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README.adoc

clang-format

Introduction

This example shows how to call the Clang Format to check if your source code matches against your code style guidelines.

The files included in this example are:

$ tree
.
├── .clang-format
├── CMakeLists.txt
├── cmake
│   ├── modules
│   │   ├── clang-format.cmake
│   │   └── FindClangFormat.cmake
│   └── scripts
│       └── clang-format-check-changed
├── subproject1
│   ├── CMakeLists.txt
│   └── main1.cpp
└── subproject2
    ├── CMakeLists.txt
    └── main2.cpp

Requirements

To run this example you must have clang format tool installed. This can be installed on Ubuntu using the following command.

$ sudo apt-get install clang-format-3.6

It will result in the tool being available as:

$ clang-format-3.6

If you install a different version, you can edit the CLANG_FORMAT_BIN_NAME variable in the root CMakeLists.txt

Concepts

clang-format

clang-format can scan a source file then find and optionally format it to match your companys style guidelines. There are default styles build in but you can also setup a style guide using a custom file called .clang-format, for example a snipped from this repositories .clang-format is below:

Language:        Cpp
# BasedOnStyle:  LLVM
AccessModifierOffset: -4
AlignAfterOpenBracket: Align
AlignConsecutiveAssignments: false
AlignConsecutiveDeclarations: false

format style

As mentioned, the style in this example is based on the .clang-format file. This can be changed by editing clang-format.cmake and changing the -style=file to the required style;

Targets

This example will setup 3 targets:

  • format

  • format-check

  • format-check-changed

format

The format target will find any C++ source files and in place modify them to match the .clang-format style. The source files are found using the following cmake code

file(GLOB_RECURSE ALL_SOURCE_FILES *.cpp *.h *.cxx *.hxx *.hpp *.cc *.ipp)

# Don't include some common build folders
set(CLANG_FORMAT_EXCLUDE_PATTERNS ${CLANG_FORMAT_EXCLUDE_PATTERNS} "/CMakeFiles/" "cmake")

# get all project files file
foreach (SOURCE_FILE ${ALL_SOURCE_FILES})
    foreach (EXCLUDE_PATTERN ${CLANG_FORMAT_EXCLUDE_PATTERNS})
        string(FIND ${SOURCE_FILE} ${EXCLUDE_PATTERN} EXCLUDE_FOUND)
        if (NOT ${EXCLUDE_FOUND} EQUAL -1)
            list(REMOVE_ITEM ALL_SOURCE_FILES ${SOURCE_FILE})
        endif ()
    endforeach ()
endforeach ()

This will find files matching the common C++ suffixes and then remove any that match some common CMake directories.

In the root CMakeList.txt we also exclude the build directory by adding the line

set(CLANG_FORMAT_EXCLUDE_PATTERNS  "build/")

format-check

This target will work as above but instead of formatting the files it will cause a failure if any files don’t match the clang-format style

format-check-changed

This target will check the output of git status and scan the files to check if they match the style. This can be used by developers to make sure their changed files match the correct style.

In this example the actual check is done with a helper script clang-format-check-changed.py. This script will run git status --porcelain --ignore-submodules to get a list of changed files, match them against the allowed extensions from the above list, and finally remove any that match the exclude pattern from CLANG_FORMAT_EXCLUDE_PATTERNS. It will then run these files through clang-format and exit with an error if the files do not match the style.

An example call to the clang-format-check-changed.py script is:

cmake/scripts/clang-format-check-changed.py --file-extensions ".cpp,*.cpp,*.h,*.cxx,*.hxx,*.hpp,*.cc,*.ipp" --exclude=build/ --exclude=/CMakeFiles/ --exclude=cmake --clang-format-bin /usr/bin/clang-format-3.6
Note

This will include all changed files in your git repository that match the patterns. In this example repository this can include files that are part of different examples.