Create a special "destroyed" type rather than using null

When a QPDF is destroyed, changing indirect objects to direct nulls
makes them effectively disappear silently when they sneak into other
places. Instead, we should treat this as an error. Adding a destroyed
object type makes this possible.

1 files changed, 8 insertions, 0 deletions

diff --git a/libqpdf/QPDFValueProxy.cc b/libqpdf/QPDFValueProxy.cc
index 461d8177..befaaf8b 100644
--- a/libqpdf/QPDFValueProxy.cc
+++ b/libqpdf/QPDFValueProxy.cc
@@ -1,6 +1,7 @@
 #include <qpdf/QPDFValueProxy.hh>
 
 #include <qpdf/QPDF.hh>
+#include <qpdf/QPDF_Destroyed.hh>
 
 void
 QPDFValueProxy::doResolve()
@@ -8,3 +9,10 @@ QPDFValueProxy::doResolve()
     auto og = value->og;
     QPDF::Resolver::resolve(value->qpdf, og);
 }
+
+void
+QPDFValueProxy::destroy()
+{
+    // See comments in reset() for why this isn't part of reset.
+    value = QPDF_Destroyed::getInstance();
+}