More of P0600 - '[[nodiscard]] in the Library' mark empty() as nodiscard in string, string_view, and the free function std::empty(). Removed tabs from <string_view>, which is why the diff is so big.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@318328 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/basic.string/string.capacity/empty.fail.cpp

@@ -0,0 +1,28 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <string>
+
+// class deque
+
+// bool empty() const noexcept;
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+// UNSUPPORTED: clang-3.3, clang-3.4, clang-3.5, clang-3.6, clang-3.7, clang-3.8
+
+#include <string>
+
+#include "test_macros.h"
+
+int main ()
+{
+    std::string c;
+    c.empty();  // expected-error {{ignoring return value of function declared with 'nodiscard' attribute}}
+}

test/std/strings/basic.string/string.capacity/empty.pass.cpp

@@ -9,17 +9,19 @@
 
 // <string>
 
-// bool empty() const;
+// bool empty() const noexcept;
 
 #include <string>
 #include <cassert>
 
+#include "test_macros.h"
 #include "min_allocator.h"
 
 template <class S>
 void
 test(const S& s)
 {
+    ASSERT_NOEXCEPT(s.empty());
     assert(s.empty() == (s.size() == 0));
 }