rustdoc: macros expanded from macros don't get their rules documented correctly

[remexre]

When writing a macro_rules! macro that expands to another macro_rules! macro, the Rustdoc shows the source-code tokens pre-outer-macro-expansion in the rules for the inner macro. I was expecting to see something like the expansion in trace_macros!(), which does have the post-expansion rules.

Meta

rustdoc --version --verbose:

rustdoc 1.53.0
binary: rustdoc
commit-hash: unknown
commit-date: unknown
host: x86_64-unknown-linux-gnu
release: 1.53.0
LLVM version: 12.0.1

[jyn514]

@remexre can you give an example of this? I don't know what the difference would be between pre- and post-expansion.

[remexre]

The example I have on hand is the result of expanding https://git.sr.ht/~remexre/ia/tree/691c22fb86e162f9b0360b03d987275134b66c64/item/engine/util.rs#L48 gets documented like:

I can make a minimized example tonight if that'd be more helpful.

[jyn514]

I can make a minimized example tonight if that'd be more helpful.

That would be great, thanks!

[remexre]

Okay, the following program:

macro_rules! foo {
    ($name:ident => $($body:tt)*) => { foo!([$], $name, $($body)*); };
    ([$dollar:tt], $name:ident, $($body:tt)*) => {
        #[macro_export]
        macro_rules! bar {
            ($dollar $name :tt) => { $($body)* };
        }
    };
}

foo!(msg => println!($msg));

fn main() {
    bar!("Hello, world!");
}

gets the bar macro documented as:

macro_rules! bar {
    ($dollar $name :tt) => { ... };
}

rather than as

macro_rules! bar {
    ($ msg :tt) => { ... };
}

[camelid]

This is fixed now, probably by #86282 (cc #45939).