Add comments and style fixes to <variant>

	* include/std/variant: Adjust whitespace. Add comments.
	(_Multi_array): Leave primary template undefined.
	(_Multi_array<_Tp>): Define partial specialization for base case of
	recursion.
	(__gen_vtable_impl, __gen_vtable): Remove redundant && from type
	which is always a reference.
	(__gen_vtable::_S_apply()): Remove function, inline body into
	default member initializer.
	* testsuite/20_util/variant/visit.cc: Test with noncopyable types.

From-SVN: r270238

libstdc++-v3/ChangeLog

 2019-04-09  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/variant: Adjust whitespace. Add comments.
+	(_Multi_array): Leave primary template undefined.
+	(_Multi_array<_Tp>): Define partial specialization for base case of
+	recursion.
+	(__gen_vtable_impl, __gen_vtable): Remove redundant && from type
+	which is always a reference.
+	(__gen_vtable::_S_apply()): Remove function, inline body into
+	default member initializer.
+	* testsuite/20_util/variant/visit.cc: Test with noncopyable types.
+
 	* include/std/variant (__variant_idx_cookie): Add member type.
 	(__visitor_result_type): Remove.
 	(__do_visit): Use invoke_result instead of __visitor_result_type.

libstdc++-v3/testsuite/20_util/variant/visit.cc

@@ -66,8 +66,30 @@ test01()
   VERIFY( res == 35 );
 }
 
+void
+test02()
+{
+  struct NoCopy
+  {
+    NoCopy() { }
+    NoCopy(const NoCopy&) = delete;
+    NoCopy(NoCopy&&) = delete;
+    ~NoCopy() { }
+
+    int operator()(int i) { return i; }
+    int operator()(const NoCopy&) { return 0; }
+  };
+
+  std::variant<NoCopy, int> v{1};
+  NoCopy f;
+  // Visit should not need arguments to be copyable:
+  int res = std::visit(f, v);
+  VERIFY( res == 1 );
+}
+
 int
 main()
 {
   test01();
+  test02();
 }