This change supports displaying manifest information for a stack and
changes the way we handle Snapshots in our backend.
Previously, every call to GetStack would synthesize a Snapshot by
taking the set of resources returned from the
`/api/stacks/<owner>/<name>` endpoint, combined with an empty
manfiest (since the service was not returning the manifest).
This wasn't great for two reasons:
1. We didn't have manifest information, so we couldn't display any of
its information (most important the last updated time).
2. This strategy required that the service return all the resources
for a stack anytime GetStack was called. While the CLI did not
often need this detailed information the fact that we forced the
Service to produce it (which in the case of stack managed PPC would
require the service to talk to yet another service) creates a bunch
of work that we end up ignoring.
I've refactored the code such that `backend.Stack`'s `Snapshot()` method
now lazily requests the information from the service such that we can
construct a `Snapshot()` on demand and only pay the cost when we
actually need it.
I think making more of this stuff lazy is the long term direction we
want to follow.
Unfortunately, right now, it means in cases where we do need this data
we end up fetching it twice. The service does it once when we call
GetStack and then we do it again when we actually need to get at the
Snapshot. However, once we land this change, we can update the
service to no longer return resources on the apistack.Stack type. The
CLI no longer needs this property. We'll likely want to continue in a
direction where `apistack.Stack` can be created quickly by the
service (without expensive database queries or fetching remote
resources) and just add additional endpoints that let us get at the
specific information we want in the specific cases when we want it
instead of forcing us to return a bunch of data that we often ignore.
Fixespulumi/pulumi-service#371