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::cfg_if::cfg_if![ if #[cfg(feature = "proc-macro-hygiene")]
{
#[cfg(any())]
mod objective {
macro_rules! as_bytes {(
$input_str_literal:expr
) => (
b"_"
)}
}
#[doc(hidden)]
#[proc_macro]
pub fn as_bytes (
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream
{
let input_expr = syn::parse_macro_input!(input as syn::Expr);
match input_expr {
// if the input expression already was a byte string literal,
// return it as is.
syn::Expr::Lit(
syn::ExprLit {
lit: syn::Lit::ByteStr(_),
..
}
) => proc_macro::TokenStream::from(quote::quote! {
input_expr
}),
// else if the input expression is a string literal, create a
// byte string literal out of its bytes.
syn::Expr::Lit(
syn::ExprLit {
lit: syn::Lit::Str(input_str_literal),
attrs: _,
}
) => {
proc_macro::TokenStream::from(
proc_macro::TokenTree::Literal(
proc_macro::Literal::byte_string(
input_str_literal.value().as_bytes()
)
)
)
},
// else, the macro was misused
_ => throw!(input_expr.span()=>
"expected a string literal (or a byte string literal)"
),
}
}
}
else
{
#[cfg(any())]
mod objective {
macro_rules! const_as_bytes {(
const $const_literal_name:ident = as_bytes!(
$input_str_literal:expr
);
) => (
const $const_literal_name: &[u8; _] = b"_";
)}
}
struct ConstAsBytes {
const_literal_name: syn::Ident,
input_str_literal: syn::Expr,
}
impl Parse for ConstAsBytes
{
fn parse (input: syn::parse::ParseStream) -> syn::parse::Result<Self>
{
macro_rules! parse_token {[$tt:tt] => (
input.parse::<syn::Token![$tt]>()?
)}
parse_token![ const ];
let const_literal_name: syn::Ident = input.parse()?;
parse_token![ = ];
input.parse::<kw::as_bytes>()?;
parse_token![ ! ];
let input_str_literal: syn::Expr = syn::group::
parse_parens(&input)?
.content
.parse()?
;
parse_token![ ; ];
Ok(ConstAsBytes {
const_literal_name,
input_str_literal,
})
}
}
#[proc_macro]
pub fn const_as_bytes (
input: proc_macro::TokenStream,
) -> proc_macro::TokenStream
{
let ConstAsBytes {
const_literal_name,
input_str_literal: input_expr,
} = syn::parse_macro_input!(input);
let expr_span = input_expr.span().clone();
let (bytes, attrs) = match input_expr {
// if the input expression already was a byte string literal,
// return it as is.
syn::Expr::Lit(
syn::ExprLit {
lit: syn::Lit::ByteStr(_),
..
}
) => return proc_macro::TokenStream::from(quote::quote! {
const #const_literal_name: &'static str = #input_expr;
}),
// else if the input expression is a string literal, extract the
// inner bytes (to create a byte string literal out of them).
syn::Expr::Lit(
syn::ExprLit {
lit: syn::Lit::Str(input_str_literal),
attrs,
}
) => (input_str_literal.value().into_bytes(), attrs),
// else, the macro was misused
_ => throw!(input_expr.span()=>
"expected a string literal (or a byte string literal)"
),
};
let len = syn::Expr::
Lit(syn::ExprLit {
attrs: vec![],
lit: syn::Lit::Int(syn::LitInt::new(
// value
bytes.len() as u64,
// suffix
syn::IntSuffix::Usize,
// Span
expr_span.clone(),
))
})
;
let bytes = syn::Expr::
Lit(syn::ExprLit {
attrs,
lit: syn::Lit::ByteStr(syn::LitByteStr::new(
// value
&bytes,
// Span
expr_span.clone(),
))
})
;
proc_macro::TokenStream::from(quote::quote! {
const #const_literal_name: &'static [u8; #len] = #bytes;
})
}
}];