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Python: Fix bad join order in TypeTracker::callStep #4679

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Python: Fix bad join order in TypeTracker::callStep #4679

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18 changes: 16 additions & 2 deletions python/ql/src/semmle/python/dataflow/new/TypeTracker.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -87,11 +87,25 @@ private predicate typePreservingStep(Node nodeFrom, Node nodeTo) {
nodeFrom = nodeTo.(PostUpdateNode).getPreUpdateNode()
}

/**
* Helper predicate to avoid bad join order experienced in `callStep`.
*
* This happened when `isParameterOf` was joined _before_ `getCallable`.
*/
pragma[nomagic]
private DataFlowCallable callStepHelper(ArgumentNode nodeFrom, int i) {
exists(DataFlowCall call |
nodeFrom.argumentOf(call, i) and
result = call.getCallable()
)
}

/** Holds if `nodeFrom` steps to `nodeTo` by being passed as a parameter in a call. */
predicate callStep(ArgumentNode nodeFrom, ParameterNode nodeTo) {
// TODO: Support special methods?
exists(DataFlowCall call, int i |
nodeFrom.argumentOf(call, i) and nodeTo.isParameterOf(call.getCallable(), i)
exists(DataFlowCallable callable, int i |
callable = callStepHelper(nodeFrom, i) and
nodeTo.isParameterOf(callable, i)
)
}

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