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If multiple ExternalData_Target_Add calls generate the same output file then we need to avoid calling add_custom_command multiple times with that output. This was already done within a single target by setting a variable in the local function scope. This will not be visible in other calls though so we need to use a directory property instead to prevent adding a custom command multiple times for one output in a directory. Normally it is not safe to have multiple custom commands that produce the same output file across multiple independent targets, but since we use atomic replacement of outputs the resulting races should not be a problem. For the convenience of projects, tolerate this instead of diagnosing it. In particular, we previously allowed up to two copies of the custom command in one directory because CMake has a fallback from MAIN_DEPENDENCY to an `<output>.rule` file. While at it, add a note to the documentation that typically only one external data target should be needed for a project. Reported-by: David Manthey <david.manthey@kitware.com>
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`_. .. _`CMake Home Page`: https://cmake.org .. _`CMake Documentation Page`: https://cmake.org/cmake/help/documentation.html 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 ------------------- MS Windows, Mac OS X, Linux, FreeBSD, Solaris, HP-UX, IRIX, BeOS, QNX 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. Subscribe and post to the `CMake Users List`_ to ask if others have had experience with the platform. .. _`CMake Users List`: https://cmake.org/mailman/listinfo/cmake Building CMake from Scratch --------------------------- UNIX/Mac OSX/MinGW/MSYS/Cygwin ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ You need to have a compiler 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. You can run the ``bootstrap`` script from within the CMake source directory or any other build directory of your choice. Once this has finished successfully, run ``make`` and ``make install``. In summary:: $ ./bootstrap && make && make install Windows ^^^^^^^ You need to download and install a binary release of CMake in order to build CMake. You can get these releases from the `CMake Download Page`_ . Then proceed with the instructions below. .. _`CMake Download Page`: https://cmake.org/cmake/resources/software.html 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/cmake/help/runningcmake.html Reporting Bugs ============== If you have found a bug: 1. If you have a patch, please read the `CONTRIBUTING.rst`_ document. 2. Otherwise, please join the `CMake Users List`_ 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