Expected compile error because bad use of semicolon

[wilcus]

Actual result compile and output "bogus"

Code:
https://pastebin.mozilla.org/8844697

rustc 1.4.0-dev (7b7fc67 2015-08-13)

[jonas-schievink]

Code in question:

fn main(){
  if 4==4{;
    println!("bogus");
  }
}

The grammar docs indeed disallow a bare ;.

[alexcrichton]

triage: I-nominated

[alexcrichton]

There's a PR to fix this issue (#29215), but as it's a language change I wanted to circulate among the lang team to ensure that it's intended.

(fwiw I would personally consider this behavior fine, as shown by the fall out in the PR it's often convenient to rely on this in contexts like with macros)

[fhahn]

If this comes out as wontfix, I think it still would make sense to remove the trailing semicolons after the few function definitions. I would also be happy to update the documentation and the reference parser.

[nikomatsakis]

We discussed in the @rust-lang/lang and came to the conclusion that parsing an empty semicolon here is not a bug and we should not attempt to issue warnings or make it an error. In fact, most of us rather expected it to work, perhaps because of C precendent.

However, @nrc pointed out that a clippy lint might be suitable or -- perhaps better yet -- modifying rustfmt to drop such statements. I too would personally prefer to have rustfmt silently clean things up behind my back than to have to some lint nag me about it. :)

[nikomatsakis]

(Also, it seems like a case where being backwards incompatible just isn't really necessary.)

[fhahn]

Sure that makes perfect senes. @jonas-schievink do you remember where you found the grammar definition which said a bare semicolon should not be allowed? I could not find it.

[jonas-schievink]

I think I looked at http://doc.rust-lang.org/grammar.html#statements-and-expressions

[fhahn]

@jonas-schievink thanks Jonas, I've updated the docs.