57 lines
1.6 KiB
Rust
57 lines
1.6 KiB
Rust
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// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// no-prefer-dynamic
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#![feature(proc_macro)]
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#![crate_type = "proc-macro"]
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extern crate proc_macro;
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use proc_macro::{TokenStream, TokenNode, 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::default();
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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 TokenNode::Op('=', _) = tree.kind {
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count += 1;
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} else {
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return Err(span.error(format!("expected `=`, found `{}`.", tree)));
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}
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last_span = span;
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}
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if count < 3 {
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return Err(Span::default()
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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::empty();
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}
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"3".parse().unwrap()
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}
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