Hi, I am currently trying to use a procedural macro as a custom inner attribute to apply my macro to every function in my crate without manually adding it.

I am first trying to use a noop procedural macro which does not modify anything. This is the implementation of that macro--

#[proc_macro_attribute]
pub fn noop(_args: TokenStream, input: TokenStream) -> TokenStream {
 let f = parse_macro_input!(input as ItemFn);
 quote!(#f).into()
}

Then, in my main crate, I added this to the top of main.rs--

#![feature(custom_inner_attributes)]
#![my_macro_crate::noop]

In main.rs, there is my main function, and a few other functions to test if the macro will work when I use my real macro.

After running cargo +nightly run, I receive 4 errors--

error: expected square brackets
--> main.rs:1:1
(it also red highlights the end of the file)

error: #[panic_handler] function required, but not found
error: unwinding panics are not supported without std

error: main function not found

Is it expected for any procedural macros to work as custom inner attributes? Since this NoOp macro does not compile, is there something I did incorrectly in my setup?

Also, when I run cargo +nightly expand > output.rs, the only error is "expected square brackets", which also underlines the end of the file. And the only contents of output.rs is

#![feature(prelude_import)]

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I am using a nightly build of rustc, installed with cargo a few days ago.