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#![feature(proc_macro_diagnostic, proc_macro_span)]
extern crate proc_macro;
use proc_macro::{TokenStream, TokenTree, Span, Diagnostic};
fn parse(input: TokenStream) -> Result<(), Diagnostic> {
if let Some(TokenTree::Literal(lit)) = input.into_iter().next() {
let mut spans = vec![];
let string = lit.to_string();
for hi in string.matches("hi") {
let index = hi.as_ptr() as usize - string.as_ptr() as usize;
let subspan = lit.subspan(index..(index + hi.len())).unwrap();
spans.push(subspan);
}
if !spans.is_empty() {
Err(Span::call_site().error("found 'hi's").span_note(spans, "here"))
} else {
Ok(())
}
} else {
Err(Span::call_site().error("invalid input: expected string literal"))
}
}
#[proc_macro]
pub fn subspan(input: TokenStream) -> TokenStream {
if let Err(diag) = parse(input) {
diag.emit();
}
TokenStream::new()
}
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