vala: Non-nullable value-type in coalesce expression needs to be copied

The code generated by the coalesce expression could lead to stale
pointers to the stack if the right-side expression is an immediate value
(such as an integer literal or a struct).

Fixes https://gitlab.gnome.org/GNOME/vala/issues/893

1 files changed, 6 insertions, 0 deletions

diff --git a/vala/valabinaryexpression.vala b/vala/valabinaryexpression.vala
index fe559e1d5..927ca5413 100644
--- a/vala/valabinaryexpression.vala
+++ b/vala/valabinaryexpression.vala
@@ -234,6 +234,12 @@ public class Vala.BinaryExpression : Expression {
 				local_type = right.value_type.copy ();
 			}
 
+			if (local_type != null && right.value_type is ValueType && !right.value_type.nullable) {
+				// immediate values in the right expression must always be boxed,
+				// otherwise the local variable may receive a stale pointer to the stack
+				local_type.value_owned = true;
+			}
+
 			var local = new LocalVariable (local_type, get_temp_name (), left, source_reference);
 			var decl = new DeclarationStatement (local, source_reference);