1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
|
#![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()
}
|
