False positive in bugprone-string-constructor

[JVApen]

#include <string>

void f(std::string str)
{
      const char *ptr = str.c_str();
      std::string copy(ptr, 0, str.size()/2);
}

On Compiler Explorer: https://compiler-explorer.com/z/KEEPh3Kz1

The result:

[<source>:7:19: warning: constructor creating an empty string [bugprone-string-constructor]]
   7 |       std::string copy(ptr, 0, str.size()/2);
      |                   ^
1 warning generated.

In this example, the following constructor of std::string should be called:

template< class StringViewLike >
basic_string( const StringViewLike& t,
              size_type pos, size_type count,
              const Allocator& alloc = Allocator() );

Since we provide a valid pointer and a valid non-0 count, the string isn't empty by default.
As such, the warning should not be given.

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: None (JVApen)

```` #include <string>

void f(std::string str)
{
// Find the substring "FAMILY:" (copied from old code so still using C-style Char pointers)
const char *ptr = str.c_str();
std::string copy(ptr, 0, str.size()/2);
}

On Compiler Explorer: https://compiler-explorer.com/z/1o86onvGG

The result:

[<source>:7:19: warning: constructor creating an empty string [bugprone-string-constructor]]
7 | std::string copy(ptr, 0, str.size()/2);
| ^
1 warning generated.

In this example, the following constructor of std::string should be called:

template< class StringViewLike >
basic_string( const StringViewLike& t,
size_type pos, size_type count,
const Allocator& alloc = Allocator() );

Since we provide a valid pointer and a valid non-0 count, the string isn't empty by default.
As such, the warning should not be given.

</details>

[chrchr-github]

Reduced:

void f(const char *ptr, size_t n) {
      std::string s(ptr, 0, n);
}

False negatives:

void f(const char *ptr) {
      std::string s(ptr, size_t(0));
}

void f(const char *ptr) {
      std::string s(ptr, 1, 0);
}