[WIP] Trigger absurd_extreme_comparisons if Duration is less than zero

[alex-semenyuk]

Close #14524

changelog: [absurd_extreme_comparisons]: triggers if Duration is less than 0

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[samueltardieu]

In its current state, the lint would:

• fail with a false positive in some situations where a non-zero Duration is returned by a function (see detailed comment)
• fail with a false negative with other const initializers, such as Duration::new(0, 0), Duration::from_secs_f32(0), and Duration::from_secs_f64(0).

This can be fixed in several ways:

• A list of methods to match against can be used, with a special case for Duration::new(0, 0) (easier)
• Or the const evaluator could be enriched to include a Duration variant (more complex, probably not worth it)

[samueltardieu]

You can use something like:

Suggested change

	if let ExprKind::Call(_, args) = &expr.kind
	&& args.len() == 1
	if let ExprKind::Call(_, [arg]) = &expr.kind

[samueltardieu]

This is not robust enough, as this will match any function whose argument is 0 and returns a Duration, including a function such as:

    fn one_second_plus(n: u64) -> Duration {
        Duration::from_secs(n+1)
    }

which does not return a zero duration.

[samueltardieu]

I know the PR is still in draft mode, but I'll comment right now since function name matching has changed recently: we don't use &str anymore to compare a function name against an expected value when we can use interned symbols from clippy_utils::sym, as comparisons are much faster. If sym::from_secs (for example) is not available already, you can add it to clippy_utils::sym and it will be made available.

But here, since you want to look up entities, there is also another way to go: you can add the path to the associated functions you need to identify, e.g., core::time::Duration::from_secs, in clippy_utils::paths.rs, as:

pub static DURATION_FROM_SECS: PathLookup = value_path!(core::time::Duration::from_secs);

You will then be able to use DURATION_FROM_SECS.matches(def_id) where def_id is the DefId of the function you want to check, and it will tell you whether this is indeed Duration::from_secs(). You shouldn't need to match the type and the associated function separately.

Hope it helps.