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Chandler Carruthandjosh11b
da7533ae7f
This should also unblock our switch to C++20 and other improvements. There are three core parts of the change -- 1) Updating our infrastructure to fetch and find Clang-16. 2) Updating our documentation to reflect this and help folks with any system issues they encounter. The infrastructure change is unfortunately tricky. We can't get Clang 16 easily on GitHub's runner images, and in the past we've had persistent problems with flakiness when our actions download this much during their runs. Due to the flakiness, we've previously removed all downloading of dependencies outside of Bazel itself, and added retry loops around Bazel specifically to overcome flaky downloads. This change tries to address these problems by populating the Clang and LLVM toolchain in a place that we can then cache using the built-in GitHub action caching infrastructure. This seems like by far the least likely to flake way of downloading extra things into our runs. And since these are relatively slow moving dependencies, we should populate this cache very, very rarely. For Linux, this downloads the binary release artifact from GitHub, prunes out large parts of it that we don't need, and then caches this as a local toolchain. This proves both small and fast. For macOS, this uses a trick to cache the destination of Homebrew installs. It unfortunately caches the *entire* Homebrew installation though, and so it also goes to some lengths to prune and minimize how much is installed from Homebrew. The result is "only" a 2gb cache image. Because of the size and slower download and filesystem, the macOS runs see a 1 - 2 minute slowdown. We might extend the Linux infrastructure here usefully if we want to test multiple LLVM versions. We might also extend the macOS version to get a cheaper way to prune parts of the system and free up disk space, or to cache other Homebrew installed tools if needed. Last but not least, this brought to the forefront an issue with our C++ toolchain integration which relied on a specific CMake build option being set in the LLVM toolchain install. This option isn't used in the official release artifacts. Instead, switch to a more robust approach to linking libc++abi statically that shouldn't have these problems. Beyond the infrastructure changes, this also updates the documentation to reflect requiring Clang 16 or newer, and adds some extra tips for folks that are missing this. The documentation is also updated to address a problem with getting the right libc++abi files installed to support the more robust linking strategy. This may reduce the problems we've seen in the past around libc++abi and linking on other Linux distros as well. --------- Co-authored-by: josh11b <josh11b@users.noreply.github.com>
Project
This directory contains project-related documentation for Carbon. Information about how the project works, goals, and community information belong here.
- Goals, and principles derived from those goals
- Roadmap and the process for updating it
- Carbon's process for evolution and governance
- Groups used for contacting key contributors and determining access
- Contributing to Carbon:
- Tools used when contributing to Carbon
- Style guides for language design and C++ code
- How Carbon does code review
- Trunk-based pull-request GitHub workflow used by Carbon