Fix "Expression depends on non-NOTIFYable properties" regression

CONSTANT properties are by nature non-NOTIFYable.

The issue behind the regression is caused by the fact that we were
capturing a property regardless of whether or not it was const.
There were two states that captureRequired was expressing:

true: We're reading the property of a QObject, and we're not quite sure
where the QObject comes from or what it is. So, when reading that
property at run-time, make sure that we capture where we read that
property so that if it changes we can re-evaluate the entire
expression.

false: We're reading the property of a QObject, and we know that it's
the scope object or context object, which we know very well. Instead of
registering a property capture every time, we can do that ahead of time
and then register all those captures in one shot in
registerQmlDependencies().

There is a third state that is only relevant when captureRequired is
false: We're reading a property from the scope or context object, but
it's a CONSTANT property, so we don't need to register a dependency
at all.

This patch adds replaces captureRequired with the PropertyCapturePolicy
enum, which accounts for the third state and, as a bonus, makes the
code easier to understand.

Task-number: QTBUG-66361
Change-Id: I6cef1deb76538fbdacf1324b4467403dd40dd7de
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 27 insertions, 5 deletions

diff --git a/src/qml/compiler/qv4codegen_p.h b/src/qml/compiler/qv4codegen_p.h
index 5c4ce14870..e52f63e1f4 100644
--- a/src/qml/compiler/qv4codegen_p.h
+++ b/src/qml/compiler/qv4codegen_p.h
@@ -219,6 +219,28 @@ public:
             return isStackSlot();
         }
 
+        enum PropertyCapturePolicy {
+            /*
+                We're reading a property from the scope or context object, but it's a CONSTANT property,
+                so we don't need to register a dependency at all.
+            */
+            DontCapture,
+            /*
+                We're reading the property of a QObject, and we know that it's the
+                scope object or context object, which we know very well. Instead of registering a
+                property capture every time, we can do that ahead of time and then register all those
+                captures in one shot in registerQmlDependencies().
+            */
+            CaptureAheadOfTime,
+            /*
+                We're reading the property of a QObject, and we're not quite sure where
+                the QObject comes from or what it is. So, when reading that property at run-time,
+                make sure that we capture where we read that property so that if it changes we can
+                re-evaluate the entire expression.
+            */
+            CaptureAtRuntime
+        };
+
         static Reference fromAccumulator(Codegen *cg) {
             return Reference(cg, Accumulator);
         }
@@ -267,20 +289,20 @@ public:
             r.isReadonly = true;
             return r;
         }
-        static Reference fromQmlScopeObject(const Reference &base, qint16 coreIndex, qint16 notifyIndex, bool captureRequired) {
+        static Reference fromQmlScopeObject(const Reference &base, qint16 coreIndex, qint16 notifyIndex, PropertyCapturePolicy capturePolicy) {
             Reference r(base.codegen, QmlScopeObject);
             r.qmlBase = base.storeOnStack().stackSlot();
             r.qmlCoreIndex = coreIndex;
             r.qmlNotifyIndex = notifyIndex;
-            r.captureRequired = captureRequired;
+            r.capturePolicy = capturePolicy;
             return r;
         }
-        static Reference fromQmlContextObject(const Reference &base, qint16 coreIndex, qint16 notifyIndex, bool captureRequired) {
+        static Reference fromQmlContextObject(const Reference &base, qint16 coreIndex, qint16 notifyIndex, PropertyCapturePolicy capturePolicy) {
             Reference r(base.codegen, QmlContextObject);
             r.qmlBase = base.storeOnStack().stackSlot();
             r.qmlCoreIndex = coreIndex;
             r.qmlNotifyIndex = notifyIndex;
-            r.captureRequired = captureRequired;
+            r.capturePolicy = capturePolicy;
             return r;
         }
         static Reference fromThis(Codegen *cg) {
@@ -336,7 +358,7 @@ public:
                 Moth::StackSlot qmlBase;
                 qint16 qmlCoreIndex;
                 qint16 qmlNotifyIndex;
-                bool captureRequired;
+                PropertyCapturePolicy capturePolicy;
             };
         };
         QString name;