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use proc_macro::TokenStream;
use proc_macro2::TokenStream as TokenStream2;
use quote::quote;
use syn::parse::{Parse, ParseStream};
use syn::{Ident, Token};
/// Parsed input for `r_println!` and `r_print!`.
///
/// Two forms:
/// - `(ident, format_args...)` — explicit buffer
/// - `(format_args...)` — implicit `__render_result_buffer`
enum PrintInput {
Explicit { dst: Ident, args: TokenStream2 },
Implicit { args: TokenStream2 },
}
impl Parse for PrintInput {
fn parse(input: ParseStream) -> syn::Result<Self> {
// Peek: if the next token is an ident followed by a comma, it's the explicit form
if input.peek(Ident) && input.peek2(Token![,]) {
let dst: Ident = input.parse()?;
let _comma: Token![,] = input.parse()?;
let args: TokenStream2 = input.parse()?;
Ok(PrintInput::Explicit { dst, args })
} else {
let args: TokenStream2 = input.parse()?;
Ok(PrintInput::Implicit { args })
}
}
}
fn expand_print(input: TokenStream, method: &str) -> TokenStream {
let parsed: PrintInput = match syn::parse(input) {
Ok(p) => p,
Err(e) => return e.to_compile_error().into(),
};
let method_ident = Ident::new(method, proc_macro2::Span::call_site());
let expanded = match parsed {
PrintInput::Explicit { dst, args } => {
quote! {
#dst.#method_ident(format!(#args))
}
}
PrintInput::Implicit { args } => {
quote! {
__render_result_buffer.#method_ident(format!(#args))
}
}
};
expanded.into()
}
pub(crate) fn r_println(input: TokenStream) -> TokenStream {
expand_print(input, "println")
}
pub(crate) fn r_print(input: TokenStream) -> TokenStream {
expand_print(input, "print")
}
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