On 5/28/20 7:23 PM, Marek Polacek wrote:
Barry pointed out to me that our braced-init-list as a template-argument
extension doesn't work as expected when we aggregate-initialize. Thus
fixed by calling digest_init in convert_nontype_argument so that we can
actually convert the CONSTRUCTOR.
I don't think we can call digest_init any earlier, and it needs to
happen before the call to build_converted_constant_expr.
Or we could fix build_converted_constant_expr to allow it; aggregate
list-initialization is a user-defined conversion sequence, so I tihnk it
should be allowed as part of a converted constant expression.
Jason
Barry also noticed that we allow designated initializers for
non-aggregate types in the template-argument argument context, i.e. this
struct S {
unsigned a;
unsigned b;
constexpr S(unsigned _a, unsigned _b) noexcept: a{_a}, b{_b} { }
};
template<S s> struct X { };
void f()
{
X<{.a = 1, .b = 2}> x;
}
probably should not compile. But I'm not too sure about it, and don't
know how I would fix it anyway, so I'm not dealing with it in this
patch.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
gcc/cp/ChangeLog:
PR c++/95369
* pt.c (convert_nontype_argument): In C++20, reshape and digest
a braced-init-list if the type is an aggregate.
gcc/testsuite/ChangeLog:
PR c++/95369
* g++.dg/cpp2a/nontype-class38.C: New test.
---
gcc/cp/pt.c | 13 +++++++++
gcc/testsuite/g++.dg/cpp2a/nontype-class38.C | 30 ++++++++++++++++++++
2 files changed, 43 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 90dafff3aa7..adb7593f77d 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -7133,6 +7133,19 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
return error_mark_node;
}
+ /* For a { } template argument, like in X<{ 1, 2 }>, we need to digest
+ here so that build_converted_constant_expr below is able to convert
+ it to TYPE. */
+ if (cxx_dialect >= cxx20
+ && BRACE_ENCLOSED_INITIALIZER_P (expr)
+ && CP_AGGREGATE_TYPE_P (type))
+ {
+ expr = reshape_init (type, expr, complain);
+ expr = digest_init (type, expr, complain);
+ if (expr == error_mark_node)
+ return error_mark_node;
+ }
+
/* If we are in a template, EXPR may be non-dependent, but still
have a syntactic, rather than semantic, form. For example, EXPR
might be a SCOPE_REF, rather than the VAR_DECL to which the
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
new file mode 100644
index 00000000000..5b440fd1c9e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class38.C
@@ -0,0 +1,30 @@
+// PR c++/95369
+// { dg-do compile { target c++20 } }
+
+struct S {
+ int a;
+ int b;
+};
+
+struct W {
+ int i;
+ S s;
+};
+
+template <S p>
+void fnc()
+{
+}
+
+template<S s> struct X { };
+template<W w> struct Y { };
+
+void f()
+{
+ fnc<{ .a = 10, .b = 20 }>();
+ fnc<{ 10, 20 }>();
+ X<{ .a = 1, .b = 2 }> x;
+ X<{ 1, 2 }> x2;
+ // Brace elision is likely to be allowed.
+ Y<{ 1, 2, 3 }> x3;
+}
base-commit: 3d8d5ddb539a5254c7ef83414377f4c74c7701d4
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index a51ebb5d9e3..d38e23a7e9a 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -4348,7 +4348,7 @@ build_converted_constant_expr_internal (tree type, tree expr,
and where the reference binding (if any) binds directly. */
for (conversion *c = conv;
- conv && c->kind != ck_identity;
+ c && c->kind != ck_identity;
c = next_conversion (c))
{
switch (c->kind)
@@ -4356,6 +4356,8 @@ build_converted_constant_expr_internal (tree type, tree expr,
/* A conversion function is OK. If it isn't constexpr, we'll
complain later that the argument isn't constant. */
case ck_user:
+ /* List-initialization is OK. */
+ case ck_aggr:
/* The lvalue-to-rvalue conversion is OK. */
case ck_rvalue:
/* Array-to-pointer and function-to-pointer. */
