[libc++][test] Silence MSVC warning

[CaseyCarter]

Summary

Our static analyzer likes to warn when loop bodies are never executed, which is true for make_string<T>(""). Build the result with basic_string's iterator-pair constructor instead, which is simpler (one liner), faster (single pass), and doesn't trigger the warning.

[philnik]

LGTM

libcxx/test/std/ranges/range.factories/range.istream.view/utils.h

9

Seems even simpler.

[CaseyCarter]

libcxx/test/std/ranges/range.factories/range.istream.view/utils.h

9

The (pointer, length) constructor would only work when CharT is char, this works for any CharT to which a const char lvalue converts. Most notably that includes basic_string<wchar_t> which the tests use.

libcxx/test/std/ranges/range.factories/range.istream.view/utils.h

 #ifndef TEST_STD_RANGES_RANGE_FACTORIES_RANGE_ISTREAM_UTILS_H
 #define TEST_STD_RANGES_RANGE_FACTORIES_RANGE_ISTREAM_UTILS_H
 
 #include <sstream>
 #include <string>
 
 template <class CharT, std::size_t N>
 auto make_string(const char (&in)[N]) {
-  std::basic_string<CharT> r(N - 1, static_cast<CharT>(0));
-  for (std::size_t i = 0; i < N - 1; ++i) {
-    r[i] = static_cast<CharT>(in[i]);
-  }
-  return r;
+  return std::basic_string<CharT>(in + 0, in + (N - 1));
 }
 
 template <class CharT, std::size_t N>
 auto make_string_stream(const char (&in)[N]) {
   return std::basic_istringstream<CharT>(make_string<CharT>(in));
 }
 
 #endif //TEST_STD_RANGES_RANGE_FACTORIES_RANGE_ISTREAM_UTILS_H