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Diffstat (limited to '')
-rw-r--r-- | third_party/rust/rustversion/src/constfn.rs | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/third_party/rust/rustversion/src/constfn.rs b/third_party/rust/rustversion/src/constfn.rs new file mode 100644 index 0000000000..0e50c03969 --- /dev/null +++ b/third_party/rust/rustversion/src/constfn.rs @@ -0,0 +1,58 @@ +use crate::error::{Error, Result}; +use proc_macro::{Ident, Span, TokenStream, TokenTree}; +use std::iter; + +#[derive(PartialOrd, PartialEq)] +enum Qualifiers { + None, + Async, + Unsafe, + Extern, + Abi, +} + +impl Qualifiers { + fn from_ident(ident: &Ident) -> Self { + match ident.to_string().as_str() { + "async" => Qualifiers::Async, + "unsafe" => Qualifiers::Unsafe, + "extern" => Qualifiers::Extern, + _ => Qualifiers::None, + } + } +} + +pub(crate) fn insert_const(input: TokenStream, const_span: Span) -> Result<TokenStream> { + let ref mut input = crate::iter::new(input); + let mut out = TokenStream::new(); + let mut qualifiers = Qualifiers::None; + let mut pending = Vec::new(); + + while let Some(token) = input.next() { + match token { + TokenTree::Ident(ref ident) if ident.to_string() == "fn" => { + let const_ident = Ident::new("const", const_span); + out.extend(iter::once(TokenTree::Ident(const_ident))); + out.extend(pending); + out.extend(iter::once(token)); + out.extend(input); + return Ok(out); + } + TokenTree::Ident(ref ident) if Qualifiers::from_ident(ident) > qualifiers => { + qualifiers = Qualifiers::from_ident(ident); + pending.push(token); + } + TokenTree::Literal(_) if qualifiers == Qualifiers::Extern => { + qualifiers = Qualifiers::Abi; + pending.push(token); + } + _ => { + qualifiers = Qualifiers::None; + out.extend(pending.drain(..)); + out.extend(iter::once(token)); + } + } + } + + Err(Error::new(const_span, "only allowed on a fn item")) +} |