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Refactor ReExposedInstance logic into one place

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This commit is contained in:
Owen Mansel-Chan
2026-06-17 13:10:47 +01:00
parent 415857cacb
commit ea7510bf72
3 changed files with 57 additions and 36 deletions
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25
python/ql/src/Statements/ShouldUseWithStatement.ql
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@@ -15,6 +15,7 @@
import python
private import semmle.python.dataflow.new.DataFlow
private import semmle.python.dataflow.new.internal.DataFlowDispatch
private import semmle.python.dataflow.new.internal.ReExposedInstance
predicate calls_close(Call c) { exists(Attribute a | c.getFunc() = a and a.getName() = "close") }
@@ -24,26 +25,10 @@ predicate only_stmt_in_finally(Try t, Call c) {
)
}
/**
* Holds if `read` is an attribute read that re-exposes an instance of `cls` held in an
* instance attribute, for example `BufferedRWPair.reader`.
*
* Instance-attribute type tracking can launder such an instance out of a field. The object
* is owned by the enclosing instance, so its lifetime spans that instance and cannot be
* expressed with a `with` statement; closing it in a `finally` block is therefore not a
* candidate for refactoring.
*/
private predicate launderedAttrRead(Class cls, DataFlow::AttrRead read) {
read = classInstanceTracker(cls)
}
/** Holds if `node` is tracked to be an instance of some class. */
private predicate classInstanceNode(DataFlow::Node node) { node = classInstanceTracker(_) }
/** Type tracking forward from an attribute read that re-exposes an instance held in a field. */
private DataFlow::TypeTrackingNode launderedInstance(Class cls, DataFlow::TypeTracker t) {
t.start() and
launderedAttrRead(cls, result)
or
exists(DataFlow::TypeTracker t2 | result = launderedInstance(cls, t2).track(t2, t))
}
private module ClassReExposed = ReExposedInstance<classInstanceNode/1>;
from Call close, Try t, Class cls, DataFlow::Node closeTarget
where
@@ -54,7 +39,7 @@ where
// Don't report closing a resource that is held in an instance attribute (e.g. `self.reader`).
// Such flow is introduced by instance-attribute type tracking; the object's lifetime is tied
// to the enclosing instance and cannot be expressed with a `with` statement.
not launderedInstance(cls, DataFlow::TypeTracker::end()).flowsTo(closeTarget) and
not ClassReExposed::isReExposed(closeTarget) and
DuckTyping::isContextManager(cls)
select close,
"Instance of context-manager class $@ is closed in a finally block. Consider using 'with' statement.",