What happens if a rollback custom action fails? - wix

Question

What happens if a rollback custom action fails? Do I need to specify a Return attribute in Wix CustomAction element for a rollback custom action?
I did a quick test. I created a binary custom action:
This is a C++ code:
UINT __stdcall ForceInstallFailure(MSIHANDLE hModule)
{
return ERROR_INSTALL_FAILURE;
}
A Wix code:
<CustomAction Id="CA_ForceInstallFailure" BinaryKey="Bin_CAInst"
DllEntry="ForceInstallFailure"
Execute="rollback" Return="check" Impersonate="no" />
Wix translated it into type 3329:
Type 1 (DLL generated from a binary stream called through an entry point) +
3328 (msidbCustomActionTypeInScript + msidbCustomActionTypeNoImpersonate + msidbCustomActionTypeRollback)
I simulated a rollback with https://wixtoolset.org/docs/v3/customactions/wixfailwhendeferred/
This is what I get in MSI log:
Rollback: CA_ForceInstallFailure
MSI (s) (90:B4) [02:18:54:053]: Executing op: ActionStart(Name=CA_ForceInstallFailure,,)
MSI (s) (90:B4) [02:18:54:053]: Executing op: CustomActionRollback(Action=CA_ForceInstallFailure,ActionType=3329,Source=BinaryData,Target=ForceInstallFailure,)
MSI (s) (90:14) [02:18:54:053]: Invoking remote custom action. DLL: C:\Windows\Installer\MSIC523.tmp, Entrypoint: ForceInstallFailure
CustomAction CA_ForceInstallFailure returned actual error code 1603 but will be translated to success due to continue marking
It looks like Windows Installer doesn't check a custom action return value during a rollback, even though I didn't mark it specifically as Return="ignore" which would translate to msidbCustomActionTypeContinue addition.
Although it logically seems the correct behavior, I could not find any official documentation that describes this.

Answer 1

The Windows Installer does not have rollback for rollback, so it ignores custom action failures during rollback.