[llvm-dev] [RFC] [CMake] Removing support for LLVM_TOOL_ CMake cache variables (original) (raw)

Dan Liew via llvm-dev llvm-dev at lists.llvm.org
Wed Feb 6 04:09:50 PST 2019

Dropping support for in-tree builds after the monorepo migration is an interesting question, because in theory people could still nest the read-only single project mirrors (assuming those end up coming to fruition) in the same style. I think it'd be good to reduce the number of supported configurations and clean up our build; I'm adding Chris to see what he thinks.

When we complete the migration to the monorepo my suggestion would be to drop the special support we have today for in-tree builds. Instead expose CMake cache variables that tell the CMake build where to find the projects' source trees. By default they would be initialised to their location in the monorepo but a user could pick any location. I think this approach is better because it's more general (there is a single source of truth for the location of a projects source tree), and is general enough to allow the user to place projects, in tree if they really want to.

This generality would also allow a user to build LLVM and other projects with each project potentially at different revisions. Git worktrees (i.e. create a worktree per project with a unique branch name to avoid doing a git clone per project) could potentially make this a bit easier too. It's a bit clunky but most people probably shouldn't be mixing revisions anyway.

Thanks, Dan.

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