Previously we used the word "Environment" as the term for a deployment
target, but since then we've started to use the term Stack. Adopt this
across the CLI.
From a user's point of view, there are a few changes:
1. The `env` verb has been renamed to `stack`
2. The `-e` and `--env` options to commands which operate on an
environment now take `-s` or `--stack` instead.
3. Becase of (2), the commands that used `-s` to display a summary now
only support passing the full option name (`--summary`).
On the local file system, we still store checkpoint data in the `env`
sub-folder under `.pulumi` (so we can reuse existing checkpoint files
that were written to the old folder)
Previously, the engine would write to io.Writer's to display output.
When hosted in `pulumi` these writers were tied to os.Stdout and
os.Stderr, but other applications hosting the engine could send them
other places (e.g. a log to be sent to an another application later).
While much better than just using the ambient streams, this was still
not the best. It would be ideal if the engine could just emit strongly
typed events and whatever is hosting the engine could care about
displaying them.
As a first step down that road, we move to a model where operations on
the engine now take a `chan engine.Event` and during the course of the
operation, events are written to this channel. It is the
responsibility of the caller of the method to read from the channel
until it is closed (singifying that the operation is complete).
The events we do emit are still intermingle presentation with data,
which is unfortunate, but can be improved over time. Most of the
events today are just colorized in the client and printed to stdout or
stderr without much thought.
Previously, you could pass an explicit path to a Pulumi program when
running preview or update and the tool would use that program when
planning or deploying, but continue to write state in the cwd. While
being able to operate on a specific package without having to cd'd all
over over the place is nice, this specific implemntation was a little
scary because it made it easier to run two different programs with the
same local state (e.g config and checkpoints) which would lead to
surprising results.
Let's move to a model that some tools have where you can pass a
working directory and the tool chdir's to that directory before
running. This way any local state that is stored will be stored
relative to the package we are operating on instead of whatever the
current working directory is.
Fixes#398
Previously, the engine was concered with maintaing information about
the currently active environment. Now, the CLI is in charge of
this. As part of this change, the engine can now assume that every
environment has a non empty name (and I've added asserts on the
entrypoints of the engine API to ensure that any consumer of the
engine passes a non empty environment name)
