I find the whole thing rather confusing.
rls mentions racer in the setup instructions but it isn't clear if it is actually required. rls needs rust-analysis (which I conflated with rust-analyzer, thinking they were the same thing).
Is rls deprecated in favor of rust-analyzer?
rust-analyzer isn't available on stable? Does that impact what toolchain I am using, or only what toolchain is needed to build rust-analyzer? Strike that, I thought it should be added as a component like rust-analysis. Trying to install via cargo produces a message that there is no binary to install for rust-analyzer.
Edit: Ok, I git cloned rust-analyzer and built it. I placed the executable in my path. Installed YouCompleteMe plugin for vim, which according to the rust-analyzer manual, should work out of the box. It doesn't seem to do anything at all. I'm wondering if the version of YouCompleteMe might be older than expected in the manual. It'd be helpful if documentation listed actual required versions of things.
Final edit: I gave up. Trying to get a newer YCM plugin led to needing a newer CMake. I've already wasted more time on this than any amount of semantic analysis and autocompletion would ever have saved me. I'm going back to my simple but efficient setup with rust.vim.