[PATCH] c++: paren aggr CTAD with base classes [PR115114]

[Patrick Palka]

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look
OK for trunk and perhaps 14?

-- >8 --

We're accidentally ignoring base classes during parenthesized aggregate
CTAD because the TYPE_FIELDS of a template type doesn't contain bases,
so we need to consider them separately.

        PR c++/115114

gcc/cp/ChangeLog:

        * pt.cc (maybe_aggr_guide): Consider base classes in the paren
        init case.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/class-deduction-aggr15.C: New test.
---
 gcc/cp/pt.cc                                  |  7 ++++++
 .../g++.dg/cpp2a/class-deduction-aggr15.C     | 23 +++++++++++++++++++
 2 files changed, 30 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr15.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index d83f530ac8d..54d74989903 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -30202,6 +30202,13 @@ maybe_aggr_guide (tree tmpl, tree init, 
vec<tree,va_gc> *args)
   else if (TREE_CODE (init) == TREE_LIST)
     {
       int len = list_length (init);
+      for (tree binfo : BINFO_BASE_BINFOS (TYPE_BINFO (template_type)))
+       {
+         if (!len)
+           break;
+         parms = tree_cons (NULL_TREE, BINFO_TYPE (binfo), parms);
+         --len;
+       }
       for (tree field = TYPE_FIELDS (template_type);
           len;
           --len, field = DECL_CHAIN (field))
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr15.C 
b/gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr15.C
new file mode 100644
index 00000000000..16dc0f52b64
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-aggr15.C
@@ -0,0 +1,23 @@
+// PR c++/115114
+// { dg-do compile { target c++20 } }
+
+struct X {} x;
+struct Y {} y;
+
+template<class T, class U>
+struct A : T {
+  U m;
+};
+
+using ty1 = decltype(A{x, 42}); // OK
+using ty1 = decltype(A(x, 42)); // OK, used to fail
+using ty1 = A<X, int>;
+
+template<class T, class U = int, class V = int>
+struct B : T, V {
+  U m = 42;
+};
+
+using ty2 = decltype(B{x, y}); // OK
+using ty2 = decltype(B(x, y)); // OK, used to fail
+using ty2 = B<X, int, Y>;
-- 
2.45.1.190.g19fe900cfc