Fix PR#25973 : 'basic_string::assign(InputIt, InputIt) doesn't provide the strong exception safety guarantee'. This turned out to be a pervasive problem in <string>, which required a fair amount of rework. Add in an optimization for when iterators provide noexcept increment/comparison/assignment/dereference (which covers many of the iterators in libc++). Reviewed as http://reviews.llvm.org/D15862

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@257682 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/strings/iterators.exceptions.pass.cpp

@@ -0,0 +1,75 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+//
+
+// <iterator>
+
+// __libcpp_is_trivial_iterator<Tp>
+
+// __libcpp_string_gets_noexcept_iterator determines if an iterator can be used
+// w/o worrying about whether or not certain operations can throw.
+// This gives us a "fast path for string operations"
+//
+
+#include <iterator>
+#include <cassert>
+#include <string>
+#include <vector>
+#include <initializer_list>
+
+#include "test_iterators.h"
+
+int main()
+{
+//  basic tests
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<char *>::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<const char *>::value), "");
+    
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::move_iterator<char *> >      ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::move_iterator<const char *> >::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::reverse_iterator<char *> >      ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::reverse_iterator<const char *> >::value), "");
+    
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::__wrap_iter<char *> >      ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::__wrap_iter<const char *> >::value), "");
+    
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::reverse_iterator<std::__wrap_iter<char *> > > ::value), "");
+    
+//  iterators in the libc++ test suite
+    static_assert((!std::__libcpp_string_gets_noexcept_iterator<output_iterator       <char *> >::value), "");
+    static_assert((!std::__libcpp_string_gets_noexcept_iterator<input_iterator        <char *> >::value), "");
+    static_assert((!std::__libcpp_string_gets_noexcept_iterator<forward_iterator      <char *> >::value), "");
+    static_assert((!std::__libcpp_string_gets_noexcept_iterator<bidirectional_iterator<char *> >::value), "");
+    static_assert((!std::__libcpp_string_gets_noexcept_iterator<random_access_iterator<char *> >::value), "");
+    static_assert((!std::__libcpp_string_gets_noexcept_iterator<ThrowingIterator      <char *> >::value), "");
+    
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<NonThrowingIterator   <char *> >::value), "");
+	
+//
+//  iterators from libc++'s containers
+//
+
+//  string
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::vector<char>::iterator>              ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::vector<char>::const_iterator>        ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::vector<char>::reverse_iterator>      ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::vector<char>::const_reverse_iterator>::value), "");
+
+//  vector
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::basic_string<char>::iterator>              ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::basic_string<char>::const_iterator>        ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::basic_string<char>::reverse_iterator>      ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::basic_string<char>::const_reverse_iterator>::value), "");
+
+#ifndef _LIBCPP_HAS_NO_GENERALIZED_INITIALIZERS
+//  Initializer list  (which has no reverse iterators)
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::initializer_list<char>::iterator>              ::value), "");
+    static_assert(( std::__libcpp_string_gets_noexcept_iterator<std::initializer_list<char>::const_iterator>        ::value), "");
+#endif
+}