macro fragment names are no longer idents

[durka]

This is a stable-to-beta regression, but it's such a weird thing to do that I don't know if it counts.

Consider the following code (playpen):

macro_rules! gen {
    ($name:ident ($($dol:tt $var:ident)*) $($body:tt)*) => {
        macro_rules! $name {
            ($($dol $var:ident)*) => {
                $($body)*
            }
        }
    }
}

The gen macro parses a macro argument spec by matching a dollar sign with $dol and the fragment name with $var. Then (in this toy example) it just regurgitates that adding :ident as the type of each fragment.

This works in 1.17, but fails when invoked in 1.18 and nightly with the message "expected identifier, found [the ident passed in for $var]", pointing at $var on line 4. All three channels work if $var:ident is changed to $var:tt on line 2.

[durka]

cc @jseyfried

[jseyfried]

I believe this is a duplicate of #41803; it should be fixed once #42005 lands.

[nagisa]

Now that #42005 has landed, this should be re-reproduced.

[durka]

It landed, but why is there no nightly?

[durka]

This was not fixed by #42005. It is still broken with rustc 1.19.0-nightly (0ed1ec9 2017-05-18).

[brson]

Still broken on beta too I guess?

[durka]

Yes, the code in the playpen still fails to compile on beta and nightly.

[nikomatsakis]

cc @Mark-Simulacrum -- it'd be great to know just what caused this problem. @jseyfried, are you going to have time to investigate?

[Mark-Simulacrum]

If I have a chance I'll run bisect-rust, also cc @est31 -- they have it working locally as well.

[Mark-Simulacrum]

Ran bisect: fe15119 - #40597.