We previously stubbed most of this out because it hadn't yet been updated
to support the new state types, etc.

This restores all of the previous behavior as covered by the tests.

We intentionally remove one behavior that was not covered by the tests:
we used to allow retrieval of outputs from non-root modules using the
-module option, but since we no longer persist non-root outputs in the
state we can no longer support this without a full expression evaluation
walk, and that'd be overkill for this otherwise-simple command. Descendant
module outputs are not part of the public interface of a configuration
anyway, so accessing them from outside in this way is an anti-pattern.

(For debugging scenarios it is still possible to access these from
"terraform console", which _does_ do a full evaluation graph walk to
prepare its evaluation scope.)

The plan file writer requires a backend config to be present, but we don't
really need one for the sake of _this_ test, since we don't activate the
backend to render a plan graph, and so we just write in a placeholder.

Some underlying assumptions have shifted here, so although the behavior
is still broadly the same we need to accommodate some different details.

This fixes TestConsole_tfvars.

This connects a missing link left by earlier refactoring: the command
package is responsible for gathering up variable values provided by the
user and passing them through to the backend to use in operations.

There are several steps here and a number of them can include reaching out
to remote servers or executing local processes, so it's helpful to have
some trace logs to better narrow down causes of errors and hangs during
this step.

Our serialization of the backend configuration has changed slightly for
Terraform 0.12 due to reimplementing it in terms of the HCL2 types, so
the base case that should be unchanged during the test needs to be
changed.

In all real cases the schemas should be populated here, but we don't want
to panic in UI rendering code if there's a bug here.

This can also be tripped up by tests with incomplete mocks. It's
unfortunate that this can therefore mask some problems in tests, but tests
can protect against it by asserting on specific output text rather than
just assuming that a zero exit status is a pass.

In earlier refactoring we skipped implementing prior state safety checks,
propagating the target addresses from plan, and verifying that all of
the providers are exactly the same from the plan being created.

This change reinstates those checks, including a new error message for
the "stale plan" situation.

also run go mod tidy

If we fail to parse the resource address given to "terraform import" then
it's helpful to produce a "source code" snippet of what the user provided
so they might see more precisely which part of the address was invalid.

Most of this is just updates to allow for the fact that we now always save
the provider address as part of resource state, whereas before it was only
saved conditionally.

This also updates TestTaint_module for the intentional change that it now
expects a child module to be specified using normal resource address
syntax, rather than as a separate -module option.

The untaint command now uses normal resource address syntax to specify the
module path, rather than passing it in as a separate argument.

Resource instance state now always includes the provider address fo each
resource, so our expected state output strings needed to be adjusted.

This is just to make sure they show up later when we are working on the
tests, so we can be sure not to forget to address them.

Added a very simple test with state and schema.
TODO: if tests are added we should test using golden files (and example
state files, instead of strings). This seemed unnecessary with the
simple test cases.

Use functions from format/diff to print values

format/state now requires provider schemas to properly format output
state. command/show has been modified to pass a context to format.State.

In previous work we didn't quite connect these dots. The connection here
is sub-awesome since the existing interfaces here had some unfortunate
assumptions that we'd like to move away from (like the idea of a "nil
backend" implying the local backend) but we're accepting this for now to
avoid another big round of refactoring.

The main implication of this is that we will now always include a backend
configuration in the plan, though it might just be a placeholder config
for the local backend in the remaining cases where that's still implicitly
set. Later we will change this so that there is no implicit local backend
at all (terraform init is always required, _it_ will deal with setting
implicitly setting the local backend when appropriate), which will allow
us to rework this to be more straightforward and less "spooky".

If we don't do this, we can't produce any output when applying a saved
plan file.

Here we also introduce a check to the local backend's ReportResult
function so that it won't panic if CLI init is skipped, although that
will no longer happen in the apply-from-file case due to the change
described in the previous paragraph.

We can't generate a valid plan file without a backend configuration to
write into it, but it's the responsibility of the caller (the command
package) to manage the backend configuration mechanism, so we require it
to tell us what to write here.

This feels a little strange because the backend in principle knows its
own config, but in practice the backend only knows the _processed_ version
of the config, not the raw configuration value that was used to configure
it.

converted the existing testPlanState() from terraform.State to
states.State to fix various plan tests.

reverted the "bandaid" in plans/planfile/tfplan.go - at this moment the
backend tests do not include backend configuration, and so the planfile
package can write the plan file but not read it back in. That will be
revisted in a separate track of work.

I have no confidence in the change to plans/planfile/tfplan.go. The
tests were passing an empty backend config, which planfile  was able to
write to a file but not read from the same file. This change let me move
past that and it did not break any tests in the planfile package, but I
am concerned that it introduces undesired behavior.

for TestLocal_applyBackendFail, config is relative to the tests' wd

The legacy test wasn't really testing anything useful, just the plan
behavior with no diff in a module returned a module with no diff.
There's no reason to convert this to the new plans, since there's no
legacy behavior to match.