CONTRIBUTING.md

Development Model

Development generally follows the following ideas:

• New features are merged into to the development branch using Pull Requests (PRs).

  Nightly regression testing is used to ensure that no answers change (or if they do, that the changes were expected).

• Bug fixes, questions and contributions of new features are welcome!

  • Bugs should be reported through GitHub Issues.

  • We suggest asking questions through GitHub Discussions.

  • All contributions should be done via pull requests. A pull request should be generated from your fork of amrex and target the development branch. See below for details on how this process works.

    In general we squash commits upon merge to have a clean history. Please ensure that your PR title and first post are descriptive, since these will be used for a squashed commit message.

    Please note the following: If you choose to make contributions to the code then you hereby grant a non-exclusive, royalty-free perpetual license to install, use, modify, prepare derivative works, incorporate into other computer software, distribute, and sublicense such enhancements or derivative works thereof, in binary and source code form.

• On the first workday of each month, we make a tagged release. The merge window into development is closed a few days before the release day. While the merge window is closed, only bug fixes should be merged into development. Once the release is done, the merge window reopens.

Git workflow

AMReX uses git for version control. If you are new to git, you can follow one of these tutorials:

• Learn git with bitbucket
• git - the simple guide

Make your own fork and create a branch on it

The basic workflow is:

• Fork the main repo (or update it if you already created it).
• Implement your changes and push them on a new branch <branch_name> on your fork.
• Create a Pull Request from branch <branch_name> on your fork to branch development on the main AMReX repository.

First, let us setup your local git repo. To make your own fork of the main (upstream) repository, press the fork button on the AMReX Github page.

Note: If you already had a fork of AMReX prior to 4/17/2020, we recommend deleting it and re-forking. This is due to a history re-write on the main repository. Note that you will lose any branches on your fork that haven't been merged into main development yet.

Then, clone your fork on your local computer. If you plan on doing a lot of amrex development, we recommend configuring your clone to use ssh access so you won't have to enter your Github password every time, which you can do using these commands:

git clone --branch development [email protected]:<myGithubUsername>/amrex.git

# Then, navigate into your repo, add a new remote for the main AMReX repo, and fetch it:
cd amrex
git remote add upstream https://github.com/AMReX-Codes/amrex
git remote set-url --push upstream [email protected]:<myGithubUsername>/amrex.git
git fetch upstream

# We recommend setting your development branch to track the upstream one instead of your fork:
git branch -u upstream/development

For instructions on setting up SSH access to your Github account on a new machine, see here.

If you instead prefer to use HTTPS authentication, configure your local clone as follows:

git clone --branch development https://github.com/<myGithubUsername>/amrex.git

# Navigate into your repo, add a new remote for the main AMReX repo, and fetch it
cd amrex
git remote add upstream https://github.com/AMReX-Codes/amrex
git remote set-url --push upstream https://github.com/<myGithubUsername>/amrex.git
git fetch upstream

# We recommend setting your development branch to track the upstream one instead of your fork:
git branch -u upstream/development

Now you are free to play with your fork (for additional information, you can visit the Github fork help page).

Note: you do not have to re-do the setup above every time. Instead, in the future, you need to update the development branch on your fork with

git checkout development
git pull

Make sure you are on the development branch with

git checkout development

in the AMReX directory.

Create a branch <branch_name> (the branch name should reflect the piece of code you want to add, like high_order_interpolation) with

git checkout -b <branch_name>

and do the coding you want. Add the files you work on to the git staging area with

git add <file_I_created> <and_file_I_modified>

Commit & push your changes

Periodically commit your changes with

git commit -m "This is a 50-char description to explain my work"

The commit message (between quotation marks) is super important in order to follow the developments and identify bugs.

For the moment, commits are on your local repo only. You can push them to your fork with

git push -u origin <branch_name>

If you want to synchronize your branch with the development branch (this is useful when development is being modified while you are working on <branch_name>), you can use

git pull upstream development

and fix any conflicts that may occur.

Do not merge your branch for PR into your local development branch, because it will make your local development branch diverge from the matching branch in the main repository after your PR is merged.

Submit a Pull Request

A Pull Request is the way to efficiently visualize the changes you made and to propose your new feature/improvement/fix to the AMReX project. Right after you push changes, a banner should appear on the Github page of your fork, with your <branch_name>.

• Click on the compare & pull request button to prepare your PR.
• It is time to communicate your changes: write a title and a description for your PR. People who review your PR are happy to know
  • what feature/fix you propose, and why
  • how you made it (created a new class than inherits from...)
  • and anything relevant to your PR (performance tests, images, etc.)
• Press Create pull request. Now you can navigate through your PR, which highlights the changes you made.

Please DO NOT write large Pull Requests, as they are very difficult and time-consuming to review. As much as possible, split them into small, targeted PRs. For example, if find typos in the documentation open a pull request that only fixes typos. If you want to fix a bug, make a small pull request that only fixes a bug. If you want to implement a large feature, write helper functionality first, test it and submit those as a first pull request. If you want to implement a feature and are not too sure how to split it, just open a discussion about your plans and ping other AMReX developers on it to chime in.

Even before your work is ready to merge, it can be convenient to create a PR (so you can use Github tools to visualize your changes). In this case, please make a "draft" PR using the drop-down menu next to the "Create pull request" button.

Once your pull request is made, we will review and potentially merge it. We recommend always creating a new branch for each pull request, as per the above instructions. Once your pull request is merged, you can delete your local PR branch with

git branch -D <branch_name>

and you can delete the remote one on your fork with

git push origin --delete <branch_name>

Generally speaking, you want to follow the following rules.

• Do not merge your branch for PR into your local development branch that tracks AMReX development branch. Otherwise your local development branch will diverge from AMReX development branch.

• Do not commit in your development branch that tracks AMReX development branch.

• Always create a new branch based off development branch for each pull request, unless you are going to use git to fix it later.

If you have accidentally committed in development branch, you can fix it as follows,

git checkout -b new_branch
git checkout development
git reset HEAD~2  # Here 2 is the number of commits you have accidentally committed in development
git checkout .

After this, the local development should be in sync with AMReX development and your recent commits have been saved in new_branch branch.

If for some reason your PR branch has diverged from AMReX, you can try to fix it as follows. Before you try it, you should back up your code in case things might go wrong.

git fetch upstream   # assuming upstream is the remote name for the official amrex repo
git checkout -b xxx upstream/development  # replace xxx with whatever name you like
git branch -D development
git checkout -b development upstream/development
git checkout xxx
git merge yyy  # here yyy is your PR branch with unclean history
git rebase -i upstream/development

You will see something like below in your editor,

pick 7451d9d commit message a
pick c4c2459 commit message b
pick 6fj3g90 commit message c

This now requires a bit of knowledge on what those commits are, which commits have been merged, which commits are actually new. However, you should only see your only commits. So it should be easy to figure out which commits have already been merged. Assuming the first two commits have been merged, you can drop them by replace pick with drop,

drop 7451d9d commit message a
drop c4c2459 commit message b
pick 6fj3g90 commit message c

After saving and then exiting the editor, git log should show a clean history based on top of development branch. You can also do git diff yyy..xxx to make sure nothing new was dropped. If all goes well, you can submit a PR using xxx branch. Don't worry, if something goes wrong during the rebase, you an always git rebase --abort and start over.

AMReX Coding Style Guide

Code Guidelines

AMReX developers should adhere to the following coding guidelines:

• Indentations should use 4 spaces, not tabs.
• Use curly braces for single statement blocks. For example:

       for (int n=0; n<10; ++n) {
           Print() << "Like this!";
       }

or

       for (int n=0; n<10; ++n) { Print() << "Like this!"; }

but not

       for (int n=0; n<10; ++n) Print() << "Not like this.";

or

       for (int n=0; n<10; ++n)
          Print() << "Not like this.";

• Add a space after the function name and before the parenthesis of the parameter list (but not when simply calling the function). For example:

        void CorrectFunctionDec (int input)

Not

        void IncorrectFunctionDec(int input)

This makes it easy to find where functions are defined with grep.

• Member variables should be prefixed with m_. For example:

       amrex::Real m_variable;

These guidelines should be adhered to in new contributions to AMReX, but please refrain from making stylistic changes to unrelated sections of code in your PRs.

API Documentation Using Doxygen

The Doxygen documentation is designed for advanced user-developers. It aims to maximize the efficiency of a search-and-find style of locating information. Doxygen style comment blocks should proceed the namespace, class, function, etc. to be documented where appropriate. For example:

   /**
    * \brief A one line description.
    *
    * \param[in] variable A short description of the variable.
    * \param[inout] data The value of data is read and changed.
    *
    * A longer description can be included here.
    */

    void MyFunction (int variable, MultiFab& data){
    ...

Additional information regarding Doxygen comment formatting can be found in the Doxygen Manual.

Core Developers

People who make a number of substantive contributions will be named "core developers" of AMReX. The criteria for becoming a core developer are flexible, but generally involve one of the following:

• 100 non-trivial commits to amrex/Src/ and/or

• addition of a new algorithm / module and/or

• substantial input into the code design process or testing

If a core developer is inactive for multiple years, we may reassess their status as a core developer.

The current list of core developers is: Ann Almgren (LBNL), Vince Beckner, John Bell (LBNL), Johannes Blaschke (LBNL), Cy Chan (LBNL), Marcus Day (LBNL), Brian Friesen (NERSC), Kevin Gott (NERSC), Daniel Graves (LBNL), Axel Huebl (LBNL), Max Katz (NVIDIA), Andrew Myers (LBNL), Tan Nguyen (LBNL), Andrew Nonaka (LBNL), Michele Rosso (LBNL), Sam Williams (LBNL), Weiqun Zhang (LBNL), Michael Zingale (Stony Brook University).