Fix PR33727: std::basic_stringbuf only works with DefaultConstructible allocators. Thanks to Jonathan Wakely for the report and suggested fix

llvm-svn: 309838

libcxx/include/sstream

@@ -249,7 +249,8 @@ basic_stringbuf<_CharT, _Traits, _Allocator>::basic_stringbuf(ios_base::openmode
 template <class _CharT, class _Traits, class _Allocator>
 basic_stringbuf<_CharT, _Traits, _Allocator>::basic_stringbuf(const string_type& __s,
                              ios_base::openmode __wch)
-    : __hm_(0),
+    : __str_(__s.get_allocator()),
+      __hm_(0),
       __mode_(__wch)
 {
     str(__s);

libcxx/test/std/input.output/string.streams/stringstream.cons/string.pass.cpp

@@ -18,6 +18,16 @@
 #include <sstream>
 #include <cassert>
 
+template<typename T>
+struct NoDefaultAllocator : std::allocator<T>
+{
+  template<typename U> struct rebind { using other = NoDefaultAllocator<U>; };
+  NoDefaultAllocator(int id) : id(id) { }
+  template<typename U> NoDefaultAllocator(const NoDefaultAllocator<U>& a) : id(a.id) { }
+  int id;
+};
+
+
 int main()
 {
     {
@@ -46,4 +56,13 @@ int main()
         ss << i << ' ' << 123;
         assert(ss.str() == L"456 1236 ");
     }
+    { // This is https://bugs.llvm.org/show_bug.cgi?id=33727
+		typedef std::basic_string   <char, std::char_traits<char>, NoDefaultAllocator<char> > S;
+		typedef std::basic_stringbuf<char, std::char_traits<char>, NoDefaultAllocator<char> > SB;
+
+		S s(NoDefaultAllocator<char>(1));
+		SB sb(s);
+	//	This test is not required by the standard, but *where else* could it get the allocator?
+		assert(sb.str().get_allocator() == s.get_allocator());
+    }
 }