attributes: force instrumented function to be FnOnce
#2897
Closed
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Closes #2857
Motivation
Functions which are
Fn
orFnMut
fail to compile when they are instrumented with#[instrument(ret)]
Solution
I've added a non-copy zst (
[&mut (), 0]
) to the generated code that is moved inside the function so that it is forced to be no more thanFnOnce
.