I'll cite what Lukas said on this forum and rust-lang/rust-analyzer#15452: proc macros that don't consume inputs and avoiding erroring out would go a long way in making rust-analyzer behave nicely in the face of custom syntax.
For function-like, JSX-style macros—which seem to be the majority of function-like macros where the lack of tooling support is most acutely felt?—I'm not confident in any general solution that I might propose.