[PATCH] c++: Reject union std::initializer_list [PR102434]

[Marek Polacek via Gcc-patches]

Weird things are going to happen if you define your std::initializer_list
as a union.  In this case, we crash in output_constructor_regular_field.

Let's not allow such a definition in the first place.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

        PR c++/102434

gcc/cp/ChangeLog:

        * class.cc (finish_struct): Don't allow union initializer_list.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp0x/initlist128.C: New test.
---
 gcc/cp/class.cc                          |  2 ++
 gcc/testsuite/g++.dg/cpp0x/initlist128.C | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/initlist128.C

diff --git a/gcc/cp/class.cc b/gcc/cp/class.cc
index 5db3722ae46..696155714e8 100644
--- a/gcc/cp/class.cc
+++ b/gcc/cp/class.cc
@@ -7766,6 +7766,8 @@ finish_struct (tree t, tree attributes)
                ok = true;
            }
        }
+      /* It also cannot be a union.  */
+      ok &= NON_UNION_CLASS_TYPE_P (t);
       if (!ok)
        fatal_error (input_location, "definition of %qD does not match "
                     "%<#include <initializer_list>%>", TYPE_NAME (t));
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist128.C 
b/gcc/testsuite/g++.dg/cpp0x/initlist128.C
new file mode 100644
index 00000000000..22246860f4e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist128.C
@@ -0,0 +1,16 @@
+// PR c++/102434
+// { dg-do compile { target c++11 } }
+
+using size_t = decltype(sizeof 0);
+
+namespace std {
+  template<typename T> union initializer_list { // { dg-error "definition of 
.*std::initializer_list.* does not match" }
+    const T *ptr;
+    size_t n;
+  };
+}
+template<typename T>
+void Task() {}
+auto b = { &Task<int> };
+
+// { dg-prune-output "compilation terminated" }

base-commit: f6f2d6cfec1c2fe9570b98211be58329d8d7749b
-- 
2.34.1