Trailing + in bounds are allowed

[qnighy]

Current parser allows ty/lt bounds have extra +. However, the comments on the parser suggest they shouldn't be allowed. grammar.md also suggests they shouldn't.

Expected behavior

Both the first and second lines should lead to parse error.

fn f<'a>() where 'a: 'a + {}
fn g<'a, X>() where X: 'a + {}
fn main() {
}

Current behavior

The current stable and nightly compilers allow the above code.

Meta

Tested on Rust Playground.

stable

rustc 1.16.0 (30cf806ef 2017-03-10)

nightly

rustc 1.18.0-nightly (50c186419 2017-04-06)

[petrochenkov]

This works as expected, see #39158 for the discussion.

However, the comments on the parser suggest they shouldn't be allowed.
grammar.md also suggests they shouldn't.

I forgot to update the comment :(
grammar.md also seems to be largely unmaintained.

Marking this as a documentation issue so someone could fix the comment and grammar.md.

[alexeyzab]

Hi there!

I'd like to fix this. I'll remove the without trailing '+' part from the comment, but I am not sure which part to edit in the grammar.md. I am assuming it has to be somewhere here, the bound-list section probably?

[petrochenkov]

@alexeyzab
Placing the bounds grammar into the closure grammar seems strange (https://github.com/rust-lang/rust/blob/master/src/doc/grammar.md#closure-types is also very outdated), I'd create a new separate paragraph for it.
The current grammar for bounds can be found here.
There are also two places mentioning "without trailing '+'", the second one needs to be fixed as well.

[alexeyzab]

@petrochenkov Good point, my bad. Thanks for pointing that out!

[alexeyzab]

Adjusted the comment and made a new paragraph for the current grammar. Let me know if this is okay.