c++: tweak constexpr union diagnostic

It's now possible to see an active member of a union that has not actually
been initialized, so let's clarify the diagnostic.

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_component_reference): Clarify diagnostic.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/constexpr-98122.C: Adjust diagnostic.
	* g++.dg/cpp26/constexpr-new6a.C: New test.

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 1621e28da5c867931ad8e14ca95f42e06e1516b4..6ebe6ebaef63fc38978d005a9932b9794e5bf6ba 100644 (file)
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -5788,7 +5788,7 @@ cxx_eval_component_reference (const constexpr_ctx *ctx, tree t,
              if (cep->value == NULL_TREE)
                error ("accessing uninitialized member %qD", part);
              else
-               error ("accessing %qD member instead of initialized %qD member "
+               error ("accessing %qD member instead of active %qD member "
                       "in constant expression", part, cep->index);
            }
          *non_constant_p = true;

diff --git a/gcc/testsuite/g++.dg/cpp26/constexpr-new6a.C b/gcc/testsuite/g++.dg/cpp26/constexpr-new6a.C
new file mode 100644 (file)
index 0000000..2e3b101
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/constexpr-new6a.C
@@ -0,0 +1,17 @@
+// { dg-do compile { target c++26 } }
+
+#include <new>
+
+union U { double d; int i; };
+
+constexpr int f()
+{
+  U u;
+  new (&u.i) int;
+  return u.d;                  // { dg-error "active" }
+}
+
+int main ()
+{
+  constexpr int i = f();       // { dg-message "" }
+}

diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-98122.C b/gcc/testsuite/g++.dg/cpp2a/constexpr-98122.C
index b0c91d5ef97ab72667669dabb5485a27c9aaeef8..d835602296c8cfa45f554e481c36d20beae82358 100644 (file)
--- a/gcc/testsuite/g++.dg/cpp2a/constexpr-98122.C
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-98122.C
@@ -9,7 +9,7 @@ bar ()
 {
   V f { .b = 42 };
   constexpr auto m = &V::a;
-  return (f.*m) == 42;  // { dg-error "accessing 'V::a' member instead of initialized 'V::b' member in constant expression" }
+  return (f.*m) == 42;  // { dg-error "accessing 'V::a' member instead of active 'V::b' member in constant expression" }
 }
 
 constexpr bool