Scanner: Generate code that cleans up m_resource

The object that owns the resource will not be necessarily destroyed in
the destroy_resource() function. One such case may arise if the
compositor wants to animate the disappearing of a window, in that case
we want to keep client buffer data around even after the wl_buffer
resource has been destroyed.

If the compositor accidentally accesses the destroyed resource, it'll
most likely crash because of SIGSEGV. Speaking from my experience, such
crashes are far from being fun to debug.

With this change, qtwaylandscanner will generate code that cleans up
m_resource when the associated resource has been destroyed. It can be
useful for the purpose of preventing accessing already destroyed data.

Note that we want m_resource to be valid when the destroy_resource()
func is called because the compositor may need it in order to properly
perform cleanup, for example send a wl_pointer::leave() event, etc.

Pick-to: 5.15
Change-Id: I82dab3b7eae8c282fdbad689af49622350b6c867
Reviewed-by: David Edmundson <davidedmundson@kde.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/qtwaylandscanner/qtwaylandscanner.cpp b/src/qtwaylandscanner/qtwaylandscanner.cpp
index e984b8684..5b5694119 100644
--- a/src/qtwaylandscanner/qtwaylandscanner.cpp
+++ b/src/qtwaylandscanner/qtwaylandscanner.cpp
@@ -810,6 +810,8 @@ bool Scanner::process()
             printf("        %s *that = resource->%s_object;\n", interfaceName, interfaceNameStripped);
             printf("        that->m_resource_map.remove(resource->client(), resource);\n");
             printf("        that->%s_destroy_resource(resource);\n", interfaceNameStripped);
+            printf("        if (that->m_resource == resource)\n");
+            printf("            that->m_resource = nullptr;\n");
             printf("        delete resource;\n");
             printf("    }\n");
             printf("\n");