I don't think any of these changes are ABI-compatible?

I don't understand the bug being fixed.

We have:

Q_DISABLE_COPY(KModifierKeyInfo)

So why does KModifierKeyInfo::Private need to be shared?

So why does KModifierKeyInfo::Private need to be shared?

It needs to be refcounted. In 0fe2990dbad992a4925a7b7bee09b1cdfbe5a7a7 a plugin infrastructure was introduced. Unbeknownst to us the instances are shared internally by Qt.

KModifierKeyInfoProvider* createProvider()
{
    QPluginLoader loader(QStringLiteral("kf5/kguiaddons/kmodifierkey/kmodifierkey_")+qGuiApp->platformName());
    auto instance = dynamic_cast<KModifierKeyInfoProvider*>(loader.instance());
    if (instance)
        return instance;
...
 
 KModifierKeyInfo::KModifierKeyInfo(QObject *parent)
    : QObject(parent), p(createProvider())

The instance returned is the same every time despite the QPluginLoader being on the stack.
Now the destructor of KModifierKeyInfo cleans up p and if you have two instances of KModifierKeyInfo, which Kile does for instance, it crashes on double delete.

In D22241#490562, @broulik wrote:

I don't think any of these changes are ABI-compatible?

Yes it is, we're just modifying the size of a private class.

Also this was never released yet.

Landing because it works and we want it in before the freeze.