`A0-1-1`: `auto` local variables in uninstantiated templates are reported as unused

[lcartey]

Affected rules

• A0-1-1

Description

Where an auto variable is declared in a template function or class, the copy of the variable in the uninstantiated template may be considered "unused", even though it is considered used in at least one instantiation.

Example

#include <vector>
template <typename T> void test_range_based_for_loop_template() {
  std::vector<A> values_;
  for (auto &elem : values_) { // COMPLIANT - should not report either elem or
                               //             the compiler generated (__range)
                               //             variable in the uninstantiated
                               //             template
    elem;
  }
}

// Instantiate the template
void test_template() { test_range_based_for_loop_template<A>(); }

[lcartey]

Updated with a refinement of our understanding of the problem.

[lcartey]

I believe I've determined the cause of this issue - I've updated the issue body to reflect this.