
   Download and install `MSYS2`_.  Then install the required build tools::

     $ pacman -S --needed git base-devel mingw-w64-x86_64-gcc

   and bootstrap as above.

.. _`CMake Download Page`: https://cmake.org/download
.. _`MSYS2`: https://www.msys2.org/

Building CMake with CMake
-------------------------

You can build CMake as any other project with a CMake-based build system:
run the installed CMake on the sources of this CMake with your preferred
options and generators. Then build it and install it.
For instructions how to do this, see documentation on `Running CMake`_.

.. _`Running CMake`: https://cmake.org/runningcmake

To build the documentation, install `Sphinx`_ and configure CMake with
``-DSPHINX_HTML=ON`` and/or ``-DSPHINX_MAN=ON`` to enable the "html" or
"man" builder.  Add ``-DSPHINX_EXECUTABLE=/path/to/sphinx-build`` if the
tool is not found automatically.

.. _`Sphinx`: http://sphinx-doc.org

Reporting Bugs
==============

If you have found a bug:

1. If you have a patch, please read the `CONTRIBUTING.rst`_ document.

2. Otherwise, please post to the `CMake Discourse Forum`_ and ask about
   the expected and observed behaviors to determine if it is really
   a bug.

3. Finally, if the issue is not resolved by the above steps, open
   an entry in the `CMake Issue Tracker`_.

.. _`CMake Issue Tracker`: https://gitlab.kitware.com/cmake/cmake/issues

Contributing
============

See `CONTRIBUTING.rst`_ for instructions to contribute.

.. _`CONTRIBUTING.rst`: CONTRIBUTING.rst
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