False positive with rule cpp:S6012

Hello and good morning,

so it seems that the detection for rule cpp:S6012 (“Redundant class template arguments should not be used”) does not work correctly. I’ll attach a code snippet below:

#include <cstddef>
#include <cstdlib>

template <typename T>
class MyClass

    MyClass(size_t size, const T& value = T{}) :


    size_t _size;
    T _value;

int main()
    MyClass obj1(10);      // does not compile (obviously)
    MyClass<int> obj2(10); // "violates" rule cpp:S6012

    return EXIT_SUCCESS;

When creating obj1, compilation fails, since the template argument cannot be deduced - an explicit class template argument is required. However, if you do so (obj2), both Sonarlint in VS Code and the full analysis mark it as a violation of rule cpp:S6012. (I guess the issue is with the defaulted argument in the constructor - after all, if I gave another argument when creating the objects, it would work without the explicit template argument.)

Rule cpp:6012 states “This rule raises an issue when explicit class template arguments that can be automatically deduced is specified.”. As far as I can see, it cannot be automatically deduced for obj2 so the issues should not be raised.

Feel free to correct me if I’m missing something but that just seems like a bug in the analysis.

Hello @moth, and welcome to our community!

Thanks for reporting this false positive. I agree with your analysis and created [CPP-4909] - Jira to track our progress toward fixing this issue.


Thank you!

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