https://rustc-dev-guide.rust-lang.org/building/suggested.html#neovim describes three ways to use neovim.

1. Using neoconf.nvim and the vscode settings.
2. using coc.nvim
3. using the manual config.

Option 1 mostly seem to work just fine, except neovim not recognizing or replacing ${workspaceFolder}
(see also) #2259 (comment)
I ended up replacing it with the absolute path. I'm not super experienced with these configs, so not sure if neovim has another name for it, if we should ask Neovim devs to add support, or (probably a good addition either way) add a note to the docs which tells users to use the absolute path.

At least option 3. also defines a function to recognize and handle the workspacefolder, but it's not clear that users have to handle it manually when using neoconf.