C++: Fix queries after shared guards

[MathiasVP]

Description

github/codeql#20485 switches C/C++ away from its own guards library and over to the shared guards library (which is currently used by Java, and soon by C#). One of the changes is that a GuardCondition is now an Element instead of always being an Expr. So a couple of the coding standard queries needs an additional cast.

Change request type

• Release or process automation (GitHub workflows, internal scripts)
• Internal documentation
• External documentation
• Query files (.ql, .qll, .qls or unit tests)
• External scripts (analysis report or other code shipped as part of a release)

Rules with added or modified queries

• No rules added
• Queries have been added for the following rules:
  • rule number here
• Queries have been modified for the following rules:
  • rule number here

Release change checklist

A change note (development_handbook.md#change-notes) is required for any pull request which modifies:

• The structure or layout of the release artifacts.
• The evaluation performance (memory, execution time) of an existing query.
• The results of an existing query in any circumstance.

If you are only adding new rule queries, a change note is not required.

Author: Is a change note required?

• Yes
• No

🚨🚨🚨
Reviewer: Confirm that format of shared queries (not the .qll file, the
.ql file that imports it) is valid by running them within VS Code.

• Confirmed

Reviewer: Confirm that either a change note is not required or the change note is required and has been added.

• Confirmed

Query development review checklist

For PRs that add new queries or modify existing queries, the following checklist should be completed by both the author and reviewer:

Author

• Have all the relevant rule package description files been checked in?
• Have you verified that the metadata properties of each new query is set appropriately?
• Do all the unit tests contain both "COMPLIANT" and "NON_COMPLIANT" cases?
• Are the alert messages properly formatted and consistent with the style guide?
• Have you run the queries on OpenPilot and verified that the performance and results are acceptable?
  As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
• Does the query have an appropriate level of in-query comments/documentation?
• Have you considered/identified possible edge cases?
• Does the query not reinvent features in the standard library?
• Can the query be simplified further (not golfed!)

Reviewer

• Have all the relevant rule package description files been checked in?
• Have you verified that the metadata properties of each new query is set appropriately?
• Do all the unit tests contain both "COMPLIANT" and "NON_COMPLIANT" cases?
• Are the alert messages properly formatted and consistent with the style guide?
• Have you run the queries on OpenPilot and verified that the performance and results are acceptable?
  As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
• Does the query have an appropriate level of in-query comments/documentation?
• Have you considered/identified possible edge cases?
• Does the query not reinvent features in the standard library?
• Can the query be simplified further (not golfed!)

[Copilot]

Pull Request Overview

This PR fixes compatibility issues in C++ queries following the migration from a C/C++-specific guards library to a shared guards library. The key change is that GuardCondition is now an Element instead of always being an Expr, requiring explicit casts in several queries.

• Adds explicit casts to Expr when accessing children of GuardCondition objects
• Updates class inheritance to use instanceof Expr constraint for GuardCondition
• Maintains existing functionality while ensuring type safety after the guards library migration

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
FunctionErroneousReturnValueNotTested.qll	Adds explicit cast to Expr when accessing children of GuardCondition
DetectAndHandleMemoryAllocationErrors.ql	Adds explicit cast to Expr when accessing children of GuardCondition
DoNotUseAnAdditiveOperatorOnAnIterator.ql	Adds explicit casts to Expr for GuardCondition child access in multiple locations
DoNotCompareFunctionPointersToConstantValues.ql	Updates class inheritance to constrain GuardCondition to instanceof Expr

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