RFC: Simplify attribute syntax

[glaebhoerl]

Instead of

#[attr1, attr2(foo)]

write

#attr1 #attr2(foo)

in other words, instead of a list of attributes delimited by [], # would introduce a single attribute, and multiple attributes would be written as multiple single attributes.

This is less busy visually, especially when there's only one attribute, which is common. In terms of character count it requires 1 character for a single attribute (vs. 3 with the current syntax), and 2 additional characters for each additional attribute (same as the current syntax).

And it looks like hashtags, which is cute and not a bad intuition.

I don't know why the syntax is the way it is right now: historically, I think it's probably because macros were originally #foo() rather than foo!()? But I don't see any other potential for conflict in today's syntax. (The only other place the # character is even used, as far as I know, is raw strings.)

[alexcrichton]

Closing as a dupe of #2569. There has been a very large amount of discussion in that other bug, and I believe the settled-upon syntax was:

#^ inner(attribute)

#outer(attribute)
fn main() {}

And we would no longer attributes at the outer layer of the form name = "value"

[liigo]

2013/12/26 Gábor Lehel notifications@github.com

Instead of

#[attr1, attr2(foo)]

write

#attr1 #attr2(foo)

+1, this is better and simpler

[glaebhoerl]

Oh, for some reason I hadn't remembered #2569 also talked about dropping the brackets. Sorry!