This change adds the capability for a resource provider to indicate
that, where an action carried out in response to a diff, a certain set
of properties would be "stable"; that is to say, they are guaranteed
not to change. As a result, properties may be resolved to their final
values during previewing, avoiding erroneous cascading impacts.
This avoids the ever-annoying situation I keep running into when demoing:
when adding or removing an ingress rule to a security group, we ripple
the impact through the instance, and claim it must be replaced, because
that instance depends on the security group via its name. Well, the name
is a great example of a stable property, in that it will never change, and
so this is truly unfortunate and always adds uncertainty into the demos.
Particularly since the actual update doesn't need to perform replacements.
This resolvespulumi/pulumi#330.
b7576b9b14