How does std::string(something) declare a variable

Why does std::string(whatever) declare a variable named whatever? Why isn't that expression treated as a constructor call and error out?

#include <string>

int main() {

    std::string(something);

    another += "something";
    static_assert(std::is_same<decltype(something), std::string>::value, "");
    assert(another == "something");

    return 0;
}

I am compiling with C++14 with the following compiler version

Apple LLVM version 8.1.0 (clang-802.0.42)
Target: x86_64-apple-darwin16.6.0
Thread model: posix
InstalledDir: /Applications/Xcode_8.3.3_fb.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin