Function get_proc_macros 

pub fn get_proc_macros(
    target: &Target,
    path: &Path,
    metadata_loader: &dyn MetadataLoader,
    cfg_version: &'static str,
) -> Result<Vec<(Client, ProcMacroKind)>>

A function to fetch about all macros inside a proc-macro crate.

Used by rust-analyzer-proc-macro-srv.