Trailing semicolon silently ignored in expr macro

[mahkoh]

fn main() {
    macro_rules! a {
        ($e:expr) => { $e; }
    }
    a!(true)
}

Error: Expected (), found bool

But:

fn main() {
    macro_rules! a {
        ($e:expr) => { $e; }
    }
    a!(true);  // <-- semicolon
}

does not warn that the ; is ignored.

So either

• there should be a warning that the ; has no effect in the macro, or
• the ; inside the macro should turn the expression into ().

[rozbb]

I'm not sure there should be a warning for use of a semicolon in an expression expansion. The problem is fixed when you write ($e: expr) => {{ $e; }} which indicates a block expansion.

So the semicolon is silently ignored, but putting something after it throws a helpful error: ($e:expr) => { $e; blahblah } gives the error "macro expansion ignores token blahblah and any following".

[jseyfried]

cc me