This is an SDK version suitable for Terraform v0.12.0-beta2 and,
if no other important fixes land in the mean time, v0.12.0 final.

We have released the v0.12-oriented content to the website early in order
to support the beta process, but in some places we neglected to explicitly
mark features or content as being v0.12-only.

Here we add explicit markers to the main cases we've seen where readers
have reported confusion, along with some other tweaks in similar vein.

plugin/discovery: Parse warnings from TF Registry

Terraform Registry (and other registry implementations) can now return
an array of warnings with the versions response. These warnings are now
displayed to the user during a `terraform init`.

Allows us to surface warnings to the user using the tfdiags interfaces.

In earlier refactoring we updated these commands to support the new
address and state types, but attempted to partially retain the old-style
"StateFilter" abstraction that originally lived in the Terraform package,
even though that was no longer being used for any other functionality.

Unfortunately the adaptation of the existing filtering to the new types
wasn't exact and so these commands ended up having a few bugs that were
not covered by the existing tests.

Since the old StateFilter behavior was the source of various misbehavior
anyway, here it's removed altogether and replaced with some simpler
functions in the state_meta.go file that are tailored to the use-cases of
these sub-commands.

As well as just generally behaving more consistently with the other
parts of Terraform that use the new resource address types, this commit
fixes the following bugs:

- A resource address of aws_instance.foo would previously match an
  resource of ...

Our post-refresh safety check had the constraint and real type inverted,
so previously any refresh of a resource type with a dynamically-typed
attribute would fail this type check.

Also includes a small tweak to the error message from this check since the
old one was a little awkward to read in practice when the error is a
cty.PathError rendered with an attribute path prefix.

We were using the wrong cty operation to access map members, causing a
panic whenever a prior value was present for a resource type with a nested
block backed by a map value.

This includes two upstream fixes:

- Handle explicit JSON "null" consistently during decode of JSON syntax.
- Properly detect the end of a "heredoc" when formatting to avoid messing
  up indentation of other lines following the heredoc.

bump go version to 1.12

Terraform is way bigger than the core CLI tools and the language
now, and the docs have grown accordingly. So we're adding a
global index page to help users get around the many sections of the
docs site, and bumping the CLI/core docs down so they're no longer at the
top of the hierarchy.

The "right" (as in, conceptually pure) way to do this would be to actually
create a new level of directory hierarchy in between. But that would be real
expensive and annoying — the amount of 301s and links to edit would be
monumental, and it wouldn't gain us much beyond a certain picture-straightening
satisfaction, so I'm resisting the temptation.

The previous commit added a new flag to schema.Schema which is documented
to make a list with MaxItems: 1 be presented to Terraform Core as a single
value instead, giving a way to switch to non-list nested resources without
it being a breaking change for Terraform v0.11 users as long as it's done
prior to a provider's first v0.12-compatible release.

This is the implementation of that mechanism. It's intentionally
implemented as a suite of extra fixups rather than direct modifications to
existing shim code because we want to ensure that this has no effect
whatsoever on the result of a resource type that _isn't_ using AsSingle.

Although there is some small unit test coverage of the fixup steps here,
the primary testing for this is in the test provider since the integration
of all of these fixup steps in the correct order is the more important
result than any of the intermediate fixup steps.

This setting indicates that an attribute defined as TypeList or TypeSet
should be presented to Terraform Core as a single value instead when
running in Terraform v0.12 or later. It has no effect for Terraform v0.10
or v0.11.

This commit just introduces the setting without any associated behavior,
so it can be included in both the v0.12 and v0.11 branches. A subsequent
commit only to the v0.12 branch will introduce the behavior as part of
the protocol version 5 shims.

* command/providers schemas: return empty json object if config parses successfully but no providers found
* command/show (state): return an empty object if state is nil

don't try to treat "null" as json in diff output

Trying to decode and write "null" as json will panic, since it decodes
to nil.

Fixes #20653 

config: Mention other file hashing functions when file() detects unsupported contents

...well, I was ALMOST right in the previous commit.

As part of this, I'm copying the entire text of the 0.12
docs/configuration/modules.html page into docs/configuration-0-11/modules.html —
some of the 0.11 pages needed to be able to link to the moved content, I
didn't want to jump versions jarringly, and a close reading didn't reveal
anything in there that's inaccurate for 0.11.

This relies on a commit in the terraform-website repo, and should make updating
that list much less annoying.

ReadResource normalization

The changed value for the set attribute should be correctly read from
the provider.

This will allow resources to return an unexpected change to set blocks
and attributes, otherwise we could mask these changes during
normalization.

Change the "plan" argument in normalizeNullValues to "preferDst" to more
accurately describe what the option is doing, since it no longer applies
only to PlanResourceChange.

[Website] New Community Providers

* configs/configupgrade: detect possible relative module sources

If a module source appears to be a relative local path but does not have
a preceding ./, print a #TODO message for the user.

* internal/initwd: limit go-getter detectors to those supported by terraform
* internal/initwd: move isMaybeRelativeLocalPath check into getWithGoGetter

To avoid making two calls to getter.Detect, which potentially makes
non-trivial API calls, the "isMaybeRelativeLocalPath" check was moved to
a later step and a custom error type was added so user-friendly
diagnostics could be displayed in the event that a possible relative local
path was detected.

docs: Differentiate 0.11/0.12 in terraform_remote_state