Cannot move from a borrowed value

Meaning

Ordinary move-only parameters are borrowed. A function cannot drop them or transfer them into another owner.

The caller remains responsible for a default-borrowed value after the call. Allowing the callee to consume it would violate that signature contract.

Why it happens

A helper may have evolved from observation to storage/destruction without changing its parameter mode. Container insertion also needs ownership, so pushing an ordinary borrowed struct/string/list triggers the same class of error.

Invalid code

struct Item { value: Int }
fn consume(item: Item) { drop(item) }
fn main() -> Int {
    consume(Item { value: 1 })
    return 0
}

Correct code

struct Item { value: Int }
fn consume(sink item: Item) { drop(item) }
fn main() -> Int {
    consume(Item { value: 1 })
    return 0
}

Common fixes

Add sink when consumption is the function's contract, or stop consuming and keep the ordinary borrowed parameter.

Use inout instead when the callee needs caller-visible mutation but not ownership. Do not add sink solely to silence the diagnostic: doing so invalidates the caller's binding and is a public API change.