C++: Ignore destructor calls on temporaries in IR translation classes

[MathiasVP]

Consider this snippet (which I also added as a test in this PR):

struct A { int a[2]; ~A(); };

void f(bool b) {
  const int &t = b ? A().a[0] : A().a[1];
  return;
}

Currently, the extractor incorrectly places each temporary's destructor call inside the conditional branches. However, an upcoming extractor fix will move those destructor calls to the return statement. This revealed a bug in the IR's placement of destructors.

IR construction only generates destructors for non-conditional destruction. We do this by filtering out those expressions here. However, we forgot to filter out the calls to conditional destructors inside the translation classes. For example here where we just return any destructor without checking if that destructor is conditional.

Unfortunately, I was unable to craft a testcase that fails on the current version of the extractor. So it's a bit hard to judge the impact of this PR. I did, however, check that this fixes the issue when running on a database extracted with CodeQL running the fixed version of the extractor.

[Copilot]

Note

Copilot was unable to run its full agentic suite in this review.

Copilot review overview

Review effort: Lite
Findings: 1 · 1

Open (2)

• The destructor is declared but not defined. Even if this test suite usually compiles without… · New
• The filtered rank[...] logic for implicit destructor calls is now duplicated in both… · New

What changed in this PR

Updates the C++ IR translation logic to ignore implicit destructor calls for temporaries created within conditional evaluation contexts, and adds a regression test covering conditional-operator temporaries with non-trivial destructors.

Changes:

• Add temp_test13 demonstrating temporaries with destructors inside a ternary that returns an lvalue subobject.
• Filter implicit destructor calls in IR translation to exclude “conditional temporary destructor calls”.
• Update IR/AST expected outputs to match the new filtering behavior.

File	Description
cpp/​ql/​test/​library-tests/​ir/​ir/​destructors_for_temps.cpp	Adds a new test case and a struct with array + destructor to exercise conditional temporary destructor handling.
cpp/​ql/​test/​library-tests/​ir/​ir/​raw_ir.expected	Updates the raw IR snapshot to include temp_test13 and its new control-flow/aliasing behavior.
cpp/​ql/​test/​library-tests/​ir/​ir/​aliased_ir.expected	Updates aliased IR snapshot consistent with the new implicit-dtor filtering.
cpp/​ql/​test/​library-tests/​ir/​ir/​PrintAST.expected	Updates AST snapshot showing the implicit destructor calls attached to the conditional expression.
cpp/​ql/​lib/​semmle/​code/​cpp/​ir/​implementation/​raw/​internal/​TranslatedStmt.qll	Introduces filtered indexing for implicit destructor calls and uses it across statement child traversal.
cpp/​ql/​lib/​semmle/​code/​cpp/​ir/​implementation/​raw/​internal/​TranslatedExpr.qll	Applies the same filtered indexing for expression-attached implicit destructor calls.
cpp/​ql/​lib/​semmle/​code/​cpp/​ir/​implementation/​raw/​internal/​TranslatedElement.qll	Changes visibility of isConditionalTemporaryDestructorCall to support reuse in other internal modules.

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[jketema]

LGTM