Trigger uninstallation of downgraded application from managed bootstrapper code - wix

Question

Users of our managed bootstrapper installer should be able to downgrade the bundle in case a new version causes problems:
<MajorUpgrade Schedule="afterInstallValidate" AllowDowngrades="yes" AllowSameVersionUpgrades="no" />
When upgrading, the existing bundle is properly uninstalled. Only the new version remains in the list of installed programs in Programs and Features. The log confirms the chosen action:
OnDetectRelatedBundle(): Operation MajorUpgrade
OnDetectRelatedBundle(): RelationType Upgrade
Planned package: APP_MSI_PACKAGE, state: Absent, default requested: Present, ba requested: Present, execute: Install, …
Planned related bundle: { }, type: Upgrade, … execute: Uninstall, rollback: Install, dependency: None
When downgrading, the existing bundle remains in Programs and Features. According to the log, the type downgrade is recognized, but no Uninstall is planned:
OnDetectRelatedBundle(): Operation Downgrade
OnDetectRelatedBundle(): RelationType Upgrade
Planned package: APP_MSI_PACKAGE, state: Obsolete, default requested: None, ba requested: None, execute: None, …
Planned related bundle: {}, type: Upgrade … execute: None, rollback: None, dependency: None
There shouldn't be two entries for the same application in Programs and Features. After the downgrade I can uninstall the obsolete version manually, but the user should not have to do that.
I find it confusing that MajorUpgrade is part of <Product>, but then in Programs and Features the version is tracked for the entire bundle. I read somewhere that the same UpgradeCode should be used in Product and Bundle. Is that recommended? I tried the same UpgradeCode and separate UpgradeCodes. There seems to be no difference.
I’ve researched a bit and supposedly the uninstallation is not supported when downgrading. Is that true?
If it is not supported, how can I trigger the uninstallation of the related bundle manually from the managed bootstrapper code?
Truly, the problem boils down to the double entry in Programs and Features. If I cannot uninstall it, can I remove (or maybe hide, which I would consider a terrible hack) the obsolete version of the bundle via code some other way?

Answer 1

I had to determine if the setup installs a downgrade by using the event DetectRelatedBundle. Then in the event handler for PlanRelatedBundle I had to specify that the related bundle should be absent:
private void OnPlanRelatedBundle(object sender, PlanRelatedBundleEventArgs e)
{
if (BundleUpgrade || BundleDowngrade)
e.State = RequestState.Absent;
}
For good measure I set the absent state when an upgrade was detected as well even though that case already worked. Now the related bundle is removed in both cases.