M5-0-12: Incorrect alerts on assignments of valid numerical values

[rvermeulen]

Affected rules

• cpp/autosar/signed-char-and-unsigned-char-type-shall-only-be-used-for-the-storage-and-use-of-numeric-values

Description

The implementation incorrectly implements the identification of numeric values.
Characters will have type char while numeric values will be promoted to int or unsigned int.
However, in the case of templates, the type of the numeric value will be the fully converted expressions type. That is, unsigned char in the example below.

Example

The following is compliant per example in the standard, however is still seen as a contravention.

template <typename T, T value>
class C1 {
  public:
    C1() : m_value(value) {}
  private:
    T m_value;
};

void fp_test() {
  C1<std::uint8_t, 10> l1;  // COMPLIANT[FALSE_POSITIVE]
  C1<std::uint8_t, 10U> l2; // COMPLIANT[FALSE_POSITIVE]
}

[lcartey]

This query needs to be adjusted to report cases where a PlainCharType type is implicitly converted on assignment to a signed or unsigned char - note, it currently reports when a CharType is converted, which is incorrect because CharType includes the signed/unsigned types. e.g.:

  aexp.getExplicitlyConverted().getUnspecifiedType() instanceof PlainCharType

Note: this same confusion was made in M5-0-11, and will need to be fixed there as well.

If the char is explicitly converted, that is acceptable - the query needs to be updated to handle this case as well.

Finally, for results that only appear in instantiated templates we should consider reporting them separately, as they may only exists for a specific instantiation.