Add new lint to detect dangling pointer return from closure

[PitiBouchon]

• Finish some TODO
• The lint name as_ptr_in_map is not good
• Added passing UI tests (including committed .stderr file)
• cargo test passes locally
• Executed cargo dev update_lints
• Added lint documentation
• Run cargo dev fmt

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The goal of this MR is to add a lint to detect dangling pointer from closure that can easily get undetected people think the closure should have took a reference instead of a value (see examples)

changelog: [as_ptr_in_map]: add a new lint to detect dangling pointer returned from closure

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[PitiBouchon]

The lint is working using two checks for a closure :

• return a raw pointer
• create a raw pointer from an owned parameter

if those two check are valid, the closure is potentially create a dangling pointer and should attract attention

[briansmith]

This seems very similar to dangling_pointers_from_temporaries. Importantly, not only owned values would result in dangling pointers; borrowed values would result in dangling pointers too, if they are references to temporaries. See rust-lang/rust#133263 (comment) for some of the difficulties with the existing warning's implementation.

[PitiBouchon]

This seems very similar to dangling_pointers_from_temporaries. Importantly, not only owned values would result in dangling pointers; borrowed values would result in dangling pointers too, if they are references to temporaries. See rust-lang/rust#133263 (comment) for some of the difficulties with the existing warning's implementation.

What I want to detect is things like :

let v_opt = Some(vec![0]);
let v_ptr = v_opt.map(|v| v.as_ptr());

where it is easy to forget a .as_ref() for example.

I didn't checked rustc lints (only clippy), however the dangling_pointers_from_temporaries lint doesn't seem to detect this (but maybe should in the future if the comment mentioned is resolved).

Also, I don't know how to detect temporaries 🤷

[briansmith]

I didn't checked rustc lints (only clippy), however the dangling_pointers_from_temporaries lint doesn't seem to detect this (but maybe should in the future if the comment mentioned is resolved).

I think that's rust-lang/rust#139249