There's something fundamentally wrong with requirement to run compiler to get navigation/completion/etc.
Large C++ (and Rust, if you include rustc) projects (which need a Code Analyzer most, compared to small projects) I worked with often had their own bespoke build systems that required preliminary configuration, required options to pass, generated code from DSLs, lacked the "just build" command, were possibly too slow to invoke them automatically. And without that build system you cannot run the build or invoke compiler.
In this case tools using heuristics like racer, VSCode C++ plugins, ctags, whatever, more or less work and give acceptable results.
At the same time RLS that needs to run the build just plain gives up on rustc codebase.