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/**

* @name Explicit returns mixed with implicit (fall through) returns

* @description Mixing implicit and explicit returns indicates a likely error as implicit returns always return `None`.

* @kind problem

* @tags quality

* reliability

* correctness

* @problem.severity recommendation

* @sub-severity high

* @precision high

* @id py/mixed-returns

import python

private import LegacyPointsTo

predicate explicitly_returns_non_none(Function func) {

exists(Return return |

return.getScope() = func and

exists(Expr val | val = return.getValue() | not val instanceof None)

)

}

predicate has_implicit_return(Function func) {

exists(ControlFlowNodeWithPointsTo fallthru |

fallthru = func.getFallthroughNode() and not fallthru.unlikelyReachable()

)

exists(Return return | return.getScope() = func and not exists(return.getValue()))

}

from Function func

where explicitly_returns_non_none(func) and has_implicit_return(func)

select func,

"Mixing implicit and explicit returns may indicate an error, as implicit returns always return None."