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Adding FeatureSummary

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Henry Fredrick Schreiner 2018-04-06 11:29:56 +02:00
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chapters/features/modules.md
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@ -1,8 +1,8 @@
# Useful Modules
There are a ton of [modules] in CMake; but some of them are more useful than others. Here are a few highlights.
There are a ton of useful modules in CMake's «cmake:module» collection; but some of them are more useful than others. Here are a few highlights.
## [CMakeDependentOption]
## «module:CMakeDependentOption»
This adds a command `cmake_dependent_option` that sets an option based on another set of variables being true. It looks like this:
@ -26,14 +26,14 @@ if(NOT BUILD_TESTS_DEFAULT)
mark_as_advanced(BUILD_TESTS)
endif()
```
## [CMakePrintHelpers]
## «module:CMakePrintHelpers»
This module has a couple of handy output functions. `cmake_print_properties` lets you easily print properties.
And `cmake_print_variables` will print the names and values of any variables you give it.
## [CheckCXXCompilerFlag]
## «module:CheckCXXCompilerFlag»
This checks to see if a flag is supported. For example:
@ -47,7 +47,7 @@ Note that `OUTPUT_VARIABLE` will also appear in the configuration printout, so c
This is just one of many similar modules, such as `CheckIncludeFileCXX`, `CheckStructHasMember`, `TestBigEndian`, and `CheckTypeSize` that allow you
to check for information about the system (and you can communicate that to your source code).
## [WriteCompilerDetectionHeader]
## «module:WriteCompilerDetectionHeader»
This is an amazing module similar to the ones listed above, but special enough to deserve its own section. It allows you
to look for a list of features that some compilers support, and write out a C++ header file that lets you know whether that
@ -71,7 +71,7 @@ files using `OUTPUT_FILES_DIR
The downside is that you do have to list the compilers you expect to support. If you use the `ALLOW_UNKNOWN_COMPILERS` flag(s),
you can keep this from erroring on unknown compilers, but it will still leave all features empty.
## [try_compile](https://cmake.org/cmake/help/latest/command/try_compile.html)/[try_run](https://cmake.org/cmake/help/latest/command/try_run.html)
## «command:`try_compile`»/«command:`try_run`»
This is not exactly a module, but is crutial to many of the modules listed above. You can attept to compile (and possibly run) a bit of code at configure time. This can allow you to get information about the capabilities of your system. The basic syntax is:
@ -86,10 +86,37 @@ try_compile(
There are lots of options you can add, like `COMPILE_DEFINITIONS`. In CMake 3.8+, this will honor the CMake C/C++/CUDA standard settings. If you use `try_run` instead, it will run the resulting program and give you the output in `RUN_OUTPUT_VARIABLE`.
## «module:FeatureSummary»
This is a fairly useful but rather odd module. It allows you to print out a list of packages what were searched for, as well as any options you explicity mark. It's partially but not completely tied into «command:`find_package`». You first include the module, as always:
[modules]: https://cmake.org/cmake/help/latest/manual/cmake-modules.7.html
[CMakeDependentOption]: https://cmake.org/cmake/help/latest/module/CMakeDependentOption.html
[CheckCXXCompilerFlag]: https://cmake.org/cmake/help/latest/module/CheckCXXCompilerFlag.html
[WriteCompilerDetectionHeader]: https://cmake.org/cmake/help/latest/module/WriteCompilerDetectionHeader.html
[CMakePrintHelpers]: https://cmake.org/cmake/help/latest/module/CMakePrintHelpers.html
```cmake
include(FeatureSummary)
```
Then, for any find packages you have run or will run, you can extend the default information:
```cmake
set_package_properties(OpenMP PROPERTIES
URL "http://www.openmp.org"
DESCRIPTION "Parallel compiler directives"
PURPOSE "This is what it does in my package")
```
You can also set the `TYPE` of a package to `RUNTIME`, `OPTIONAL`, `RECOMMENDED`, or `REQUIRED`; you can't, however, lower the type of a package; if you have already added a `REQUIRED` package through «command:`find_package`» based on an option, you'll see it listed as `REQUIRED`.
And, you can mark any options as part of the feature summary:
```cmake
```
Then, you can print out the summary of features, either to the screen or a log file:
```cmake
if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
feature_summary(WHAT ENABLED_FEATURES DISABLED_FEATURES PACKAGES_FOUND)
feature_summary(FILENAME ${CMAKE_CURRENT_BINARY_DIR}/features.log WHAT ALL)
endif()
```
You can build any collection of `WHAT` items that you like, or just use `ALL`.