semicolon check in macro needs improving

[bombless]

https://play.rust-lang.org/?gist=9aca9a98b74f8a4522df7b0d16c8340e&version=beta&backtrace=0&run=1

I think the warning message here is not intentional.

[TimNN]

I'm pretty sure the warning message works as intended:

The first macro invocation (own!(a, b);) expands to own!(@a) own!(@b) which, if written in normal rust code, would produce a hard error. This was previously accepted by the compiler, but now triggers the warning introduced in #34660.

[bombless]

Hmm then the warning should be turned into an hard error now, I guess, thanks @TimNN

[bombless]

May I ask, why is the semicolon after to_owned() dropped in the (@$x:ident) => { let $x = $x.to_owned(); }; part?
I figure it might be the root case that bug existed, which I don't really understand.

[TimNN]

I don't think that semicolon is dropped. However, as far as I know, macros are expanded in multiple steps: own!(a, b); is expanded to own!(@a) own!(@b), which then parsed again and expanded to let a = ...; let b = ...; The warning is reported for the intermediate expansion, not the final one: the semicolons added by the (@$x:ident) rule don't exist yet.