SmallString: Replace manual itoa implementation with std::to_chars

GCC 12 was producing a huge warning log about this, thinking we were
overflowing the buffer. I don't see how.

In function ‘std::_Require<std::__not_<std::__is_tuple_like<_Tp> >, std::is_move_constructible<_Tp>, std::is_move_assignable<_Tp> > std::swap(_Tp&, _Tp&) [with _Tp = char]’,
    inlined from ‘void std::iter_swap(_ForwardIterator1, _ForwardIterator2) [with _ForwardIterator1 = char*; _ForwardIterator2 = char*]’ at /usr/include/c++/12/bits/stl_algobase.h:182:11,
    inlined from ‘void std::__reverse(_RandomAccessIterator, _RandomAccessIterator, random_access_iterator_tag) [with _RandomAccessIterator = char*]’ at /usr/include/c++/12/bits/stl_algo.h:1107:18,
    inlined from ‘void std::reverse(_BIter, _BIter) [with _BIter = char*]’ at /usr/include/c++/12/bits/stl_algo.h:1134:21,
    inlined from ‘static std::size_t Utils::BasicSmallString<Size>::itoa(long long int, char*, uint) [with unsigned int Size = 31]’ at smallstring.h:956:21,
[... many more frames ...]
move.h:205:11: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
smallstring.h:615:14: note: at offset 46 into destination object ‘buffer’ of size 22
  615 |         char buffer[22];
      |              ^~~~~~
smallstring.h:615:14: note: at offset [14, 22] into destination object ‘buffer’ of size 22
smallstring.h:615:14: note: at offset 46 into destination object ‘buffer’ of size 22

Change-Id: Iba16e8ea451b444ab213fffd16f491e608ee713a
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/libs/utils/smallstring.h

@@ -39,6 +39,7 @@
 #endif
 
 #include <algorithm>
+#include <charconv>
 #include <cmath>
 #include <cstdlib>
 #include <climits>
@@ -603,19 +604,31 @@ public:
     static
     BasicSmallString number(int number)
     {
-        char buffer[12];
-        std::size_t size = itoa(number, buffer, 10);
-
-        return BasicSmallString(buffer, size);
+#ifdef __cpp_lib_to_chars
+        // +1 for the sign, +1 for the extra digit
+        char buffer[std::numeric_limits<int>::digits10 + 2];
+        auto result = std::to_chars(buffer, buffer + sizeof(buffer), number, 10);
+        Q_ASSERT(result.ec == std::errc{});
+        auto endOfConversionString = result.ptr;
+        return BasicSmallString(buffer, endOfConversionString);
+#else
+        return std::to_string(number);
+#endif
     }
 
     static
     BasicSmallString number(long long int number)
     {
-        char buffer[22];
-        std::size_t size = itoa(number, buffer, 10);
-
-        return BasicSmallString(buffer, size);
+#ifdef __cpp_lib_to_chars
+        // +1 for the sign, +1 for the extra digit
+        char buffer[std::numeric_limits<long long int>::digits10 + 2];
+        auto result = std::to_chars(buffer, buffer + sizeof(buffer), number, 10);
+        Q_ASSERT(result.ec == std::errc{});
+        auto endOfConversionString = result.ptr;
+        return BasicSmallString(buffer, endOfConversionString);
+#else
+        return std::to_string(number);
+#endif
     }
 
     static
@@ -913,51 +926,6 @@ private:
             m_data.allocated.data.size = size;
     }
 
-    static
-    std::size_t itoa(long long int number, char* string, uint base)
-    {
-        using llint = long long int;
-        using lluint = long long unsigned int;
-        std::size_t size = 0;
-        bool isNegative = false;
-        lluint unsignedNumber = 0;
-
-        if (number == 0)
-        {
-            string[size] = '0';
-            string[++size] = '\0';
-
-            return size;
-        }
-
-        if (number < 0 && base == 10)
-        {
-            isNegative = true;
-            if (number == std::numeric_limits<llint>::min())
-                unsignedNumber = lluint(std::numeric_limits<llint>::max()) + 1;
-            else
-                unsignedNumber = lluint(-number);
-        } else {
-            unsignedNumber = lluint(number);
-        }
-
-        while (unsignedNumber != 0)
-        {
-            int remainder = int(unsignedNumber % base);
-            string[size++] = (remainder > 9) ? char((remainder - 10) + 'a') : char(remainder + '0');
-            unsignedNumber /= base;
-        }
-
-        if (isNegative)
-            string[size++] = '-';
-
-        string[size] = '\0';
-
-        std::reverse(string, string+size);
-
-        return size;
-    }
-
 private:
     Internal::StringDataLayout<Size> m_data;
 };