58 lines
1.8 KiB
Rust
58 lines
1.8 KiB
Rust
use crate::error::{Error, Result};
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use proc_macro::{Ident, Span, TokenStream, TokenTree};
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use std::iter;
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#[derive(PartialOrd, PartialEq)]
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enum Qualifiers {
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None,
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Async,
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Unsafe,
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Extern,
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Abi,
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}
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impl Qualifiers {
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fn from_ident(ident: &Ident) -> Self {
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match ident.to_string().as_str() {
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"async" => Qualifiers::Async,
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"unsafe" => Qualifiers::Unsafe,
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"extern" => Qualifiers::Extern,
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_ => Qualifiers::None,
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}
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}
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}
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pub(crate) fn insert_const(input: TokenStream, const_span: Span) -> Result<TokenStream> {
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let ref mut input = crate::iter::new(input);
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let mut out = TokenStream::new();
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let mut qualifiers = Qualifiers::None;
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let mut pending = Vec::new();
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while let Some(token) = input.next() {
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match token {
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TokenTree::Ident(ref ident) if ident.to_string() == "fn" => {
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let const_ident = Ident::new("const", const_span);
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out.extend(iter::once(TokenTree::Ident(const_ident)));
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out.extend(pending);
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out.extend(iter::once(token));
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out.extend(input);
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return Ok(out);
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}
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TokenTree::Ident(ref ident) if Qualifiers::from_ident(ident) > qualifiers => {
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qualifiers = Qualifiers::from_ident(ident);
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pending.push(token);
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}
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TokenTree::Literal(_) if qualifiers == Qualifiers::Extern => {
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qualifiers = Qualifiers::Abi;
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pending.push(token);
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}
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_ => {
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qualifiers = Qualifiers::None;
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out.extend(pending.drain(..));
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out.extend(iter::once(token));
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}
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}
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}
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Err(Error::new(const_span, "only allowed on a fn item"))
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}
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