Thank you for your interest in contributing to OpenTripPlanner. This document will give you some pointers on how to contact and coordinate with the OTP development team, as well as a description of the contribution process and expectations.
If you have any questions about problems you are encountering with code, deployment, documentation, or development coordination, please don't hesitate to post to the OpenTripPlanner discussion groups. These are Google Groups which can be accessed as web forums or as traditional email mailing lists:
- https://groups.google.com/g/opentripplanner-dev (opentripplanner-dev@googlegroups.com)
- https://groups.google.com/g/opentripplanner-users (opentripplanner-users@googlegroups.com)
Any message posted there will be seen by most of the contributors, some of whom work on OTP full time. It will also create a record of the discussion that will be useful to the larger community and often leads to issues being discussed at the twice-weekly development meetings.
OTP development meetings usually occur twice a week. These meetings are open to anyone who wants to join, even if you simply want to observe the process or ask a few questions. The most effective way to advance pull requests and collaborate is to participate directly in these meetings. The meeting times have been deliberately chosen to allow participation during regular business hours across as many time zones as possible, from the eastern Americas through Europe and Africa to Asia. If these times are not suitable for you, please let us know and we will attempt to schedule a call at a time that suits you.
Check the specific times on this calendar which will be updated to reflect holidays or changes to meeting times. Note that times on this calendar are expressed in the Central European time zone by default. There is also an iCal link to import this calendar into calendar apps. Check the details of the calendar events for the Google Meet link, which is different on different days of the week.
Our primary tools for organizing development are Github issues and pull requests. When creating issues and pull requests, please follow the instructions in the template: always specify the version of OTP you are running and provide command lines and configuration files, do not leave remnants of the instructions in your submitted text etc.
OpenTripPlanner has been in active development and use for well over a decade and is now relied upon as infrastructure by large organizations and millions of public transit passengers around the world. These organizations have invested a great deal of time, effort, and money in this project, and some have gone all-in supporting and relying on OTP over the long term. Accordingly, when working on OpenTripPlanner 2 we have decided to make code quality and maintainability a top priority, and have built up a culture of active collaboration and code review to support this. At this stage, the project has relatively high expectations on code quality and a desire to maintain a professional and orderly development process.
We welcome well-documented bug reports as Github Issues, and pull requests sharing your patches and new features. However, for all but the simplest bugfixes and documentation updates, please be aware that pull requests will be subject to review and you will almost certainly be asked to explain use cases, ensure encapsulation and integration with the rest of the system, and provide some assurance that there is an organizational commitment to long term maintenance.
Most of the contributors to OTP2 are full-time software developers working for organizations with a long term stake in OpenTripPlanner, and are professionally bound to ensure its reliability and efficiency. It is an accepted fact among this team that a large part, perhaps the most important part of software development is careful design and communication with current collaborators and future maintainers of the system.
You will see a steady stream of pull requests being merged from different organizations. What almost all these have in common is that their authors participated in the weekly meetings, at which they discussed the problem or feature they were addressing, answered questions from the other developers about their design and implementation, and were open to making changes based on the consensus reached at those meetings. If you do not have time to participate in a meeting (or organize a special-purpose call to review code together with other contributors), please understand up front that contributions may stall.
Even before you start working on a contribution, please feel free to join a call and discuss how you want to solve your problem or implement your feature. In the past, most contributions that were undertaken without any discussion up front required major changes before acceptance.
We try to reduce the time demands on reviewers by putting more responsibilities on the PR submitter. This does carry a risk of discouraging contributions, but without a "sponsor" organization for a change, the time available to review is the bottleneck in the process.
In sum: if you are interested in integrating your code into core OTP, a significant amount of the time you invest in OTP will need to be spent on collaboration, discussion, documentation, etc. and you will need to be available for regular meetings. You will need to take this into consideration in your budget and timeline.
We don't want to discourage innovation and experimentation, and want promising new features to be visible to other users, so we have also created a Sandbox system for fast-track review and inclusion in mainline OTP. Most code for a Sandbox feature must be located in its own package, and any code added to the core of OTP must be in conditional blocks controlled by a feature flag and disabled by default. This greatly simplifies and accelerates the review process, as requirements on the code outside core OTP will be much less stringent. Please see http://docs.opentripplanner.org/en/latest/SandboxExtension/ for more details.
If you don't have the time to participate in this process, the community is of course still interested in the new ideas and capabilities in your fork of OTP. Please do share them on the groups (mailing lists) where you may create awareness of your work and attract collaborators with more resources. The goal of mainline OTP is not to be everything to everyone, but rather to contain the most solid code relied upon daily by the primary OTP contributor organizations (as well as Sandbox features that have been cleanly isolated from the core system). So in a sense it's encouraged for people to work on special-purpose forks.
When creating and building on a pull request, please do the following:
- If possible, please discuss your proposed changes in advance before proceeding too far with development. There are often other plans to address the same problem, or at least other points of view and ideas. Coordinating with other OTP developers can avoid a lot of duplicated effort, conflict, and technical debt and make the review process a lot easier.
- Describe in detail the problem you are solving and any major design choices you have made. PR descriptions must clearly state how your changes work.
- Break large changes down into a series of smaller logical steps in separate PRs.
- Tie such series of PRs together with an "epic issue" that explains the overall plan.
- Use Github issue references ("addresses #12" etc.) to connect PRs and issues together.
- Consider squashing and rebasing to make the PR history easier to understand, eliminating extra " noise" commits like accidental changes to organization specific code, abandoned experiments, or reverted configuration changes.
In turn, in order to prevent OTP2 from turning into a " big-ball-of-mud" (https://en.wikipedia.org/wiki/Big_ball_of_mud) and ensure development does grind to a halt, the maintainers of the project will:
- Keep an eye out for features which are not core, and suggest that they be Sandbox features.
- Ask for example use cases for new functionality to make sure OTP is the right place to implement it (rather than some external component).
- Make sure the implementation avoids duplication and the addition of new layers and is encapsulated, requesting refactoring if necessary.
- Make sure non-functional characteristics (performance and memory usage) are maintained when features are added.
The vast majority of the work done by the core development team is now on OTP2 (the dev-2.x
branch) as opposed to OTP1 (the dev-1.x branch). Please
see http://docs.opentripplanner.org/en/latest/Version-Comparison/ for a discussion of the difference
between these two branches. At this point, OTP1 is essentially a legacy product that will receive
bug and stability fixes to the extent that they can be readily backported from OTP2 or that the
author of such patches can invest the effort to join a meeting and answer any questions about the
impact and design of their code.
There is a large base of existing deployments of OTP1, in both trip planning and academic research use. OTP2 is different in many ways from OTP1, and some features that were research prototypes or not actively maintained have been removed. We want to ensure long-term users can continue to rely on these OTP1-specific if needed. Therefore we cannot apply changes to OTP1 which pose any significant risk of introducing new bugs or behavior changes, as this will create additional maintenance or documentation work for which there is no budgeted developer time.