Suggest using `==` instead of `matches!`

[emilk]

What it does

Looks for unnecessary uses of matches! that can be replaced with == or !=

Advantage

Using matches! can produce unnecessarily complex code. When negated, you also get the "double-bang" confusion of !matches!(…), where tje twp ! means different things.

Drawbacks

No response

Example

if !matches!(value, Enum::Variant) { … 

Could be written as:

if value != Enum::Variant { … 

[lukaslueg]

FWIW: Notice that value != Enum::Variant requires Enum: PartialEq, while matches! does not; this also means Enum<T: PartialEq>, even if Enum::Variant does not carry a T. We have a warn-by-default lint wrt value == None in place so people don't fall into this specific pattern. IMHO its not advisable to teach people to do by-value comparison if structural comparison is what they need.

[emilk]

Yes, we should of course only suggest using == or != for types that implement PartialEq

[NullSpaceBoy]

@rustbot claim

[nik-rev]

I don't think this lint should be warn-by-default, this should probably be in the pedantic category.

See discussion on this PR, which tried to replace some matches! with ==, but it was somewhat controversial: rust-lang/rust#149933. I agree with the points mentioned there

[GuillaumeGomez]

Opened #17018.