77 lines
2.1 KiB
Rust
77 lines
2.1 KiB
Rust
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// Copyright 2012-2015 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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#![crate_type = "rustc-macro"]
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#![feature(rustc_macro, rustc_macro_lib)]
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extern crate syn;
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#[macro_use]
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extern crate quote;
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extern crate rustc_macro;
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use rustc_macro::TokenStream;
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use syn::Body::Enum;
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use syn::VariantData::Unit;
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#[rustc_macro_derive(FromPrimitive)]
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pub fn from_primitive(input: TokenStream) -> TokenStream {
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let source = input.to_string();
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let ast = syn::parse_macro_input(&source).unwrap();
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let name = &ast.ident;
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let variants = match ast.body {
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Enum(ref variants) => variants,
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_ => {
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panic!("`FromPrimitive` can be applied only to the enums, {} is not an enum",
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name)
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}
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};
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let mut idx = 0;
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let variants: Vec<_> = variants.iter()
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.map(|variant| {
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let ident = &variant.ident;
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match variant.data {
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Unit => (),
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_ => {
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panic!("`FromPrimitive` can be applied only to unitary enums, {}::{} is either struct or tuple", name, ident)
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},
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}
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if let Some(val) = variant.discriminant {
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idx = val.value;
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}
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let tt = quote!(#idx => Some(#name::#ident));
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idx += 1;
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tt
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})
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.collect();
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let res = quote! {
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#ast
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impl ::num::traits::FromPrimitive for #name {
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fn from_i64(n: i64) -> Option<Self> {
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Self::from_u64(n as u64)
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}
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fn from_u64(n: u64) -> Option<Self> {
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match n {
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#(variants,)*
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_ => None,
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}
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}
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}
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};
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res.to_string().parse().unwrap()
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}
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