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Python: Port UnusedExceptionObject.ql #21601

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Python: Port UnusedExceptionObject.ql #21601

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46 changes: 42 additions & 4 deletions python/ql/src/Statements/UnusedExceptionObject.ql
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Original file line number Diff line number Diff line change
Expand Up @@ -12,11 +12,49 @@
*/

import python
private import LegacyPointsTo
private import semmle.python.dataflow.new.internal.DataFlowDispatch
private import semmle.python.dataflow.new.internal.Builtins
private import semmle.python.ApiGraphs

from Call call, ClassValue ex
/**
* Holds if `cls` is a user-defined exception class, i.e. it transitively
* extends one of the builtin exception base classes.
*/
predicate isUserDefinedExceptionClass(Class cls) {
cls.getABase() =
API::builtin(["BaseException", "Exception"]).getAValueReachableFromSource().asExpr()
or
isUserDefinedExceptionClass(getADirectSuperclass(cls))
}

/**
* Gets the name of a builtin exception class.
*/
string getBuiltinExceptionName() {
result = Builtins::getBuiltinName() and
(
result.matches("%Error") or
result.matches("%Exception") or
result.matches("%Warning") or
result =
["GeneratorExit", "KeyboardInterrupt", "StopIteration", "StopAsyncIteration", "SystemExit"]
)
}

/**
* Holds if `call` is an instantiation of an exception class.
*/
predicate isExceptionInstantiation(Call call) {
exists(Class cls |
classTracker(cls).asExpr() = call.getFunc() and
isUserDefinedExceptionClass(cls)
)
or
call.getFunc() = API::builtin(getBuiltinExceptionName()).getAValueReachableFromSource().asExpr()
}

from Call call
where
call.getFunc().(ExprWithPointsTo).pointsTo(ex) and
ex.getASuperType() = ClassValue::exception() and
isExceptionInstantiation(call) and
exists(ExprStmt s | s.getValue() = call)
select call, "Instantiating an exception, but not raising it, has no effect."
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