Allow limited extensions to globals

We can allow

a, overriding data members of globals, such as Error.name
b, adding members that don't clash with any internals
c, any manipulation of toString(), toLocaleString(), valueOf(),
   and constructor

To that effect, add a "Locked" flag to our internal classes. If that is
set, disallow changing prototypes and when defining a property, check if
it shadows any non-configurable property. Furthermore, make all
non-primitive properties that are not meant to be overridden
non-configurable and non-writable.

constructor, toString(), toLocaleString() and valueOf() are exempt
because they are explicitly meant to be overridden by users. Therefore,
we let that happen and refrain from optimizing them or triggering their
implicit invocation in optimized code.

[ChangeLog][QtQml][Important Behavior Changes] The JavaScript global
objects are not frozen anymore in a QML engine. Instead, they are
selectively locked. You can extend the objects with new members as long
as you don't shadow any existing methods, and you can change or override
data members. This also means that most methods of Object.prototype,
which was previously exempt from the freezing, cannot be changed
anymore. You can, however, change or override constructor, toString(),
toLocaleString() and valueOf() on any prototype. Those are clearly meant
to be overridden by user code.

Fixes: QTBUG-101298
Task-number: QTBUG-84341
Change-Id: Id77db971f76c8f48b18e7a93607da5f947ecfc3e
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

0 files changed, 0 insertions, 0 deletions