Lint for soft-deprecated `{integer}::max_value` and `min_value`

[tesuji]

What it does

Currently, Rust have three way to getting min/max of an integers:

1. module constants: std::i32::MAX
2. type constants: i32::MAX
3. const methods: i32::max_value()

(3) is soft-deprecated and replaced by 2) when possible.

T-libs doesn't want to deprecate 1) and 3) now until next Rust edition,
but we have no tools to enforce style for 2),
it is great to have such a lint in Clippy.

Categories (optional)

• Kind: style

Drawbacks

None.

[kangalio]

I'll try to do this

[kangalio]

I'm a bit stuck because I can't properly figure out a way to detect "indirect" min_value()/max_value() calls.

impl Foo {
    type Int = i32;
    fn min_value() -> Int {
        Self::Int::min_value() // lint
    }
}
Foo::min_value(); // shouldn't lint!
Foo::Int::min_value(); // lint

type Int = i32;
let _ = Int::min_value(); // lint

I'm helpless with the rustc internals and its documentation is hardly helping.

[flip1995]

You have to compare the path of the functions. You can search the Clippy codebase for match_qpath to find out how it is used.

[kangalio]

As far as I can tell, match_qpath is for matching a path 1:1. However, I need a way to "resolve" paths to the actual function and call against that. I don't see any way of using match_qpath that would catch all three cases I've outlined above

[flip1995]

Ah I see. This may work with

rust-clippy/clippy_lints/src/utils/mod.rs

Line 1358 in 2e0f8b6

pub fn fn_def_id(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<DefId> {

which you can then compare to the def_id of the min_value function. This can be done with

rust-clippy/clippy_lints/src/utils/mod.rs

Line 1184 in 2e0f8b6

pub fn match_def_path<'tcx>(cx: &LateContext<'tcx>, did: DefId, syms: &[&str]) -> bool {

[phansch]

There has been some progress on the Rust side of things (tracking issue). Rust has recently added support for 'soft-deprecation' of items: rust-lang/rust#79877. The next step will be to soft-deprecate the old items in std directly.

Considering that, I don't think it makes sense to implement this in Clippy anymore and I'm going to go ahead and close this issue.

Thanks everyone for your interest in working on this lint 💙