src/test/ui/proc-macro/auxiliary/cond_plugin.rs

   1 // force-host
   2 // no-prefer-dynamic
   3
   4 #![crate_type = "proc-macro"]
   5 #![feature(proc_macro_quote)]
   6
   7 extern crate proc_macro;
   8
   9 use proc_macro::*;
  10
  11 #[proc_macro]
  12 pub fn cond(input: TokenStream) -> TokenStream {
  13     let mut conds = Vec::new();
  14     let mut input = input.into_iter().peekable();
  15     while let Some(tree) = input.next() {
  16         let cond = match tree {
  17             TokenTree::Group(tt) => tt.stream(),
  18             _ => panic!("Invalid input"),
  19         };
  20         let mut cond_trees = cond.clone().into_iter();
  21         let test = cond_trees.next().expect("Unexpected empty condition in `cond!`");
  22         let rhs = cond_trees.collect::<TokenStream>();
  23         if rhs.is_empty() {
  24             panic!("Invalid macro usage in cond: {}", cond);
  25         }
  26         let is_else = match test {
  27             TokenTree::Ident(ref word) => &*word.to_string() == "else",
  28             _ => false,
  29         };
  30         conds.push(if is_else || input.peek().is_none() {
  31             quote!({ $rhs })
  32         } else {
  33             quote!(if $test { $rhs } else)
  34         });
  35     }
  36
  37     conds.into_iter().flat_map(|x| x.into_iter()).collect()
  38 }