Protect exceptional paths under libcpp-no-exceptions

These tests are of the form

try {
   action-that-may-throw
   assert(!exceptional-condition)
   assert(some-other-facts)
 } catch (relevant-exception) {
   assert(exceptional-condition)
 }

Under libcpp-no-exceptions there is still value in verifying
some-other-facts while avoiding the exceptional case. So for these tests
just conditionally check some-other-facts if exceptional-condition is
false. When exception are supported make sure that a true
exceptional-condition throws an exception

Differential Revision: https://reviews.llvm.org/D26136

llvm-svn: 285697

libcxx/test/std/strings/basic.string/string.modifiers/string_erase/size_size.pass.cpp

@@ -7,7 +7,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// XFAIL: libcpp-no-exceptions
 // <string>
 
 // basic_string<charT,traits,Allocator>&
@@ -24,40 +23,58 @@ template <class S>
 void
 test(S s, typename S::size_type pos, typename S::size_type n, S expected)
 {
-    typename S::size_type old_size = s.size();
+    const typename S::size_type old_size = s.size();
     S s0 = s;
-    try
+    if (pos <= old_size)
     {
         s.erase(pos, n);
         LIBCPP_ASSERT(s.__invariants());
-        assert(pos <= old_size);
         assert(s == expected);
     }
-    catch (std::out_of_range&)
+#ifndef TEST_HAS_NO_EXCEPTIONS
+    else
     {
-        assert(pos > old_size);
-        assert(s == s0);
+        try
+        {
+            s.erase(pos, n);
+            assert(false);
+        }
+        catch (std::out_of_range&)
+        {
+            assert(pos > old_size);
+            assert(s == s0);
+        }
     }
+#endif
 }
 
 template <class S>
 void
 test(S s, typename S::size_type pos, S expected)
 {
-    typename S::size_type old_size = s.size();
+    const typename S::size_type old_size = s.size();
     S s0 = s;
-    try
+    if (pos <= old_size)
     {
         s.erase(pos);
         LIBCPP_ASSERT(s.__invariants());
-        assert(pos <= old_size);
         assert(s == expected);
     }
-    catch (std::out_of_range&)
+#ifndef TEST_HAS_NO_EXCEPTIONS
+    else
     {
-        assert(pos > old_size);
-        assert(s == s0);
+        try
+        {
+            s.erase(pos);
+            assert(false);
+        }
+        catch (std::out_of_range&)
+        {
+            assert(pos > old_size);
+            assert(s == s0);
+        }
     }
+#endif
 }
 
 template <class S>