I use include_str!()
to import the string from a file and pass it into a proc_marco, but it does not work. I get an expected string literal
error. Here is my code:
macro_rules! ptcl_layer {
() => {
include_str!("tcp_to_msg.layer")
};
}
pub static TEMPLETE: &'static str = ptcl_layer!();
pub static TEMPLETE_HEADER: &'static str = get_protocol_layer_header!(ptcl_layer!());
pub static TEMPLETE_END: &'static str = get_protocol_layer_end!(ptcl_layer!());
#[proc_macro]
pub fn get_protocol_layer_header(_s: TokenStream) -> TokenStream {
let total_str = parse_macro_input!(_s as LitStr).value();
let header = total_str.lines().next().unwrap();
let header = header.replace("${.LEN}\n", "");
let output = quote::quote! {
#header
};
TokenStream::from(output)
}
#[proc_macro]
pub fn get_protocol_layer_end(_s: TokenStream) -> TokenStream {
let input = parse_macro_input!(_s as LitStr);
let input = input.value();
let last_line = input.lines().last().unwrap_or("");
let output = quote::quote! {
#last_line
};
TokenStream::from(output)
}
The full error msg:
error: expected string literal
--> src/controller/mod.rs:16:71
|
16 | pub static TEMPLETE_HEADER: &'static str = get_protocol_layer_header!(ptcl_layer!());
| ^^^^^^^^^^
And the *.layer like:
<? lines: ${.LEN}
${.CONTENT}
<? end
I also tried another version of the code:
#[proc_macro]
pub fn get_protocol_layer_header(_s: TokenStream) -> TokenStream {
let total_str = _s.to_string();
let header = total_str.lines().next().unwrap();
let header = header.replace("${.LEN}\n", "");
header.parse().unwrap()
}
#[proc_macro]
pub fn get_protocol_layer_end(_s: TokenStream) -> TokenStream {
let total_str = _s.to_string();
let last_line = total_str.lines().last().unwrap_or("");
last_line.parse().unwrap()
}
But it returned the original text without any processing.
As eqqyal noted, by default macros are evaluated outside in, but when some expression will result in a literal, like in your case, you can invert that using the unstable TokenStream::expand_expr
:
at the top of your_macros/src/lib.rs
:
#![feature(proc_macro_expand)]
in your definitions that take a LitStr
insert the following:
#[proc_macro]
pub fn get_protocol_layer_header(input: TokenStream) -> TokenStream {
let input = input.expand_expr().unwrap();
let total_str = parse_macro_input!(input as LitStr).value();
// …
This is something the outermost macros you want to use must accept so if you can't change the definiton of get_protocol_layer_header
and similar, or can't use nightly you'd have to work around it and insert the corresponding string literals with a build.rs
srcipt.