Here we fail to compile the attached test, stating that the use of
T<s> in T<s>::T() {} is "invalid use of incomplete type". It is a
function definition so grokdeclarator checks that the qualifying type
is complete.
When we parsed the class T, finish_struct gave the class a non-null
TYPE_SIZE, making it COMPLETE_TYPE_P. But then we're parsing T<s>,
a TEMPLATE_ID, in
T<s>::T() {}
so try to lookup_template_class T. This failed because we couldn't
find such a class: comp_template_args told us that the argument lists
don't match, because one of the args was wrapped in a VIEW_CONVERT_EXPR
to make it look const. It seems to me that we should see through
these artificial wrappers and consider the args same.
Bootstrapped/regtested on x86_64-linux, ok for trunk and maybe 9?
2020-01-29 Marek Polacek <pola...@redhat.com>
PR c++/91754 - Fix template arguments comparison with class NTTP.
* pt.c (class_nttp_const_wrapper_p): New.
(template_args_equal): See through class_nttp_const_wrapper_p
arguments.
* g++.dg/cpp2a/nontype-class30.C: New test.
---
gcc/cp/pt.c | 18 ++++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/nontype-class30.C | 15 +++++++++++++++
2 files changed, 33 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class30.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index e889c800aca..711da0fd053 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -8983,6 +8983,19 @@ coerce_innermost_template_parms (tree parms,
return coerced_args;
}
+/* Returns true if T is a wrapper to make a C++20 template parameter
+ object const. */
+
+static bool
+class_nttp_const_wrapper_p (tree t)
+{
+ if (cxx_dialect < cxx2a)
+ return false;
+ return (TREE_CODE (t) == VIEW_CONVERT_EXPR
+ && CP_TYPE_CONST_P (TREE_TYPE (t))
+ && TREE_CODE (TREE_OPERAND (t, 0)) == TEMPLATE_PARM_INDEX);
+}
+
/* Returns 1 if template args OT and NT are equivalent. */
int
@@ -8995,6 +9008,11 @@ template_args_equal (tree ot, tree nt, bool
partial_order /* = false */)
if (nt == any_targ_node || ot == any_targ_node)
return true;
+ if (class_nttp_const_wrapper_p (nt))
+ nt = TREE_OPERAND (nt, 0);
+ if (class_nttp_const_wrapper_p (ot))
+ ot = TREE_OPERAND (ot, 0);
+
if (TREE_CODE (nt) == TREE_VEC)
/* For member templates */
return TREE_CODE (ot) == TREE_VEC && comp_template_args (ot, nt);
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class30.C
b/gcc/testsuite/g++.dg/cpp2a/nontype-class30.C
new file mode 100644
index 00000000000..b2e174c7fd3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class30.C
@@ -0,0 +1,15 @@
+// PR c++/91754 - Fix template arguments comparison with class NTTP.
+// { dg-do compile { target c++2a } }
+
+struct S {};
+
+template<S s>
+struct T {
+ T();
+};
+
+template<S s>
+T<s>::T() {}
+
+S s;
+T<s> t;
base-commit: 989a5fb3aa5cb241727922c669da6742d33a7a86
--
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
