Indexing operations are not accurate on whether they panic

[estebank]

rustc doesn't mark the internal APIs that it uses to determine the appropriate trait used by an indexing operation as public. For now, the dont_panic lint always treats indexing as a potentially panicking operation as a stop-gap.

[Erk-]

This does not seem to work with indexing that does not use usize as the index, for example it does not seem to catch the following panic:

fn main() {
    let mut map = std::collections::HashMap::new();
    map.insert("foo", "bar");
    map["baz"];
}