needless-pass-by-value

Disallow passing parameters by value when they are never consumed or mutated

Taking ownership of a move-only parameter prevents callers from retaining it when the body only reads the value.
Instead, you SHOULD accept a readonly borrow when the function neither mutates nor consumes the parameter.
Keep ownership when transferring the value is part of the callable's behavior.

- Category: performance
- Level: warning
- Fix: none
- Scope: module

Reported

struct Packet {
    code: int32;
}

function packetCode(packet: Packet): int32 {
    return packet.code;
}
Accepted

struct Packet {
    code: int32;
}

function packetCode(packet: &readonly Packet): int32 {
    return packet.code;
}
Prior art

- Clippy · needlesspassbyvalue

language/linter/src/rules/performance/needlesspassbyvalue.rs:9