Rust-clippy: panic_params: Don't lint non-format-string `{}`

[alexd2580]

± cargo --version
    cargo 0.19.0-nightly (03efb7fc8 2017-04-23)
± rustc --version
    rustc 1.18.0-nightly (94e884b63 2017-04-27)
± cargo clippy --version
    0.0.128

The following code:

assert!({ true });

triggers the following lint:

warning: you probably are missing some parameter in your format string
 --> src/lib.rs:2:5
  |
2 |     assert!({ true });
  |     ^^^^^^^^^^^^^^^^^^
  |

This is a false positive, because the curly braces are rust code identifiers, not format string tokens.
I use this syntax with the braces to put complex expressions inside the assert!s which should not be part of the regular code.

[oli-obk]

We should have an A-musing label

[mcarton]

@oli-obk You can do that by yourself in Issues → Labels (on the right of the search bar).
(took me a while to find that)

[oli-obk]

xD I know, but I wasn't sure about the resonance I'd get if I start throwing around useless labels

[behnam]

This is now being triggered in UNIC for this assertion: https://github.com/behnam/rust-unic/blob/master/unic/ucd/age/tests/age_tests.rs#L35-L42

[llogiq]

I think the problem is that we just get the source for the contained token tree and look there for brackets.

[oli-obk]

should be easy enough to check whether the token tree starts and ends with quotes