This change adds an engine gRPC interface, and associated implementation,
so that plugins may do interesting things that require "phoning home".
Previously, the engine would fire up plugins and talk to them directly,
but there was no way for a plugin to ask the engine to do anything.
The motivation here is so that plugins can read evaluator state, such
as config information, but this change also allows richer logging
functionality than previously possible. We will still auto-log any
stdout/stderr writes; however, explicit errors, warnings, informational,
and even debug messages may be written over the Log API.
This change restructures a lot more pertaining to deployments, snapshots,
environments, and the like.
The most notable change is that the notion of a deploy.Source is introduced,
which splits the responsibility between the deploy.Plan -- which simply
understands how to compute and carry out deployment plans -- and the idea
of something that can produce new objects on-demand during deployment.
The primary such implementation is evalSource, which encapsulates an
interpreter and takes a package, args, and config map, and proceeds to run
the interpreter in a distinct goroutine. It synchronizes as needed to
poke and prod the interpreter along its path to create new resource objects.
There are two other sources, however. First, a nullSource, which simply
refuses to create new objects. This can be handy when writing isolated
tests but is also used to simulate the "empty" environment as necessary to
do a complete teardown of the target environment. Second, a fixedSource,
which takes a pre-computed array of objects, and hands those, in order, to
the planning engine; this is mostly useful as a testing technique.
Boatloads of code is now changed and updated in the various CLI commands.
This further chugs along towards pulumi/lumi#90. The end is in sight.
This change includes approximately 1/3rd of the change necessary
to support output properties, as per pulumi/lumi#90.
In short, the runtime now has a new hidden type, Latent<T>, which
represents a "speculative" value, whose eventual type will be T,
that we can use during evaluation in various ways. Namely,
operations against Latent<T>s generally produce new Latent<U>s.
During planning, any Latent<T>s that end up in resource properties
are transformed into "unknown" property values. An unknown property
value is legal only during planning-time activities, such as Check,
Name, and InspectChange. As a result, those RPC interfaces have
been updated to include lookaside maps indicating which properties
have unknown values. My intent is to add some helper functions to
make dealing with this circumstance more correct-by-construction.
For now, using an unresolved Latent<T> in a conditional will lead
to an error. See pulumi/lumi#67. Speculating beyond these -- by
supporting iterative planning and application -- is something we
want to support eventually, but it makes sense to do that as an
additive change beyond this initial support. That is a missing 1/3.
Finally, the other missing 1/3rd which will happen much sooner
than the rest is restructuing plan application so that it will
correctly observe resolution of Latent<T> values. Right now, the
evaluation happens in one single pass, prior to the application, and
so Latent<T>s never actually get witnessed in a resolved state.
