Here, when substituting still-dependent args into an alias template, we see
a non-const type because the default argument is non-const, and is not a
template parm object because it's still dependent.
Tested x86_64-pc-linux-gnu, applying to trunk.
gcc/cp/ChangeLog:
PR c++/98810
* pt.c (tsubst_copy) [VIEW_CONVERT_EXPR]: Add const
to a class non-type template argument that needs it.
gcc/testsuite/ChangeLog:
PR c++/98810
* g++.dg/cpp2a/nontype-class-defarg1.C: New test.
---
gcc/cp/pt.c | 27 ++++++++++++-------
.../g++.dg/cpp2a/nontype-class-defarg1.C | 6 +++++
2 files changed, 24 insertions(+), 9 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class-defarg1.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 3576e0effb6..5fafee472a5 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -16826,18 +16826,27 @@ tsubst_copy (tree t, tree args, tsubst_flags_t
complain, tree in_decl)
{
/* Wrapper to make a C++20 template parameter object const. */
op = tsubst_copy (op, args, complain, in_decl);
- if (TREE_CODE (op) == TEMPLATE_PARM_INDEX)
+ if (!CP_TYPE_CONST_P (TREE_TYPE (op)))
{
+ /* The template argument is not const, presumably because
+ it is still dependent, and so not the const template parm
+ object. */
tree type = tsubst (TREE_TYPE (t), args, complain, in_decl);
- return build1 (code, type, op);
- }
- else
- {
- gcc_assert (CP_TYPE_CONST_P (TREE_TYPE (op))
- || (TREE_CODE (op) == IMPLICIT_CONV_EXPR
- && IMPLICIT_CONV_EXPR_NONTYPE_ARG (op)));
- return op;
+ gcc_checking_assert (same_type_ignoring_top_level_qualifiers_p
+ (type, TREE_TYPE (op)));
+ if (TREE_CODE (op) == CONSTRUCTOR
+ || TREE_CODE (op) == IMPLICIT_CONV_EXPR)
+ {
+ /* Don't add a wrapper to these. */
+ op = copy_node (op);
+ TREE_TYPE (op) = type;
+ }
+ else
+ /* Do add a wrapper otherwise (in particular, if op is
+ another TEMPLATE_PARM_INDEX). */
+ op = build1 (code, type, op);
}
+ return op;
}
/* force_paren_expr can also create a VIEW_CONVERT_EXPR. */
else if (code == VIEW_CONVERT_EXPR && REF_PARENTHESIZED_P (t))
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class-defarg1.C
b/gcc/testsuite/g++.dg/cpp2a/nontype-class-defarg1.C
new file mode 100644
index 00000000000..85e50ff8069
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class-defarg1.C
@@ -0,0 +1,6 @@
+// PR c++/98810
+// { dg-do compile { target c++20 } }
+
+template <auto> struct a {};
+template <int i, a <i> s = a <i> {}> using b = a <s>;
+template <int i> constexpr auto g (const b <i> &) { return true; };
base-commit: 28af4b9a7c5ee9f6c6fc111210639eb2f64bddcd
--
2.27.0
