[SMTChecker] Fix comparison of CHCVerificationTarget for proper std::set ordering

[radik878]

What was changed

• Moved comparison logic from SafeTargetsCompare struct to CHCVerificationTarget::operator<
• Removed the SafeTargetsCompare struct completely
• Fixed a bug where == was used instead of < in the comparison operator
• Updated std::set<CHCVerificationTarget, SafeTargetsCompare> to use default std::set<CHCVerificationTarget>

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[blishko]

LGMT!

Thanks for finding this out!
I am fine with merging this, but I will look into it further, because CHCVerificationTarget also provides operator<, which, however, works completely differently, which is weird.
I don't think we need both.

[blishko]

It looks like the operator< on CHCVerificationTarget is not really used now.
I think we should just replace the implementation of the operator with the fixed implementation of SafeTargetsCompare and then delete SafeTargetsCompare.

[radik878]

It looks like the operator< on CHCVerificationTarget is not really used now. I think we should just replace the implementation of the operator with the fixed implementation of SafeTargetsCompare and then delete SafeTargetsCompare.

Did i make changes correctly?

[cameel]

Just two general notes:

• The current state of the PR seems to be actually changing the behavior of the operator slightly, but no tests needed to be updated. That's always suspicious. Either we're missing test coverage or the code is not actually running.
• Please remember to update the PR/commit description if you change what the PR is about. Currently it still says it's doing what you originally tried to do, which is very misleading.

[blishko]

Yes, this is what I meant.

I've just noticed that there was an extra space, can you fix that as well?
Also, can you rebase your branch? I believe that should fix the external tests in CI.

[blishko]

• The current state of the PR seems to be actually changing the behavior of the operator slightly, but no tests needed to be updated. That's always suspicious. Either we're missing test coverage or the code is not actually running.

My understanding is that this only affects the order of verification targets proved safe.
If I remember correctly, we usually just count them and report the count to the user.
I'll have to think about a way to design a test for this.

• Please remember to update the PR/commit description if you change what the PR is about. Currently it still says it's doing what you originally tried to do, which is very misleading.

I agree, please update the description.

[blishko]

@cameel, I have checked the codebase and it turns out that the problematic piece of code (one fixed in this PR) is indeed never reached at the moment.

In current codebase the comparison is only used in std::map<ASTNode const*, std::set<CHCVerificationTarget>, smt::EncodingContext::IdCompare> m_safeTargets, in the value, which is a set of CHCVerificationTarget, where the verification targets are sorted.
However, we only add two targets to the same set if they are associated with the same ASTNode, which is the key in the m_safeTargets map.
So we only have compare two targets if they have the same errorNode, which is exactly the if-condition of the comparison.

Thus currently, the bug was never triggered, but it was indeed a hidden bug in the implementation.

My conclusion is that other than a unit test, we are not able to test the changed place in the code, and we don't have unit tests, right?
So, I would merge this PR, after it is rebased and description updated, as is.

[radik878]

@cameel, I have checked the codebase and it turns out that the problematic piece of code (one fixed in this PR) is indeed never reached at the moment.

In current codebase the comparison is only used in std::map<ASTNode const*, std::set<CHCVerificationTarget>, smt::EncodingContext::IdCompare> m_safeTargets, in the value, which is a set of CHCVerificationTarget, where the verification targets are sorted. However, we only add two targets to the same set if they are associated with the same ASTNode, which is the key in the m_safeTargets map. So we only have compare two targets if they have the same errorNode, which is exactly the if-condition of the comparison.

Thus currently, the bug was never triggered, but it was indeed a hidden bug in the implementation.

My conclusion is that other than a unit test, we are not able to test the changed place in the code, and we don't have unit tests, right? So, I would merge this PR, after it is rebased and description updated, as is.

updated description

[blishko]

Thanks!