// SPDX-License-Identifier: Apache-2.0 OR MIT use std::fmt::Display; use proc_macro2::TokenStream;use quote::quote_spanned;use syn::{spanned::Spanned, Error}; pub(crate) struct DiagCtxt(TokenStream);pub(crate) struct ErrorGuaranteed(()); impl DiagCtxt {    pub(crate) fn error(&mut self, span: impl Spanned, msg: impl Display) -> ErrorGuaranteed {        let error = Error::new(span.span(), msg);        self.0.extend(error.into_compile_error());        ErrorGuaranteed(())    }     pub(crate) fn warn(&mut self, span: impl Spanned, msg: impl Display) {        // Have the message start on a new line for visual clarity.        let msg = format!("\n{}", msg);        self.0.extend(quote_spanned!(span.span() =>            // Approximate using deprecated warning while `proc_macro_diagnostic` is unstable.            const _: () = {                #[deprecated = #msg]                const fn warn() {}                warn();            };        ));    }     pub(crate) fn with(        fun: impl FnOnce(&mut DiagCtxt) -> Result<TokenStream, ErrorGuaranteed>,    ) -> TokenStream {        let mut dcx = Self(TokenStream::new());        match fun(&mut dcx) {            Ok(mut stream) => {                stream.extend(dcx.0);                stream            }            Err(ErrorGuaranteed(())) => dcx.0,        }    }}