Rules for matching against variable unclear.

[XAMPPRocky]

When you have a match statement against a variable the behaviour is unexpected.

I tried this code:

fn main() {
    let x = 'x';
    let c = 'c';
    match c {
        x => println!("Bug? {} {}", x, c),
    }

    println!("x: {}", x)
}

I expected to to see this happen:

Either get an error telling me that placing a variable won't do what I think it will do. Or allow this to happen, and allow for specific cases, as currently adding any extra arms returns a unreachable pattern error.

Instead this happened:

This compiles with no errors, or warning, and prints out:

Bug? c c
x: x

Meta

rustc --version --verbose

rustc 1.3.0 (9a92aaf19 2015-09-15)
binary: rustc
commit-hash: 9a92aaf19a64603b02b4130fe52958cc12488900
commit-date: 2015-09-15
host: x86_64-apple-darwin
release: 1.3.0

[bluss]

You can match against patterns that are composed of: Literals, ranges, Struct constructors, Enum variant constructors and const constants.

If you put in an identifier like this it's just a new binding (a catch-all). Rust generally allows variable shadowing without warning (let x = 1; let x = x + 1 is ok), so this is consistent with that at least.

[bluss]

Relevant doc section is Patterns. I think it could be clarified around this issue.

[steveklabnik]

tagging with docs to see if i can make this somehow more prominent, but I'm not sure.