[PATCH 1/4] c++: Fix ICE with variadic concepts and aliases [PR93907]

[Patrick Palka]

This patch (naively) extends the PR93907 fix to also apply to variadic
concepts invoked with a type argument pack.  Without this, we ICE on
the below testcase (a variadic version of concepts-using2.C) in the same
manner as we used to on concepts-using2.C before r10-7133.

Patch series bootstrapped and regtested on x86_64-pc-linux-gnu,
and also tested against cmcstl2 and range-v3.

gcc/cp/ChangeLog:

	PR c++/93907
	* constraint.cc (tsubst_parameter_mapping): Also canonicalize
	the type arguments of a TYPE_ARGUMENT_PACk.

gcc/testsuite/ChangeLog:

	PR c++/93907
	* g++.dg/cpp2a/concepts-using3.C: New test, based off of
	concepts-using2.C.
---
 gcc/cp/constraint.cc                         | 10 ++++
 gcc/testsuite/g++.dg/cpp2a/concepts-using3.C | 52 ++++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-using3.C

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index b6f6f0d02a5..c871a8ab86a 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -2252,6 +2252,16 @@ tsubst_parameter_mapping (tree map, tree args, subst_info info)
 	  new_arg = tsubst_template_arg (arg, args, complain, in_decl);
 	  if (TYPE_P (new_arg))
 	    new_arg = canonicalize_type_argument (new_arg, complain);
+	  if (TREE_CODE (new_arg) == TYPE_ARGUMENT_PACK)
+	    {
+	      tree pack_args = ARGUMENT_PACK_ARGS (new_arg);
+	      for (int i = 0; i < TREE_VEC_LENGTH (pack_args); i++)
+		{
+		  tree& pack_arg = TREE_VEC_ELT (pack_args, i);
+		  if (TYPE_P (pack_arg))
+		    pack_arg = canonicalize_type_argument (pack_arg, complain);
+		}
+	    }
 	}
       if (new_arg == error_mark_node)
 	return error_mark_node;
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-using3.C b/gcc/testsuite/g++.dg/cpp2a/concepts-using3.C
new file mode 100644
index 00000000000..2c8ad40d104
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-using3.C
@@ -0,0 +1,52 @@
+// PR c++/93907
+// { dg-options -std=gnu++20 }
+
+// This testcase is a variadic version of concepts-using2.C; the only
+// difference is that 'cd' and 'ce' are now variadic concepts.
+
+template <int a> struct c {
+  static constexpr int d = a;
+  typedef c e;
+};
+template <typename> struct f;
+template <typename b> using g = typename f<b>::e;
+struct b;
+template <typename b> struct f { using e = b; };
+template <typename ai> struct m { typedef g<ai> aj; };
+template <typename b> struct n { typedef typename m<b>::aj e; };
+template <typename b> using an = typename n<b>::e;
+template <typename> constexpr bool ao = c<true>::d;
+template <typename> constexpr bool i = c<1>::d;
+template <typename> concept bb = i<b>;
+#ifdef __SIZEOF_INT128__
+using cc = __int128;
+#else
+using cc = long long;
+#endif
+template <typename...> concept cd = bb<cc>;
+template <typename... bt> concept ce = requires { requires cd<bt...>; };
+template <typename bt> concept h = ce<bt>;
+template <typename bt> concept l = h<bt>;
+template <typename> concept cl = ao<b>;
+template <typename b> concept cp = requires(b j) {
+  requires h<an<decltype(j.begin())>>;
+};
+struct o {
+  template <cl b> requires cp<b> auto operator()(b) {}
+};
+template <typename b> using cm = decltype(o{}(b()));
+template <typename bt> concept ct = l<bt>;
+template <typename da> concept dd = ct<cm<da>>;
+template <typename da> concept de = dd<da>;
+struct {
+  template <de da, typename b> void operator()(da, b);
+} di;
+struct p {
+  void begin();
+};
+template <typename> using df = p;
+template <int> void q() {
+  df<int> k;
+  int d;
+  di(k, d);
+}
-- 
2.29.2.154.g7f7ebe054a