Clang is the C++ compiler used by hundreds of millions of developers every day, yet most of those developers have never looked inside it. The codebase can feel intimidating, with millions of lines of C++, an unfamiliar architecture, and a review process with its own customs. But once you know the map, contributing is surprisingly accessible.
This session is a live, code-first walkthrough of the full contribution cycle for Clang. Starting from a clone of the LLVM monorepo, we will configure a development build, locate the right subsystem for a real reported bug, write a regression test, fix the bug, and verify the fix. We will then extend that foundation to implement a small but complete language feature: adding a new diagnostic, walking through Sema, the AST, and the diagnostic engine as we go. Every step attendees see on screen can be replicated on their own laptops during and after the session.
Attendees will leave with a mental model of Clang's layered architecture (driver, frontend, Sema, CodeGen), a workflow for finding the code responsible for any given compiler behavior, and enough familiarity with the test infrastructure and review process to open their first pull request.
