48 lines
1.6 KiB
Rust
48 lines
1.6 KiB
Rust
// Copyright 2016 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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#![crate_type = "proc-macro"]
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#![feature(proc_macro, proc_macro_non_items)]
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extern crate proc_macro;
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use proc_macro::*;
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#[proc_macro]
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pub fn cond(input: TokenStream) -> TokenStream {
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let mut conds = Vec::new();
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let mut input = input.into_iter().peekable();
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while let Some(tree) = input.next() {
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let cond = match tree {
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TokenTree::Group(tt) => tt.stream(),
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_ => panic!("Invalid input"),
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};
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let mut cond_trees = cond.clone().into_iter();
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let test = cond_trees.next().expect("Unexpected empty condition in `cond!`");
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let rhs = cond_trees.collect::<TokenStream>();
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if rhs.is_empty() {
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panic!("Invalid macro usage in cond: {}", cond);
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}
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let is_else = match test {
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TokenTree::Ident(word) => &*word.to_string() == "else",
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_ => false,
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};
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conds.push(if is_else || input.peek().is_none() {
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quote!({ $rhs })
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} else {
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quote!(if $test { $rhs } else)
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});
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}
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conds.into_iter().flat_map(|x| x.into_iter()).collect()
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}
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