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