Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk?
-- >8 --
Here during ahead of time coercion of the variable template-id v1<int>,
since we pass only the innermost arguments to coerce_template_parms (and
outer arguments are still dependent at this point), substitution of the
default template argument V=U prematurely lowers U from level 2 to level 1.
Thus we incorrectly resolve v1<int> to v1<int, T> (effectively) instead
of to v1<int, int>.
Coercion of a class/alias template-id on the other hand is always done
using the full set of arguments relative to the most general template,
so ahead of time coercion there does the right thing. I suppose we
should do the same for variable template-ids.
PR c++/110580
gcc/cp/ChangeLog:
* pt.cc (lookup_template_variable): Pass all arguments to
coerce_template_parms, and use the innermost parameters from
the most general template.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/var-templ83.C: New test.
---
gcc/cp/pt.cc | 4 +++-
gcc/testsuite/g++.dg/cpp1y/var-templ83.C | 16 ++++++++++++++++
2 files changed, 19 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/var-templ83.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 076f788281e..fa15b75b9c5 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -10345,7 +10345,9 @@ lookup_template_variable (tree templ, tree arglist,
tsubst_flags_t complain)
if (flag_concepts && variable_concept_p (templ))
return build_concept_check (templ, arglist, tf_none);
- tree parms = DECL_INNERMOST_TEMPLATE_PARMS (templ);
+ tree gen_templ = most_general_template (templ);
+ tree parms = DECL_INNERMOST_TEMPLATE_PARMS (gen_templ);
+ arglist = add_outermost_template_args (templ, arglist);
arglist = coerce_template_parms (parms, arglist, templ, complain);
if (arglist == error_mark_node)
return error_mark_node;
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ83.C
b/gcc/testsuite/g++.dg/cpp1y/var-templ83.C
new file mode 100644
index 00000000000..f5268f258d7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ83.C
@@ -0,0 +1,16 @@
+// PR c++/110580
+// { dg-do compile { target c++14 } }
+
+template<class T>
+struct A {
+ template<typename U, typename V = U>
+ static constexpr bool v1 = __is_same(U, V);
+
+ template<typename U, typename V = T>
+ static constexpr bool v2 = !__is_same(U, V);
+
+ static_assert(v1<int>, "");
+ static_assert(v2<int>, "");
+};
+
+template struct A<char>;
--
2.41.0.327.gaa9166bcc0
