vtk-m2/CONTRIBUTING.md

Contributing to VTK-m

This page documents how to develop VTK-m through Git.

Git is an extremely powerful version control tool that supports many different "workflows" for individual development and collaboration. Here we document procedures used by the VTK-m development community. In the interest of simplicity and brevity we do not provide an explanation of why we use this approach.

Setup

Before you begin, perform initial setup:

1. Register GitLab Access to create an account and select a user name.

2. Fork VTK-m into your user's namespace on GitLab.

3. Follow the download instructions to create a local clone of the main VTK repository:

   $ git clone https://gitlab.kitware.com/vtk/vtk-m.git VTK
   $ cd vtk-m
   

   The main repository will be configured as your origin remote.

4. (Optional but highly recommended.) Register with the VTK-m project on Kitware's CDash instance to better know how your code performs in regression tests. After registering and signing in, click on "All Dashboards" link in the upper left corner, scroll down and click "Subscribe to this project" on the right of VTK-m.

Workflow

VTK-m development uses a branchy workflow based on topic branches. Our collaboration workflow consists of three main steps:

1. Local Development:

   • Update
   • Create a Topic

2. Code Review (requires GitLab Access):

   • Share a Topic
   • Create a Merge Request
   • Review a Merge Request
   • Revise a Topic

3. Integrate Changes:

   • Merge a Topic (requires permission in GitLab)

Update

1. Update your local master branch:

   $ git checkout master
   $ git pull
   

2. Optionally push master to your fork in GitLab:

   $ git push gitlab master
   

Create a Topic

All new work must be committed on topic branches. Name topics like you might name functions: concise but precise. A reader should have a general idea of the feature or fix to be developed given just the branch name.

1. To start a new topic branch:

   $ git fetch origin
   

2. For new development, start the topic from origin/master:

   $ git checkout -b my-topic origin/master
   

3. Edit files and create commits (repeat as needed):

   $ edit file1 file2 file3
   $ git add file1 file2 file3
   $ git commit
   

   Caveats:

   • Data files must be placed in either the root data directory, or a folder explicitly named 'data'. This is required as VTK-m uses Git-LFS to efficiently support data files.

Guidelines for Commit Messages

Remember to motivate & summarize. When writing commit messages, get into the habit of creating messages that have enough information for any developer to read and glean relevant information such as:

1. Is this change important and why?
2. If addressing an issue, which issue(s)?
3. If a new feature, why is it useful and/or necessary?
4. Are there background references or documentation?

A short description of what the issue being addressed and how will go a long way towards making the log more readable and the software more maintainable. VTK-m requires that your message start with a single subject line, followed by a blank line, followed by the message body which contains the more detailed explanatory text for the commit. You can consider a commit message to very similar to an email with the first line being the subject of an email and the rest of the text as the body.

Style guidelines for commit messages are as follows:

1. Separate subject from body with a blank line
2. Limit the subject line to 78 characters
3. Capitalize the subject line
4. Use the imperative mood in the subject line e.g. "Refactor foo" or "Fix Issue #12322", instead of "Refactoring foo", or "Fixing issue #12322".
5. Wrap the body at 80 characters
6. Use the body to explain what and why and if applicable a brief how.

Share a Topic

When a topic is ready for review and possible inclusion, share it by pushing to a fork of your repository in GitLab. Be sure you have registered and signed in for GitLab Access and created your fork by visiting the main VTK-m GitLab repository page and using the "Fork" button in the upper right.

1. Checkout the topic if it is not your current branch:

   $ git checkout my-topic
   

2. Push commits in your topic branch to your fork in GitLab:

   $ git push gitlab HEAD
   

   Notes:

   • If you are revising a previously pushed topic and have rewritten the topic history, add -f or --force to overwrite the destination.

   The output will include a link to the topic branch in your fork in GitLab and a link to a page for creating a Merge Request.

Create a Merge Request

Visit your fork in GitLab, browse to the "Merge Requests" link on the left, and use the "New Merge Request" button in the upper right to reach the URL printed at the end of the previous step. It should be of the form:

https://gitlab.kitware.com/<username>/vtk-m/merge_requests/new

Follow these steps:

1. In the "Source branch" box select the <username>/vtk-m repository and the my-topic branch.

2. In the "Target branch" box select the vtk/vtk-m repository and the master branch. It should be the default.

3. Use the "Compare branches" button to proceed to the next page and fill out the merge request creation form.

4. In the "Title" field provide a one-line summary of the entire topic. This will become the title of the Merge Request.

   Example Merge Request Title:

   Add OpenMP Device Adapter
   

5. In the "Description" field provide a high-level description of the change the topic makes and any relevant information about how to try it.

   • Use @username syntax to draw attention of specific developers. This syntax may be used anywhere outside literal text and code blocks. Or, wait until the next step and add comments to draw attention of developers.
   • Optionally use a fenced code block with type message to specify text to be included in the generated merge commit message when the topic is merged.

   Example Merge Request Description:

   This branch adds a new device adapter that uses new OpenMP 4+ features
   including Task groups to better handle unbalanced and irregular domains
   
   ```message
   Add a OpenMP 4+ task-based device adapter.
   ```
   
   Cc: @user1 @user2
   

6. The "Assign to", "Milestone", and "Labels" fields may be left blank.

7. Use the "Submit merge request" button to create the merge request and visit its page.

Guidelines for Merge Requests

Remember to motivate & summarize. When creating a merge request, consider the reviewers and future perusers of the software. Provide enough information to motivate the merge request such as:

1. Is this merge request important and why?
2. If addressing an issue, which issue(s)?
3. If a new feature, why is it useful and/or necessary?
4. Are there background references or documentation?

Also provide a summary statement expressing what you did and if there is a choice in implementation or design pattern, the rationale for choosing a certain path. Notable software or data features should be mentioned as well.

A well written merge request will motivate your reviewers, and bring them up to speed faster. Future software developers will be able to understand the reasons why something was done, and possibly avoid chasing down dead ends, Although it may take you a little more time to write a good merge request, you’ll likely see payback in faster reviews and better understood and maintainable software.

Review a Merge Request

Add comments mentioning specific developers using @username syntax to draw their attention and have the topic reviewed. After typing @ and some text, GitLab will offer completions for developers whose real names or user names match.

Comments use GitLab Flavored Markdown for formatting. See GitLab documentation on Special GitLab References to add links to things like merge requests and commits in other repositories.

Reviews

Reviewers may add comments providing feedback or to acknowledge their approval. All comments use the GitLab Flavored Markdown, any line of a comment may be exactly one of the following votes followed by nothing but whitespace before the end of the line:

• -1 or 👎 (:-1:) means "The change is not ready for integration."
• +1 or 👍 (:+1:) means "The change is ready for integration."

These are used to inform the author that a merge srequest has been approved for [merging]((#merge-a-topic).

Fetching Changes ####s

One may fetch the changes associated with a merge request by using the git fetch command line shown at the top of the Merge Request page. It is of the form:

$ git fetch https://gitlab.kitware.com/$username/vtk-m.git $branch

This updates the local FETCH_HEAD to refer to the branch.

There are a few options for checking out the changes in a work tree:

• One may checkout the branch:

  $ git checkout FETCH_HEAD -b $branch
  

  or checkout the commit without creating a local branch:

  $ git checkout FETCH_HEAD
  

• Or, one may cherry-pick the commits to minimize rebuild time:

  $ git cherry-pick ..FETCH_HEAD
  

Robot Reviews

The "Kitware Robot" automatically performs basic checks on the commits and adds a comment acknowledging or rejecting the topic. This will be repeated automatically whenever the topic is updated. A re-check may be explicitly requested by adding a comment with a single trailing line:

Do: check

A topic cannot be merged until the automatic review succeeds.

Testing

VTK-m has a buildbot instance watching for merge requests to test. Each time a merge request is updated the buildbot user (@buildbot) will automatically trigger a new build on all VTK-m buildbot workers. The buildbot user (@buildbot) will respond with a comment linking to the CDash results when it schedules builds.

The buildbot user (@buildbot) will also respond to any comment with the form:

Do: test

The Do: test command accepts the following arguments:

• --oneshot only build the current hash of the branch; updates will not be built using this command
• --stop clear the list of commands for the merge request
• --superbuild build the superbuilds related to the project
• --clear clear previous commands before adding this command
• --regex-include <arg> or -i <arg> only build on builders matching <arg> (a Python regular expression)
• --regex-exclude <arg> or -e <arg> excludes builds on builders matching <arg> (a Python regular expression)

Multiple Do: test commands may be given in separate comments. Buildbot may skip tests for older branch updates that have not started before a test for a new update is requested.

Builder names always follow this pattern:

    project-host-os-libtype-buildtype+feature1+feature2

• project: always vtk-m
• host: the buildbot host
• os: one of windows, osx, or linux
• libtype: shared or static
• buildtype: release or debug
• feature: alphabetical list of features enabled for the build

Revise a Topic

If a topic is approved during GitLab review, skip to the next step. Otherwise, revise the topic and push it back to GitLab for another review as follows:

1. Checkout the topic if it is not your current branch:

   $ git checkout my-topic
   

2. To revise the 3rd commit back on the topic:

   $ git rebase -i HEAD~3
   

   (Substitute the correct number of commits back, as low as 1.) Follow Git's interactive instructions.

3. Return to the above step to share the revised topic.

Merge a Topic

After a topic has been reviewed and approved in a GitLab Merge Request, authorized developers may add a comment with a single trailing line:

Do: merge

to ask that the change be merged into the upstream repository. By convention, only merge if you have recieved +1 . Do not request a merge if any -1 review comments have not been resolved.

Merge Success

If the merge succeeds the topic will appear in the upstream repository master branch and the Merge Request will be closed automatically.

Merge Failure

If the merge fails (likely due to a conflict), a comment will be added describing the failure. In the case of a conflict, fetch the latest upstream history and rebase on it:

$ git fetch origin
$ git rebase origin/master

Return to the above step to share the revised topic.