libstdc++: LWG 3397 basic_istream_view::iterator should not provide iterator_category

libstdc++-v3/ChangeLog:

	LWG 3397 basic_istream_view::iterator should not provide
	iterator_category
	* include/std/ranges (basic_istream_view:_Iterator::iterator_category):
	Rename to ...
	(basic_istream_view:_Iterator::iterator_concept): ... this.
	* testsuite/std/ranges/istream_view.cc: Augment test.

libstdc++-v3/ChangeLog

 2020-02-25  Patrick Palka  <ppalka@redhat.com>
 
+	LWG 3397 basic_istream_view::iterator should not provide
+	iterator_category
+	* include/std/ranges (basic_istream_view:_Iterator::iterator_category):
+	Rename to ...
+	(basic_istream_view:_Iterator::iterator_concept): ... this.
+	* testsuite/std/ranges/istream_view.cc: Augment test.
+
 	LWG 3325 Constrain return type of transformation function for
 	transform_view
 	* include/std/ranges (transform_view): Constrain the return type of the

libstdc++-v3/include/std/ranges

@@ -971,7 +971,7 @@ namespace views
       struct _Iterator
       {
       public:
-	using iterator_category = input_iterator_tag;
+	using iterator_concept = input_iterator_tag;
 	using difference_type = ptrdiff_t;
 	using value_type = _Val;
 

libstdc++-v3/testsuite/std/ranges/istream_view.cc

@@ -68,10 +68,26 @@ test03()
   VERIFY( ranges::equal(v, (int[]){0,1,2,3,4}) );
 }
 
+template<typename T>
+concept has_iterator_category = requires { typename T::iterator_category; };
+
+void
+test04()
+{
+  std::istringstream s("12345");
+  auto v = ranges::istream_view<char>(s);
+  // LWG 3397
+  using It = ranges::iterator_t<decltype(v)>;
+  static_assert(!has_iterator_category<It>);
+  static_assert(std::input_iterator<It>);
+  static_assert(!std::forward_iterator<It>);
+}
+
 int
 main()
 {
   test01();
   test02();
   test03();
+  test04();
 }