[nll] better error message when returning refs to upvars by davidtwco · Pull Request #54802 · rust-lang/rust (original) (raw)

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Here I suspect this will be a bit confusing because two closures are in play. We actually can probably tell that — if the statement is an assignment with a closure rvalue, then there is an "inner" and an "outer" closure, and maybe we can adjust the message to say something like:

creates a closure that captures x by reference; this inner closure is then returned from the outer closure, allowing x to escape the closure body

that wording doesn't feel 💯, though, and I don't know if it's easy to find the name x (we don't seem to be using it in other messages)

Maybe something like this?

creates a closure that contains a reference to a captured variable; this inner closure then escapes the closure body