Getting Involved with the Clang Project

Once you have checked out and built clang and played around with it, you might be wondering what you can do to make it better and contribute to its development. Alternatively, maybe you just want to follow the development of the project to see it progress.

Contribute

See the hacking document for information on how to author patches.

Follow what's going on

Clang is a subproject of the LLVM Project and has a Discourse forum and mailing list:

• Clang Frontend Discourse forum - This forum is for discussions related to Clang (questions and answers, design discussions, RFCs, etc).
• Discord chat - Real-time chat for discussions related to Clang (primarily for questions and answers).
• Regular meetings are held on the first and third Wednesday of each month to discuss C and C++ standards-related activities happening within the Clang community. These meetings are a way to coordinate efforts between implementers and provide updates on how standards activities are going. Meeting agendas and minutes are available here.
• Clang office hours - People within the community hold dedicated office hours at different points during the month, which is a great way opportunity for getting questions answered, having more in-depth design discussions, or learning about what's going on in the community in general.
• cfe-commits - Historical record of commits to Clang and contains early community patch review commentary.

The most common way to talk with other developers on the project is through the Clang Frontend Discourse forum . The clang forum is a very friendly place and we welcome newcomers. The forum is archived so you can browse through previous discussions or follow development on the web if you prefer.

If you're looking for something to work on, check out our Open Projects page or look through the LLVM bug tracker.

Contributing Extensions to Clang

Clang is designed to support experimentation, allowing programmers to easily extend the compiler to support great new language features and tools. At some point, the authors of these extensions may propose that the extensions become a part of Clang itself, to benefit the whole Clang community. However, extensions (particularly language extensions) have long-term maintenance costs for Clang. The benefits of the extension need to be evaluated against these costs. The Clang project uses the following criteria for this evaluation:

1. Evidence of a significant user community: This is based on a number of factors, including an existing user community, the perceived likelihood that users would adopt such a feature if it were available, and any secondary effects that come from, e.g., a library adopting the feature and providing benefits to its users.
2. A specific need to reside within the Clang tree: There are some extensions that would be better expressed as a separate tool, and should remain as separate tools even if they end up being hosted as part of the LLVM umbrella project.
3. A specification: The specification must be sufficient to understand the design of the feature as well as interpret the meaning of specific examples. The specification should be detailed enough that another compiler vendor could implement the feature.
4. Representation within the appropriate governing organization: For extensions to a language governed by a standards committee (C, C++, OpenCL), the extension itself must have an active proposal and proponent within that committee and have a reasonable chance of acceptance. Clang should drive the standard, not diverge from it. This criterion does not apply to all extensions, since some extensions fall outside of the realm of the standards bodies.
5. A long-term support plan: increasingly large or complex extensions to Clang need matching commitments to supporting them over time, including improving their implementation and specification as Clang evolves. The capacity of the contributor to make that commitment is as important as the commitment itself.
6. A high-quality implementation: The implementation must fit well into Clang's architecture, follow LLVM's coding conventions, and meet Clang's quality standards, including diagnostics and complete AST representations. This is particularly important for language extensions, because users will learn how those extensions work through the behavior of the compiler.
7. A test suite: Extensive testing is crucial to ensure that the language extension is not broken by ongoing maintenance in Clang. The test suite should be complete enough that another compiler vendor could conceivably validate their implementation of the feature against it.
8. A support story for other impacted projects within the monorepo: If the extension can impact other parts of the project (libc++, lldb, compiler-rt, etc), the proposal needs to document the impact for these projects to fully support the extension and what level of support is expected. The impacted project communities need to agree with that plan.

The Clang community uses an RFC process to evaluate potential extensions for inclusion in the tool. First, write a post in the Clang Frontend category of Discourse. The title should include [RFC] so it is clear that it is a proposed change. The post should have detailed information about the change itself, the motivation for needing the change, how it addresses the criteria listed above, and any other relevant details the community should be aware of.

The community will discuss the proposal in Discourse, asking questions about the proposal to improve their understanding and giving support or dissent for the idea. Eventually, consensus will be determined as to whether the proposal should proceed or be rejected. If a proposal receives little or no feedback, that typically means that the proposal is rejected due to lack of interest.

Sometimes, a consensus position is unclear and the proposal author will need additional guidance on what next steps to take. In such a case, the Clang Area Team may get involved. The Clang Area Team secretary will proactively look for RFCs that appear to not have a clear path forward to add them to the team's agenda. If anyone would like to put an RFC onto the team's agenda explicitly, they can tag any one of the Clang Area Team members in a comment on the RFC to get their attention. The area team will host a meeting to discuss the RFC and determine next steps for the proposal. In the event no clear community consensus position seems likely to ever form, the Clang Area Team will make a final judgement call on whether the RFC will proceed or not.