Coding Guideline

Contents

C++ Coding Guideline

  • Follow Google style for C++, with two exceptions:

    • Each line of text may contain up to 100 characters.

    • The use of C++ exceptions is allowed.

  • Use C++11 features such as smart pointers, braced initializers, lambda functions, and std::thread.

  • Use Doxygen to document all the interface code.

  • We have a series of automatic checks to ensure that all of our codebase complies with the Google style. Before submitting your pull request, you are encouraged to run the style checks on your machine. See R Coding Guideline.

Python Coding Guideline

R Coding Guideline

Code Style

  • We follow Google’s C++ Style guide for C++ code.

    • This is mainly to be consistent with the rest of the project.

    • Another reason is we will be able to check style automatically with a linter.

  • You can check the style of the code by typing the following command at root folder.

    make rcpplint
    
  • When needed, you can disable the linter warning of certain line with // NOLINT(*) comments.

  • We use roxygen for documenting the R package.

Rmarkdown Vignettes

Rmarkdown vignettes are placed in R-package/vignettes. These Rmarkdown files are not compiled. We host the compiled version on doc/R-package.

The following steps are followed to add a new Rmarkdown vignettes:

  • Add the original rmarkdown to R-package/vignettes.

  • Modify doc/R-package/Makefile to add the markdown files to be build.

  • Clone the dmlc/web-data repo to folder doc.

  • Now type the following command on doc/R-package:

    make the-markdown-to-make.md
    
  • This will generate the markdown, as well as the figures in doc/web-data/xgboost/knitr.

  • Modify the doc/R-package/index.md to point to the generated markdown.

  • Add the generated figure to the dmlc/web-data repo.

    • If you already cloned the repo to doc, this means git add

  • Create PR for both the markdown and dmlc/web-data.

  • You can also build the document locally by typing the following command at the doc directory:

    make html
    

The reason we do this is to avoid exploded repo size due to generated images.

R package versioning

See XGBoost Release Policy.

Registering native routines in R

According to R extension manual, it is good practice to register native routines and to disable symbol search. When any changes or additions are made to the C++ interface of the R package, please make corresponding changes in src/init.c as well.

Running Formatting Checks Locally

Once you submit a pull request to dmlc/xgboost, we perform two automatic checks to enforce coding style conventions. To expedite the code review process, you are encouraged to run the checks locally on your machine prior to submitting your pull request.

Linter

We use pylint and cpplint to enforce style convention and find potential errors. Linting is especially useful for Python, as we can catch many errors that would have otherwise occured at run-time.

To run this check locally, run the following command from the top level source tree:

cd /path/to/xgboost/
make lint

This command requires the Python packages pylint and cpplint.

Clang-tidy

Clang-tidy is an advance linter for C++ code, made by the LLVM team. We use it to conform our C++ codebase to modern C++ practices and conventions.

To run this check locally, run the following command from the top level source tree:

cd /path/to/xgboost/
python3 tests/ci_build/tidy.py --gtest-path=/path/to/google-test

where --gtest-path option specifies the full path of Google Test library.

Also, the script accepts two optional integer arguments, namely --cpp and --cuda. By default they are both set to 1, meaning that both C++ and CUDA code will be checked. If the CUDA toolkit is not installed on your machine, you’ll encounter an error. To exclude CUDA source from linting, use:

cd /path/to/xgboost/
python3 tests/ci_build/tidy.py --cuda=0 --gtest-path=/path/to/google-test

Similarly, if you want to exclude C++ source from linting:

cd /path/to/xgboost/
python3 tests/ci_build/tidy.py --cpp=0 --gtest-path=/path/to/google-test