libstdc++: Do not expose set_brackets/set_separator for formatter with format_kind other than sequence [PR119861]

The standard defines separate specializations of range-default-formatter, out
of which only one for range_format::sequence provide the set_brackets and
set_separator methods. We implemented it as one specialization and exposed
this method for range_format other than string or debug_string, i.e. when
range_formatter was used as underlying formatter.

	PR libstdc++/119861

libstdc++-v3/ChangeLog:

	* include/std/format (formatter<_Rg, _CharT>::set_separator)
	(formatter<_Rg, _CharT>::set_brackets): Constrain with
	(format_kind<_Rg> == range_format::sequence).
	* testsuite/std/format/ranges/pr119861_neg.cc: New test.

1 files changed, 52 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/std/format/ranges/pr119861_neg.cc b/libstdc++-v3/testsuite/std/format/ranges/pr119861_neg.cc
new file mode 100644
index 0000000..9a6ed16
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/format/ranges/pr119861_neg.cc
@@ -0,0 +1,52 @@
+// { dg-do compile { target c++23 } }
+
+#include <format>
+#include <vector>
+
+// only format_kind::sequence provides set_brackets and set_separator methods 
+
+template<std::range_format fk, typename T>
+struct MyCont : std::vector<T>
+{
+  using std::vector<T>::vector;
+};
+
+template<std::range_format fk, typename T>
+constexpr std::range_format std::format_kind<MyCont<fk, T>> = fk;
+
+void test_sequence()
+{
+  std::formatter<MyCont<std::range_format::sequence, int>, char> fmtter;
+  fmtter.set_brackets("{", "}");
+  fmtter.set_separator(",");
+}
+
+void test_map()
+{
+  std::formatter<MyCont<std::range_format::map, std::pair<int, int>>, char> fmtter;
+  fmtter.set_brackets("{", "}"); // { dg-error "here" }
+  fmtter.set_separator(","); // { dg-error "here" }
+}
+
+void test_set()
+{
+  std::formatter<MyCont<std::range_format::set, int>, char> fmtter;
+  fmtter.set_brackets("{", "}"); // { dg-error "here" }
+  fmtter.set_separator(","); // { dg-error "here" }
+}
+
+void test_string()
+{
+  std::formatter<MyCont<std::range_format::string, char>, char> fmtter;
+  fmtter.set_brackets("{", "}"); // { dg-error "here" }
+  fmtter.set_separator(","); // { dg-error "here" }
+}
+
+void test_debug_string()
+{
+  std::formatter<MyCont<std::range_format::debug_string, char>, char> fmtter;
+  fmtter.set_brackets("{", "}"); // { dg-error "here" }
+  fmtter.set_separator(","); // { dg-error "here" }
+}
+
+// { dg-error "no matching function for call to 'std::formatter<" "" { target *-*-* } 0 }