Rustdoc generate wrong doc for declarative macro generated by derive macro.

[Evian-Zhang]

First, write a derive macro which generates a declarative macro:

use quote::quote;

#[proc_macro_derive(MyDeriveMacro)]
pub fn derive_my_derive_macro(item: proc_macro::TokenStream) -> proc_macro::TokenStream {
    proc_macro::TokenStream::from(quote! {
        #[macro_export]
        macro_rules! my_generated_macro {
            ($my_macro_parameter: expr) => {};
        }
    })
}

Then in another crate, import this derive macro and use it:

#[derive(MyDeriveMacro)]
struct MyStruct {}

Then use

cargo doc

to generate the docs.

The doc for my_generated_macro should be

macro_rules! my_generated_macro {
    ($my_macro_parameter: expr) => {};
}

But instead, it turns out

macro_rules! my_generated_macro {
    MyDeriveMacro => {};
}

This is very confusing, since the parameters of the generated declarative macro are all missing, and instead is name of the derive macro which generated it.

Meta

rustc --version --verbose:

rustc 1.48.0 (7eac88abb 2020-11-16)
binary: rustc
commit-hash: 7eac88abb2e57e752f3302f02be5f3ce3d7adfb4
commit-date: 2020-11-16
host: x86_64-apple-darwin
release: 1.48.0
LLVM version: 11.0

[ThePuzzlemaker]

Expansion via cargo +nightly rustc -- -Zunpretty=expanded shows that this is not an expansion bug or bug in the code:

#[macro_export]
macro_rules! my_generated_macro { ($ my_macro_parameter : expr) => { } ; }

[ThePuzzlemaker]

@rustbot claim

[ThePuzzlemaker]

Also confirmed on latest nightly:

rustc 1.50.0-nightly (11c94a197 2020-12-21)
binary: rustc
commit-hash: 11c94a197726b6a981828cb1837d7c3eed1b841d
commit-date: 2020-12-21
host: x86_64-unknown-linux-gnu
release: 1.50.0-nightly