Clippy lint · Nursery · checked with Clippy 0.1.99

clippy::derive_partial_eq_without_eq: Checks for types that derive PartialEq and could implement Eq

What it meansChecks for types that derive PartialEq and could implement Eq. It is in the nursery group and off by default.

Does it matter?

If a type T derives PartialEq and all of its members implement Eq, then T can always implement Eq. Implementing Eq allows T to be used in APIs that require Eq types. It also allows structs containing T to derive Eq themselves.

New lints still being finished. Off by default and may have false positives.

How to fix it

Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

#[derive(PartialEq)]
struct Foo {
    i_am_eq: i32,
    i_am_eq_too: Vec<String>,
}

Write this instead

#[derive(PartialEq, Eq)]
struct Foo {
    i_am_eq: i32,
    i_am_eq_too: Vec<String>,
}

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
derive_partial_eq_without_eq = "warn"

In code

#![warn(clippy::derive_partial_eq_without_eq)]

One run

cargo clippy -- -W clippy::derive-partial-eq-without-eq

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.

Nurserygroup

allowdefault level

yesfixed by cargo clippy --fix

1.63.0added in Rust

Clippy's own documentation

What it does

Checks for types that derive PartialEq and could implement Eq.

Why is this bad?

If a type T derives PartialEq and all of its members implement Eq, then T can always implement Eq. Implementing Eq allows T to be used in APIs that require Eq types. It also allows structs containing T to derive Eq themselves.

Example

#[derive(PartialEq)]
struct Foo {
    i_am_eq: i32,
    i_am_eq_too: Vec<String>,
}

Use instead:

#[derive(PartialEq, Eq)]
struct Foo {
    i_am_eq: i32,
    i_am_eq_too: Vec<String>,
}

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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