On Mon, Jan 07, 2019 at 09:52:55PM -0500, Jason Merrill wrote:
> On 1/7/19 6:56 PM, Marek Polacek wrote:
> > At the risk of seeming overly eager, I thought it would be reasonable to
> > go with the following: enabling braced-init-list as a template-argument.
> > As the discussion on the reflector clearly indicates, this was the intent
> > from the get-go.
> >
> > I know, it's not a regression. But I restricted the change to C++20, and it
> > should strictly allow code that wasn't accepted before -- when a template
> > argument starts with {. Perhaps we could even drop the C++20 check.
> >
> > What's your preference?
>
> Let's keep the C++20 check for now at least. I'd suggest moving the change
> further down, with this code:
Okay. I've experimented with checking expr_non_constant_p, but this version
gives better diagnostics.
Bootstrapped/regtested running on x86_64-linux, ok for trunk if it passes?
2019-01-08 Marek Polacek <pola...@redhat.com>
PR c++/88538 - braced-init-list in template-argument-list.
* parser.c (cp_parser_template_argument): Handle braced-init-list when
in C++20.
* g++.dg/cpp2a/nontype-class11.C: New test.
diff --git gcc/cp/parser.c gcc/cp/parser.c
index bca1739ace3..87f37d8ab2b 100644
--- gcc/cp/parser.c
+++ gcc/cp/parser.c
@@ -17020,6 +17020,18 @@ cp_parser_template_argument (cp_parser* parser)
argument = cp_parser_constant_expression (parser);
else
{
+ /* In C++20, we can encounter a braced-init-list. */
+ if (cxx_dialect >= cxx2a
+ && cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE))
+ {
+ cp_parser_parse_tentatively (parser);
+ bool expr_non_constant_p;
+ argument = cp_parser_braced_list (parser, &expr_non_constant_p);
+ if (cp_parser_parse_definitely (parser))
+ /* Yup, it was a braced-init-list. */
+ return argument;
+ }
+
/* With C++17 generalized non-type template arguments we need to handle
lvalue constant expressions, too. */
argument = cp_parser_assignment_expression (parser);
diff --git gcc/testsuite/g++.dg/cpp2a/nontype-class11.C
gcc/testsuite/g++.dg/cpp2a/nontype-class11.C
new file mode 100644
index 00000000000..8a06d23904b
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/nontype-class11.C
@@ -0,0 +1,21 @@
+// PR c++/88538
+// { dg-do compile { target c++2a } }
+
+struct S {
+ unsigned a;
+ unsigned b;
+ constexpr S(unsigned _a, unsigned _b) noexcept: a{_a}, b{_b} { }
+};
+
+template <S p>
+void fnc()
+{
+}
+
+template<S s> struct X { };
+
+void f()
+{
+ fnc<{10,20}>();
+ X<{1, 2}> x;
+}
