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//@ force-host
//@ no-prefer-dynamic
#![crate_type = "proc-macro"]
#![feature(proc_macro_diagnostic, proc_macro_span, proc_macro_def_site)]
extern crate proc_macro;
use proc_macro::{TokenStream, TokenTree, Span, Diagnostic};
fn parse(input: TokenStream) -> Result<(), Diagnostic> {
let mut count = 0;
let mut last_span = Span::def_site();
for tree in input {
let span = tree.span();
if count >= 3 {
return Err(span.error(format!("expected EOF, found `{}`.", tree))
.span_note(last_span, "last good input was here")
.help("input must be: `===`"))
}
if let TokenTree::Punct(ref tt) = tree {
if tt.as_char() == '=' {
count += 1;
last_span = span;
continue
}
}
return Err(span.error(format!("expected `=`, found `{}`.", tree)));
}
if count < 3 {
return Err(Span::def_site()
.error(format!("found {} equal signs, need exactly 3", count))
.help("input must be: `===`"))
}
Ok(())
}
#[proc_macro]
pub fn three_equals(input: TokenStream) -> TokenStream {
if let Err(diag) = parse(input) {
diag.emit();
return TokenStream::new();
}
"3".parse().unwrap()
}
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