e15a7075b5
A common idiom in CMake-based build systems is to have custom commands that generate files not listed explicitly as outputs so that these files do not have to be newer than the inputs. The file modification times of such "byproducts" are updated only when their content changes. Then other build rules can depend on the byproducts explicitly so that their dependents rebuild when the content of the original byproducts really does change. This "undeclared byproduct" approach is necessary for Makefile, VS, and Xcode build tools because if a byproduct were listed as an output of a rule then the rule would always rerun when the input is newer than the byproduct but the byproduct may never be updated. Ninja solves this problem by offering a 'restat' feature to check whether an output was really modified after running a rule and tracking the fact that it is up to date separately from its timestamp. However, Ninja also stats all dependencies up front and will only restat files that are listed as outputs of rules with the 'restat' option enabled. Therefore an undeclared byproduct that does not exist at the start of the build will be considered missing and the build will fail even if other dependencies would cause the byproduct to be available before its dependents build. CMake works around this limitation by adding 'phony' build rules for custom command dependencies in the build tree that do not have any explicit specification of what produces them. This is not optimal because it prevents Ninja from reporting an error when an input to a rule really is missing. A better approach is to allow projects to explicitly specify the byproducts of their custom commands so that no phony rules are needed for them. In order to work with the non-Ninja generators, the byproducts must be known separately from the outputs. Add a new "BYPRODUCTS" option to the add_custom_command and add_custom_target commands to specify byproducts explicitly. Teach the Ninja generator to specify byproducts as outputs of the custom commands. In the case of POST_BUILD, PRE_LINK, and PRE_BUILD events on targets that link, the byproducts must be specified as outputs of the link rule that runs the commands. Activate 'restat' for such rules so that Ninja knows it needs to check the byproducts, but not for link rules that have no byproducts.
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`: http://www.cmake.org .. _`CMake Documentation Page`: http://www.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`: http://www.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 the 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`: http://www.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`: http://www.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 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`: http://www.cmake.org/Bug Contributing ============ See `CONTRIBUTING.rst`_ for instructions to contribute. .. _`CONTRIBUTING.rst`: CONTRIBUTING.rst