`deprecated` attribute should give error with bad arguments

[lucasly-ba]

code:

#[deprecated(a,a)]
pub fn a(){}

expected:

error[E0541]: unknown meta item 'a'
 --> a.rs:5:14
  |
5 | #[deprecated(a,a)]
  |              ^ expected one of `since`, `note`

error: aborting due to previous error

code:

#[deprecated("a")]
pub fn a(){}

expected:

error[E0565]: item in `deprecated` must be a key/value pair
 --> a.rs:5:14
  |
5 | #[deprecated("a")]
  |              ^^^

error: aborting due to previous error

code:

#[deprecated(since=a, note=a)]
pub fn A(){}

Expected:

error: expected unsuffixed literal or identifier, found `a`
 --> a.rs:5:20
  |
5 | #[deprecated(since=a, note=a)]
  |                    ^

error: aborting due to previous error

[sneaky-potato]

Hi can I take this up?