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// the code is from THE BOOK
// https://doc.rust-lang.org/book/ch19-06-macros.html#how-to-write-a-custom-derive-macro
// but I forgot to append `!` to `stringify`, in the `hello_macro_derive/src/lib.rs/impl_hello_macro`.
// However, the `hello_macro_derive` crate was built successfully, but the `pancake` crate,
// which uses the derive-macro, was built failed with a confusing diagnostic message.
//
// pancake/src/main.rs
//
use hello_macro::HelloMacro;
use hello_macro_derive::HelloMacro;
#[derive(HelloMacro)]
struct Pancake;
fn main() {
Pancake::hello_macro();
}
//
// hello_macro/hello_macro_derive/src/lib.rs
//
use proc_macro::TokenStream;
use quote::quote;
use syn;
#[proc_macro_derive(HelloMacro)]
pub fn hello_macro_derive(input: TokenStream) -> TokenStream {
let ast = syn::parse(input).unwrap();
impl_hello_macro(&ast)
}
fn impl_hello_macro(ast: &syn::DeriveInput) -> TokenStream {
let name = &ast.ident;
let gen = quote! {
impl HelloMacro for #name {
fn hello_macro() {
println!("Hello Macro! This is {}", stringify(#name))
}
}
};
gen.into()
}Current output
error[E0423]: expected function, found macro `stringify`
--> src/main.rs:4:10
|
4 | #[derive(HelloMacro)]
| ^^^^^^^^^^ not a function
|
= note: this error originates in the derive macro `HelloMacro` (in Nightly builds, run with -Z macro-backtrace for more info)
help: use `!` to invoke the macro
|
4 | #[derive(HelloMacro!)]
| +
For more information about this error, try `rustc --explain E0423`.
error: could not compile `pancakes` due to previous errorDesired output
`hello_macro_derive` crate should be failed to build due to `stringify`, since this does not pass the compilation in the normal crate.Rationale and extra context
No response
Other cases
No response
Anything else?
No response