An non plain assignment operation is one where the lhs is evaluated before the right hand side expression is. For example a += expr is the equivalent of a = a + expr. While the Jessie rules disallow a + await expr we mistakenly allowed a += await expr.
An non plain assignment operation is one where the lhs is evaluated before the right hand side expression is. For example
a += expris the equivalent ofa = a + expr. While the Jessie rules disallowa + await exprwe mistakenly alloweda += await expr.Fixes #89