Implement proposed resolution for LWG#2758. Reviewed as D24446. Normally, I would wait for these to be voted upon at a committee meeting (November), but the current draft standard is broken, and this should fix it. (And if it doesn't, we want to know about it soonest)

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@282342 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/basic.string/string.modifiers/string_append/T_size_size.pass.cpp

@@ -10,9 +10,8 @@
 // XFAIL: libcpp-no-exceptions
 // <string>
 
-// basic_string<charT,traits,Allocator>&
-//   append(basic_string_view<charT,traits> sv, size_type pos, size_type n = npos);
-//  the "= npos" was added for C++14
+// template <class T>
+//    basic_string& append(const T& t, size_type pos, size_type n=npos); // C++17
 
 #include <string>
 #include <string>
@@ -121,4 +120,61 @@ int main()
     test_npos(S(), SV("12345"), 5, S(""));
     test_npos(S(), SV("12345"), 6, S("not happening"));
     }
+    {
+    typedef std::string S;
+    typedef std::string_view SV;
+    S s;
+    SV sv = "EFGH";
+    char arr[] = "IJKL";
+
+    s.append("CDEF", 0);    // calls append(const char *, len)
+    assert(s == "");
+    s.clear();
+
+    s.append("QRST", 0, std::string::npos); // calls append(string("QRST"), pos, npos)
+    assert(s == "QRST");
+    s.clear();
+
+    s.append(sv, 0);  // calls append(T, pos, npos)
+    assert(s == sv);
+    s.clear();
+    
+    s.append(sv, 0, std::string::npos);   // calls append(T, pos, npos)
+    assert(s == sv);
+    s.clear();
+
+    s.append(arr, 0);     // calls append(const char *, len)
+    assert(s == "");
+    s.clear();
+
+    s.append(arr, 0, std::string::npos);    // calls append(string("IJKL"), pos, npos)
+    assert(s == "IJKL");
+    s.clear();
+
+    s.append(arr, 0);     // calls append(const char *, len)
+    assert(s == "");
+    s.clear();
+
+    {
+    S s = "ABCD";
+    SV sv = s;
+    s.append(sv);
+    assert(s == "ABCDABCD");
+
+    sv = s;
+    s.append(sv, 0, std::string::npos);
+    assert(s == "ABCDABCDABCDABCD");
+    }
+    
+    {
+    S s = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+    SV sv = s;
+    s.append(sv);
+    assert(s == "ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ");
+
+    sv = s;
+    s.append(sv, 0, std::string::npos);
+    assert(s == "ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ");
+    }
+    }
 }