`// PANIC` comment on panic-able calls

[blyxyas]

What it does

Reports on functions marked as panic-able (for example, .expect()) in the config file or with a special #[clippy::may_panic].

Advantage

• Ensures that specially critical code is handled with the requirement that it won't panic
• Allows for more flexibility than unwrap_used or disallowed_methods

Drawbacks

No response

Example

#[clippy::may_panic]
fn dangerous(v: Vec<usize>) -> usize {
    v[1]
}

fn foo()  {
    let v = vec![];
    let _ = dangerous(v);
}

Comparison with existing lints

Unlike unwrap_used, this allows for any function marked such as that.
Compared disallowed_methods, this allows for any function call and gives a specific reason.
Unlike indexing_slicing, this works for any function marked as clippy::may_panic
Unlike unreachable/unimplemented, this works for any functions marked with the attribute.

Additional Context

This was requested by the Rust-for-Linux project, giving it priority. I will mentor anyone trying to implement it.

[hcbarker]

@rustbot claim

I'd love to work on this, and would certainly appreciate some mentorship :)

[blyxyas]

Hi @hcbarker!
Thanks for taking the time to contribute to Clippy. I'll guide you through this process (and obviously respond any question that you might have)

First of all, some useful resources:

• Rust's Zulip is used for instant messaging with anyone on the team, you can find me for more direct messaging.
• Rust Clippy book
• Rustdoc for rustc_hir (an internal module, not useful to you right now)
• The rustc dev guide, it has some information that the Clippy book doesn't have because it's more related at compiler internals, more than Clippy internals

---

I suggest that you start by reading the Clippy book, it teaches you how to add a lint. For examples on how current lints are written, I'd say that this specific lint could be similar to how undocumented_unsafe_blocks works.

Note that, in the end, a Clippy lint is just a struct that implements a special trait that goes token-by-token, expr-by-expr, item-by-item, calling a set of functions to check that item and emit a warn if necessary.

[blyxyas]

Once you have a pull request, write "r? blyxyas" somewhere on the body of your pull request.
Also note that I might be slow to respond on weekends, I'm under direct threat from my partner that if I review anything on weekends, she'll assassinate me hit-man style.

[hcbarker]

@blyxyas Thanks a bunch! I'll reach out on Zulip as I have questions :)