This document describes both C development guidelines adopted by HPC team, and the tools and processes required to ensure they are properly followed over time.

Development Guidelines are split in the following sections:

• Tooling
• Development Lifecycle
• Code Formatting
• Naming Conventions
• Code Documentation
• Best Practices
• Python bindings

This project in currently under development, and shall not provide the features its documentation pretends. Here is a raw summary of the status:

This directory provides a CMake project that allows one to use the tools and the processes described in this document. This project requires CMake version 3.10 or higher.

This CMake project expects for the following utilities to be available:

• Python 3.5 or higher
• ClangFormat 9
• ClangTidy 7
• cmake-format Python package version 0.6
• pre-commit Python package
• git version control system 2.17 or higher.

Optionally, it will also look for:

• valgrind memory checker
• code coverage utilities like gcov, lcov, or gcov

You can import this CMake project into your Git repository using a git submodule:

git submodule add https://github.com/BlueBrain/hpc-coding-conventions.git
git submodule update --init --recursive

Note: if your project already has a cmake sub-directory, it is recommended to create the submodule in this directory instead of top-level.

Then simply add the following line in the top CMakeLists.txt, after your project declaration:

project(mylib CXX)
# [...]
add_subdirectory(hpc-coding-conventions/cpp)

After cloning or updating this git submodule, run CMake to take benefits of the latest changes. This will setup or update git pre-commit hooks of this repository.

CMake variables defined by this project are prefixed by ${PROJECT_NAME} by default. The CMake variable CODING_CONV_PREFIX allows to specify another prefix. It must be defined before including this CMake project, for instance:

project(mylib CXX)
# [...]
set(CODING_CONV_PREFIX Foo)
add_subdirectory(hpc-coding-conventions/cpp)

Create file .bbp-project.yaml at the root of your project and enable the formatting tools, you want to enable, for instance:

tools:
  ClangFormat:
    enable: True
  CMakeFormat:
    enable: True

You can then use the bin/format utility.

bin/format relies on PATH environment variable to locate the proper tools. You can override the default required versions specified in bbp-project.yaml:

tools:
  ClangFormat:
    enable: True
    version: ~=15.0.0

It is also possible to override the path to a tool in the YAML config file:

tools:
  CMakeFormat:
    path: /path/to/bin/cmake-format

• To format the entire codebase: /path/to/hpc-coding-conventions/bin/format
• To check the formatting: /path/to/hpc-coding-conventions/bin/format -n
• To format the CMake files only: /path/to/hpc-coding-conventions/bin/format --lang CMake
• To check the formatting of C files in a specific locations: /path/to/hpc-coding-conventions/bin/format -n --lang c src/path1/ /src/path2/foo.cpp

You can override the default file filters of a tool, for instance:

tools:
  ClangFormat:
    include:
      match: &cpp_patterns
      - src/steps/.*\.((h)|(cpp)|(hpp))
      - test/unit/.*\.((h)|(cpp)|(hpp))
    path: /foo/bin/clang-format
  ClangTidy:
    include:
      match: *cpp_patterns

These coding conventions come with a predefined configuration of ClangFormat that is by default copied in the top directory of the project.

It is recommended to not add this .clang-format to git so that it is fully driven by this project. It will get updated along with the evolution of these guidelines. Thus it is recommended to inform git to ignore this file by adding it to the top .gitignore.

A project can however override the predefined configuration of ClangFormat in two ways:

1. Create a .clang-format.changes containing only the required modifications.
2. Add .clang-format to the git repository. This project will never try to modify it.

Like ClangFormat, these coding conventions already provide a CMakeFormat configuration that the user can customize with a file named .cmake-format.changes.yaml placed at the project's root directory. This file can be used to specify the signature of owned CMake functions and macros, for instance:

additional_commands:
  add_mpi_test:
    kwargs:
      NAME: 1
      NUM_PROCS: 1
      COMMAND: '*'

will allow CMakeFormat to properly format functions calls like below:

add_mpi_test(
  NAME OpSplitOmega_h_2D
  NUM_PROCS 2
  COMMAND $<TARGET_FILE:OpSplitOmega_h> --num-iterations 100 square.msh)

Define ${PROJECT}_TEST_FORMATTING:BOOL CMake variable to enforce formatting during the test make target.

To activate static analysis of C files with clang-tidy within CMake, enable the CMake variable ${PROJECT}_STATIC_ANALYSIS where ${PROJECT} is the name given to the CMake project function. For instance, given a project foo: cmake -DFoo_STATIC_ANALYSIS:BOOL=ON <path> Whenever a C file is compiled by CMake, clang-tidy will be called.

You can also use utility: bin/clang-tidy

This will provide a clang-tidy make target that will perform static analysis of all C files. Target fails as soon as one defect is detected among the files.

It will also activate static analysis report during the compilation phase.

The following CMake cache variables can be used to customize the static analysis of the code:

• ${PROJECT}_ClangTidy_DEPENDENCIES: list of CMake targets to build before check C/C code. Default value is ""

These variables are meant to be overridden inside your CMake project. They are CMake CACHE variables whose value must be forced before including this CMake project.

These coding conventions come with a .clang-tidy file providing a predefined list of ClangTidy checks. By default, this file is copied in the top directory of the project.

It is recommended to not add this .clang-tidy to git so that it is fully driven by this project. It will get updated along with the evolution of these guidelines. Thus it is recommended to inform git to ignore this file by adding it to the top .gitignore.

A project can however override the predefined configuration of ClangFormat in two ways:

1. Create a .clang-tidy.changes containing only the required modifications.
2. Add .clang-tidy to the git repository. This project will never try to modify it.

Enable CMake option ${PROJECT}_GIT_HOOKS to enable automatic checks before committing or pushing with git. the git operation will fail if one of the registered checks fails.

The following checks are available:

• check-clang-format: check C formatting
• check-cmake-format: check CMake formatting
• clang-tidy: execute static-analysis
• courtesy-msg: print a courtesy message to the console. This check never fails. The default message is a reminder to test and format the changes when pushing a contribution with git. A project can overwrite the message displayed by adding the CMake template named .git-push-message.cmake.in at the root of the project directory.

To enable these checks, use CMake variables ${PROJECT}_GIT_COMMIT_HOOKS and ${PROJECT}_GIT_PUSH_HOOKS to specify which checks should be executed for each specific git operation. For instance:

cmake -Dfoo_GIT_COMMIT_HOOKS=clang-tidy \ -Dfoo_GIT_PUSH_HOOKS=check-clang-format,courtesy-msg <path>

This feature requires the pre-commit utility.

bob.cmake is a CMake utility file part of hpc-coding-conventions that provides a set of convenient macros and functions used to:

• specify your project options and dependencies
• specify the proper compilation flags
• install the proper CMake export flags so that your project can be loaded by another project with the find_package CMake function.

By default, CMake relies on the CMAKE_BUILD_TYPE variable to set the proper compilation flags. Because bob is now taking care of it, you must configure your project with CMAKE_BUILD_TYPE empty.

bob sets the compilation flags according to a set of CMake variables:

• ${PROJECT_NAME}_CXX_OPTIMIZE:BOOL: Compile C with optimization (default is ON)
• ${PROJECT_NAME}_CXX_SYMBOLS:BOOL: Compile C with debug symbols (default is ON)
• ${PROJECT_NAME}_CXX_WARNINGS:BOOL: Compile C with warnings" (default is ON)
• ${PROJECT_NAME}_EXTRA_CXX_FLAGS:STRING: Additional C compilation flags
• ${PROJECT_NAME}_CXX_FLAGS:STRING: bypass variables above and use the specified compilation flags. CMAKE_BUILD_TYPE is ignored.
• ${PROJECT_NAME}_NORMAL_CXX_FLAGS:BOOL: Allow CMAKE_CXX_FLAGS to follow normal CMake behavior and bypass all variables above.

Default CMAKE_CXX_FLAGS variable value is taken into account.

The top-level CMakelists.txt of your project may look like:

cmake_minimum_required(VERSION 3.10)
project(HelloWorld VERSION 1.0.0 LANGUAGES CXX)
add_subdirectory(hpc-coding-conventions/cpp)

bob_begin_package()
bob_begin_cxx_flags()
bob_cxx17_flags()
# specify custom compilation flags
find_package(OpenMP)
if(OpenMP_FOUND)
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
  set(CMAKE_FLAGS "${CMAKE_FLAGS} ${OpenMP_FLAGS}")
else()
  message(WARNING "OpenMP support is disabled because it could not be found.")
endif()
bob_end_cxx_flags()

# specify your targets:
add_library(...)
add_executable(...)

bob_end_package()

External libraries required to build or test your C project can be either directly added to the git repository or as a git submodule. The standard root location for this kind of files is the 3rdparty/ directory but can be overriden with the ${PROJECT_NAME}_3RDPARTY_DIR CMake variable.

Adding single-file/header-only C libraries directly to the git repository of your project is acceptable in general, like catch2 or the JSON library of Niels Lohmann for instance.

More significant dependencies should be considered as pure external dependencies. But it can also be very convenient to have them as git submodules, and be able to switch between the two.

This project provides helper functions to deal with these dependencies:

#
# cpp_cc_git_submodule(source_dir
#                      [DISABLED]
#                      SUBDIR path
#                      [BUILD] [<arguments>]
#                      [PACKAGE] [<arguments>]
#                      GIT_ARGS [<arguments>])
#
# Add a CMake option in the cache to control whether the
# submodule is used or not (default ON). The option is named after the source
# directory passed in first argument, for instance:
#   cpp_cc_git_submodule(src/eigen)
# adds the following CMake cached option:
#  ${PROJECT_NAME}_3RDPARTY_USE_SRC_EIGEN:BOOL=ON
#
# If enabled, then the submodule is fetched if missing in the working copy.
#
# If the DISABLED argument is provided, then the default value for the CMake
# option is OFF.
#
# If the BUILD argument is provided then the directory is added to the build
# through the add_subdirectory CMake function. Arguments following the BUILD
# arguments are passed to the add_subdirectory function call.
#
# The optional SUBDIR argument is used by the BUILD argument to determine
# the path to the directory added to the build. The path specified is relative
# to the path to the git submodule.
#
# If the PACKAGE argument is provided and the CMake option to determine whether
# the git submodule should be used or not is FALSE, then a call to the find_package
# function is made with the arguments specified to the PACKAGE option.
#
# Default options passed to the `git submodule update` command are
# `--init --recursive --depth 1` to perform a shallow clone of the submodule.
# If the GIT_ARGS argument is provided, then its value supersedes the default options.
#

Should you want to contribute to the naming conventions, please refer to the dedicated contributing document first.

The development of this software was supported by funding to the Blue Brain Project, a research center of the École polytechnique fédérale de Lausanne (EPFL), from the Swiss government's ETH Board of the Swiss Federal Institutes of Technology.

Copyright © 2019-2022 Blue Brain Project/EPFL