This encapsulates the logic for selecting an implied FQN for an
unqualified type name, which could either come from a local name used in
a module without specifying an explicit source for it or from the prefix
of a resource type on a resource that doesn't explicitly set "provider".
This replaces the previous behavior of just directly calling
NewDefaultProvider everywhere so that we can use a different implication
for the local name "terraform", to refer to the built-in terraform
provider rather than the stale one that's on registry.terraform.io for
compatibility with other Terraform versions.
We've been using the models from the "moduledeps" package to represent our
provider dependencies everywhere since the idea of provider dependencies
was introduced in Terraform 0.10, but that model is not convenient to use
for any use-case other than the "terraform providers" command that needs
individual-module-level detail.
To make things easier for new codepaths working with the new-style
provider installer, here we introduce a new model type
getproviders.Requirements which is based on the type the new installer was
already taking as its input. We have new methods in the states, configs,
and earlyconfig packages to produce values of this type, and a helper
to merge Requirements together so we can combine config-derived and
state-derived requirements together during installation.
The advantage of this new model over the moduledeps one is that all of
recursive module walking is done up front and we produce a simple, flat
structure that is more convenient for the main use-cases of selecting
providers for installation and then finding providers in the local cache
to use them for other operations.
This new model is _not_ suitable for implementing "terraform providers"
because it does not retain module-specific requirement details. Therefore
we will likely keep using moduledeps for "terraform providers" for now,
and then possibly at a later time consider specializing the moduledeps
logic for only what "terraform providers" needs, because it seems to be
the only use-case that needs to retain that level of detail.
* terraform: large refactor to use Provider from configs.Resource
configs.Resource.ImpliedProvider() now returns a string; it is the
callers' responsibility to turn that into an addrs.Provider if needed.
GraphNodeProviderConsumer ProvidedBy() no longer returns nil (reverting
to earlier, pre-provider-fqn behavior): it will return either the
provider set in config, provider set in state, or the default provider.
This function can already produce suitable diagnostic messages which we'd
like to preserve, but it cannot produce source location information, and
so we'll amend the diagnostics to include that on the way out while
retaining all of the other values in the diagnostics.
* configs: parse provider source string during module merge
This was the smallest unit of work needed to start writing provider
source tests!
* Update configs/parser_test.go
Co-Authored-By: Alisdair McDiarmid <alisdair@users.noreply.github.com>
Change ModuleInstance to Module in AbsProviderConfig, because providers
need to be handled before module expansion, and should not be used
defined inside an expanded module at all.
Renaming of the addrs type can happen later, when there's less work
in-flight around provider configuration.
* add Config to AttachSchemaTransformer for providerFqn lookup
* terraform: refactor ProvidedBy() to return nil when provider is not set
in config or state
Implement a new provider_meta block in the terraform block of modules, allowing provider-keyed metadata to be communicated from HCL to provider binaries.
Bundled in this change for minimal protocol version bumping is the addition of markdown support for attribute descriptions and the ability to indicate when an attribute is deprecated, so this information can be shown in the schema dump.
Co-authored-by: Paul Tyng <paul@paultyng.net>
The provider FQN is becoming our primary identifier for a provider, so
it's important that we are clear about the equality rules for these
addresses and what characters are valid within them.
We previously had a basic regex permitting ASCII letters and digits for
validation and no normalization at all. We need to do at least case
folding and UTF-8 normalization because these names will appear in file
and directory names in case-insensitive filesystems and in repository
names such as on GitHub.
Since we're already using DNS-style normalization and validation rules
for the hostname part, rather than defining an entirely new set of rules
here we'll just treat the provider namespace and type as if they were
single labels in a DNS name. Aside from some internal consistency, that
also works out nicely because systems like GitHub use organization and
repository names as part of hostnames (e.g. with GitHub Pages) and so
tend to apply comparable constraints themselves.
This introduces the possibility of names containing letters from alphabets
other than the latin alphabet, and for latin letters with diacritics.
That's consistent with our introduction of similar support for identifiers
in the language in Terraform 0.12, and is intended to be more friendly to
Terraform users throughout the world that might prefer to name their
products using a different alphabet. This is also a further justification
for using the DNS normalization rules: modern companies tend to choose
product names that make good domain names, and now such names will be
usable as Terraform provider names too.
Added configs.Module.ProviderForLocalProviderConfig which allows
terraform.ProviderTransformer to get the provider FQN from the module,
instead of assuming NewLegacyProvider.
a large refactor to addrs.AbsProviderConfig, embedding the addrs.Provider instead of a Type string. I've added and updated tests, added some Legacy functions to support older state formats and shims, and added a normalization step when reading v4 (current) state files (not the added tests under states/statefile/roundtrip which work with both current and legacy-style AbsProviderConfig strings).
The remaining 'fixme' and 'todo' comments are mostly going to be addressed in a subsequent PR and involve looking up a given local provider config's FQN. This is fine for now as we are only working with default assumption.
* configs: added map of ProviderLocalNames to configs.Module
We will need to lookup any user-supplied local names for a given FQN.
This PR adds a map of ProviderLocalNames to the Module, along with
adding tests for this and for decodeRequiredProvidersBlock.
This also introduces the appearance of support for a required_provider
"source" attribute, but ignores any user-supplied source and instead
continues to assume that addrs.NewLegacyProvider is the way to go.
This is a stepping-stone PR for the provider source project. In this PR
"legcay-stype" FQNs are created from the provider name string. Future
work involves encoding the FQN directly in the AbsProviderConfig and
removing the calls to addrs.NewLegacyProvider().
* Introduce "Local" terminology for non-absolute provider config addresses
In a future change AbsProviderConfig and LocalProviderConfig are going to
become two entirely distinct types, rather than Abs embedding Local as
written here. This naming change is in preparation for that subsequent
work, which will also include introducing a new "ProviderConfig" type
that is an interface that AbsProviderConfig and LocalProviderConfig both
implement.
This is intended to be largely just a naming change to get started, so
we can deal with all of the messy renaming. However, this did also require
a slight change in modeling where the Resource.DefaultProviderConfig
method has become Resource.DefaultProvider returning a Provider address
directly, because this method doesn't have enough information to construct
a true and accurate LocalProviderConfig -- it would need to refer to the
configuration to know what this module is calling the provider it has
selected.
In order to leave a trail to follow for subsequent work, all of the
changes here are intended to ensure that remaining work will become
obvious via compile-time errors when all of the following changes happen:
- The concept of "legacy" provider addresses is removed from the addrs
package, including removing addrs.NewLegacyProvider and
addrs.Provider.LegacyString.
- addrs.AbsProviderConfig stops having addrs.LocalProviderConfig embedded
in it and has an addrs.Provider and a string alias directly instead.
- The provider-schema-handling parts of Terraform core are updated to
work with addrs.Provider to identify providers, rather than legacy
strings.
In particular, there are still several codepaths here making legacy
provider address assumptions (in order to limit the scope of this change)
but I've made sure each one is doing something that relies on at least
one of the above changes not having been made yet.
* addrs: ProviderConfig interface
In a (very) few special situations in the main "terraform" package we need
to make runtime decisions about whether a provider config is absolute
or local.
We currently do that by exploiting the fact that AbsProviderConfig has
LocalProviderConfig nested inside of it and so in the local case we can
just ignore the wrapping AbsProviderConfig and use the embedded value.
In a future change we'll be moving away from that embedding and making
these two types distinct in order to represent that mapping between them
requires consulting a lookup table in the configuration, and so here we
introduce a new interface type ProviderConfig that can represent either
AbsProviderConfig or LocalProviderConfig decided dynamically at runtime.
This also includes the Config.ResolveAbsProviderAddr method that will
eventually be responsible for that local-to-absolute translation, so
that callers with access to the configuration can normalize to an
addrs.AbsProviderConfig given a non-nil addrs.ProviderConfig. That's
currently unused because existing callers are still relying on the
simplistic structural transform, but we'll switch them over in a later
commit.
* rename LocalType to LocalName
Co-authored-by: Kristin Laemmert <mildwonkey@users.noreply.github.com>
Renamed file.ProviderRequirements to file.RequiredProviders to match the
name of the block in the configuration. file.RequiredProviders contains
the contents of the file(s); module.ProviderRequirements contains the
parsed and merged provider requirements.
Extended decodeRequiredProvidersBlock to parse the new provider source
syntax (version only, it will ignore any other attributes).
Added some tests; swapped deep.Equal with cmp.Equal in the
terraform/module_dependencies_test.go because deep was not catching
incorrect constraints.
The existing "type" argument allows specifying a type constraint that
allows for some basic validation, but often there are more constraints on
a variable value than just its type.
This new feature (requiring an experiment opt-in for now, while we refine
it) allows specifying arbitrary validation rules for any variable which
can then cause custom error messages to be returned when a caller provides
an inappropriate value.
variable "example" {
validation {
condition = var.example != "nope"
error_message = "Example value must not be \"nope\"."
}
}
The core parts of this are designed to do as little new work as possible
when no validations are specified, and thus the main new checking codepath
here can therefore only run when the experiment is enabled in order to
permit having validations.
* deps: bump terraform-config-inspect library
* configs: parse `version` in new required_providers block
With the latest version of `terraform-config-inspect`, the
required_providers attribute can now be a string or an object with
attributes "source" and "version". This change allows parsing the
version constraint from the new object while ignoring any given source attribute.
In an earlier change we switched to defining our own sets of detectors,
getters, etc for go-getter in order to insulate us from upstream changes
to those sets that might otherwise change the user-visible behavior of
Terraform's module installer.
However, we apparently neglected to actually refer to our local set of
detectors, and continued to refer to the upstream set. Here we catch up
with the latest detectors from upstream (taken from the version of
go-getter we currently have vendored) and start using that fixed set.
Currently we are maintaining these custom go-getter sets in two places
due to the configload vs. initwd distinction. That was already true for
goGetterGetters and goGetterDecompressors, and so I've preserved that for
now just to keep this change relatively simple; in later change it would
be nice to factor these "get with go getter" functions out into a shared
location which we can call from both configload and initwd.
* configs: move ProviderConfigCompact[Str] from addrs to configs
The configs package is aware of provider name and type (which are the
same thing today, but expected to be two different things in a future
release), and should be the source of truth for a provider config
address. This is an intermediate step; the next step will change the returned types to something based in the configs package.
* command: rename choosePlugins to chooseProviders to clarify scope of function
* use `Provider.LegacyString()` (instead of `Provider.Type`) consistently
* explicitly create legacy-style provider (continuing from above change)
Traditionally we've preferred to release new language features in major
releases only, because we can then use the beta cycle to gather feedback
on the feature and learn about any usability challenges or other
situations we didn't consider during our design in time to make those
changes before inclusion in a stable release.
This "experiments" feature is intended to decouple the feedback cycle for
new features from the major release rhythm, and thus allow us to release
new features in minor releases by first releasing them as experimental for
a minor release or two, adjust for any feedback gathered during that
period, and then finally remove the experiment gate and enable the feature
for everyone.
The intended model here is that anything behind an experiment gate is
subject to breaking changes even in patch releases, and so any module
using these experimental features will be broken by a future Terraform
upgrade.
The behavior implemented here is:
- Recognize a new "experiments" setting in the "terraform" block which
allows module authors to explicitly opt in to experimental features.
terraform {
experiments = [resource_for_each]
}
- Generate a warning whenever loading a module that has experiments
enabled, to avoid accidentally depending on experimental features and
thus risking unexpected breakage on next Terraform upgrade.
- We check the enabled experiments against the configuration at module
load time, which means that experiments are scoped to a particular
module. Enabling an experiment in one module does not automatically
enable it in any other module.
This experiments mechanism is itself an experiment, and so I'd like to
use the resource for_each feature to trial it. Because any configuration
using experiments is subject to breaking changes, we are free to adjust
this experiments feature in future releases as we see fit, but once
for_each is shipped without an experiment gate we'll be blocked from
making significant changes to it until the next major release at least.
The configs package is aware of provider name and type (which are the
same thing today, but expected to be two different things in a future
release), and should be the source of truth for a provider config
address.
* huge change to weave new addrs.Provider into addrs.ProviderConfig
* terraform: do not include an empty string in the returned Providers /
Provisioners
- Fixed a minor bug where results included an extra empty string
* terraform/context: use new addrs.Provider as map key in provider factories
* added NewLegacyProviderType and LegacyString funcs to make it explicit that these are temporary placeholders
This PR introduces a new concept, provider fully-qualified name (FQN), encapsulated by the `addrs.Provider` struct.
Add deprecation warning for references from destroy provisioners or
their connections to external resources or values. In order to ensure
resource destruction can be completed correctly, destroy nodes must be
able to evaluate with only their instance state.
We have sufficient information to validate destroy-time provisioners
early on during the config loading process. Later on these can be
converted to hard errors, and only allow self, count.index, and each.key
in destroy provisioners. Limited the provisioner and block evaluation
scope later on is tricky, but if the references can never be loaded,
then they will never be encountered during evaluation.
`terraform 0.12upgrade` assumes that the configuration has passed 0.11
init, but did not explicitly check that the configuration was valid.
Certain issues would not get caught because the configuration was
syntactically valid. In this case, int or float values out of range
resulted in a panic from `Value()`.
Since running a 0.11 validate command is a breaking change, this PR
merely moves the `Value()` logic for ints and floats into `configupgrade` so
the error can be returned to the user, instead of causing a panic.
Following on from de652e22a26b, this introduces deprecation warnings for
when an attribute value expression is a template with only a single
interpolation sequence, and for variable type constraints given in quotes.
As with the previous commit, we allowed these deprecated forms with no
warning for a few releases after v0.12.0 to ensure that folks who need to
write cross-compatible modules for a while during upgrading would be able
to do so, but we're now marking these as explicitly deprecated to guide
users towards the new idiomatic forms.
The "terraform 0.12upgrade" tool would've already updated configurations
to not hit these warnings for those who had pre-existing configurations
written for Terraform 0.11.
The main target audience for these warnings are newcomers to Terraform who
are learning from existing examples already published in various spots on
the wider internet that may be showing older Terraform syntax, since those
folks will not be running their configurations through the upgrade tool.
These warnings will hopefully guide them towards modern Terraform usage
during their initial experimentation, and thus reduce the chances of
inadvertently adopting the less-readable legacy usage patterns in
greenfield projects.
Terraform 0.12.0 removed the need for putting references and keywords
in quotes, but we disabled the deprecation warnings for the initial
release in order to avoid creating noise for folks who were intentionally
attempting to maintain modules that were cross-compatible with both
Terraform 0.11 and Terraform 0.12.
However, with Terraform 0.12 now more widely used, the lack of these
warnings seems to be causing newcomers to copy the quoted versions from
existing examples on the internet, which is perpetuating the old and
confusing quoted form in newer configurations.
In preparation for phasing out these deprecated forms altogether in a
future major release, and for the shorter-term benefit of giving better
feedback to newcomers when they are learning from outdated examples, we'll
now re-enable those deprecation warnings, and be explicit that the old
forms are intended for removal in a future release.
In order to properly test this, we establish a new set of test
configurations that explicitly mark which warnings they are expecting and
verify that they do indeed produce those expected warnings. We also
verify that the "success" tests do _not_ produce warnings, while removing
the ones that were previously written to succeed but have their warnings
ignored.
During the 0.12 work we intended to move all of the variable value
collection logic into the UI layer (command package and backend packages)
and present them all together as a unified data structure to Terraform
Core. However, we didn't quite succeed because the interactive prompts
for unset required variables were still being handled _after_ calling
into Terraform Core.
Here we complete that earlier work by moving the interactive prompts for
variables out into the UI layer too, thus allowing us to handle final
validation of the variables all together in one place and do so in the UI
layer where we have the most context still available about where all of
these values are coming from.
This allows us to fix a problem where previously disabling input with
-input=false on the command line could cause Terraform Core to receive an
incomplete set of variable values, and fail with a bad error message.
As a consequence of this refactoring, the scope of terraform.Context.Input
is now reduced to only gathering provider configuration arguments. Ideally
that too would move into the UI layer somehow in a future commit, but
that's a problem for another day.
Previously we were using the experimental HCL 2 repository, but now we'll
shift over to the v2 import path within the main HCL repository as part of
actually releasing HCL 2.0 as stable.
This is a mechanical search/replace to the new import paths. It also
switches to the v2.0.0 release of HCL, which includes some new code that
Terraform didn't previously have but should not change any behavior that
matters for Terraform's purposes.
For the moment the experimental HCL2 repository is still an indirect
dependency via terraform-config-inspect, so it remains in our go.sum and
vendor directories for the moment. Because terraform-config-inspect uses
a much smaller subset of the HCL2 functionality, this does still manage
to prune the vendor directory a little. A subsequent release of
terraform-config-inspect should allow us to completely remove that old
repository in a future commit.
copyDir is used in configload/getter.go to copy previously downloaded modules instead of using the go-getter client every time. The go-getter client downloads dotfiles, but copyDir did not copy dotfiles, leading to inconsistent behaviour when reusing the same module source.
In order to allow lazy evaluation of resource indexes, we can't index
resources immediately via GetResourceInstance. Change the evaluation to
always return whole Resources via GetResource, and index individual
instances during expression evaluation.
This will allow us to always check for invalid index errors rather than
returning an unknown value and ignoring it during apply.
We can only validate MinItems >= 1 (equiv to "Required") during
decoding, as dynamic blocks each only decode as a single block. MaxItems
cannot be validated at all, also because of dynamic blocks, which may
have any number of blocks in the config.
Due to both the nature of dynamic blocks, and the need for resources to
sometimes communicate incomplete values, we cannot validate MinItems and
MaxItems in CoerceValue.
A provider may not have the data to fill in required block values in all
cases during the resource Read operation. This is more common in import,
because there is no initial configuration or state, and it's possible
some values are only provided in the configuration.
The original intent of MinItems and MaxItems in the schema was to
enforce configuration constraints, not to enforce what the resource
could save in the state. Since the configuration is already statically
validated, and the Schema is validated against the configuration in a
separate step, we can drop these extra validation constraints in
CoerceValue and relax it to only ensure the types conform to what is
expected.
If a block was defined via "dynamic", there will be only one block value
until the expansion is known. Since we can't detect dynamic blocks at
this point, don't verify MinItems while there are unknown values in the
config.
The decoder spec can also only check for existence of a block, so limit
the check to 0 or 1.
This also fixes a few things with resource for_each:
It makes validation more like validation for count.
It makes sure the index is stored in the state properly.
In some cases (see #22020 for a specific example), the parsed hilNode
can be nil. This causes a series of panics. Instead, return an error and
move on.
When loading nested modules, the child module diagnostics were dropped
in the recursive function. This mean that the config from the submodules
wasn't fully loaded, even though no errors were reported to the user.
This caused further problems if the plan was stored in a plan file, when
means only the partial configuration was stored for the subsequent apply
operation, which would result in unexplained "Resource node has no
configuration attached" errors later on.
Also due to the child module diagnostics being lost, any newly added
nested modules would be silently ignored until `init` was run again
manually.
Previously, adding a version constraint to a module that was previously
recorded without a version in the module manifest would cause a panic.
Instead, we now use a slight variant of the "dependencies have changed"
error that doesn't try to print out a specific version number.
Previously we were trying to access a field of the analysis object before
checking if analysis produced errors. The analysis function usually
returns a nil analysis on error, so this would result in a panic whenever
that happened.
Now we'll dereference the analysis object pointer only after checking for
errors, so we'll get a chance to report the analysis error to the user.
The expression upgrade functionality mostly ignores comments because in
the old language the syntax prevented comments from appearing in the
middle of expressions, but there was one exception: object expressions.
Because HCL 1 used ObjectType both for blocks and for object expressions,
that is the one situation where something we consider to be an expression
could have inline attached comments in the old language.
We migrate these here so we don't lose these comments that don't appear
anywhere else. Other comments get gathered up into a general comments
set maintained inside the analysis object and so will be printed out as
required _between_ expressions, just as they did before.
Previously we were treating "dynamic" blocks in configuration the same as
any other block type when merging config bodies, so that dynamic blocks
in the override would override any dynamic blocks present in the base,
without considering the dynamic block type.
It's more useful and intuitive for us to treat dynamic blocks as if they
are instances of their given block type for the purpose of overriding.
That means a foo block can be overridden by a dynamic "foo" block and
vice-versa, and dynamic blocks of different types do not interact at all
during overriding.
This requires us to recognize dynamic blocks and treat them specially
during decoding of a merged body. We leave them unexpanded here because
this package is not responsible for dynamic block expansion (that happens
in the sibling "lang" package) but we do decode them enough to recognize
their labels so we can treat them as if they were blocks of the labelled
type.
In study of existing providers we've found a pattern we werent previously
accounting for of using a nested block type to represent a group of
arguments that relate to a particular feature that is always enabled but
where it improves configuration readability to group all of its settings
together in a nested block.
The existing NestingSingle was not a good fit for this because it is
designed under the assumption that the presence or absence of the block
has some significance in enabling or disabling the relevant feature, and
so for these always-active cases we'd generate a misleading plan where
the settings for the feature appear totally absent, rather than showing
the default values that will be selected.
NestingGroup is, therefore, a slight variation of NestingSingle where
presence vs. absence of the block is not distinguishable (it's never null)
and instead its contents are treated as unset when the block is absent.
This then in turn causes any default values associated with the nested
arguments to be honored and displayed in the plan whenever the block is
not explicitly configured.
The current SDK cannot activate this mode, but that's okay because its
"legacy type system" opt-out flag allows it to force a block to be
processed in this way anyway. We're adding this now so that we can
introduce the feature in a future SDK without causing a breaking change
to the protocol, since the set of possible block nesting modes is not
extensible.
These helpers determine the value that would be used for a particular
schema construct if the configuration construct it represents is not
present (or, in the case of *Block, empty) in the configuration.
This is different than cty.NullVal on the implied type because it might
return non-null "empty" values for certain constructs if their absence
would be reported as such during a decode with no required attributes or
blocks.
The v0.12 language supports numeric constants only in decimal notation, as
a simplification. For rare situations where a different base is more
appropriate, such as unix-style file modes, we've found it better for
providers to accept a string containing a representation in the
appropriate base, since that way the interpretation can be validated and
it will be displayed in the same way in the rendered plan diff, in
outputs, etc.
We use tv.Value() here to mimick how HCL 1 itself would have interpreted
these, and then format them back out in the canonical form, which
implicitly converts any non-decimal constants to decimal on the way
through.
In order to preserve pre-v0.12 idiom for list-of-object attributes, we'll
prefer to use block syntax for them except for the special situation where
the user explicitly assigns an empty list, where attribute syntax is
required in order to allow existing provider logic to differentiate from
an implicit lack of blocks.
* configs/configupgrade: detect invalid resource names and print a TODO
message
In terraform 0.11 and prior it was possible to start a resource name
with a number. This is no longer valid, as the resource name would would
be ambiguous with number values in HCL expressions.
Fixes#19919
* Update configs/configupgrade/test-fixtures/valid/invalid-resource-name/want/resource.tf
Co-Authored-By: mildwonkey <mildwonkey@users.noreply.github.com>
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.
* 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.
configs/configload and internal/initwd both had a copyDir function that
would fail if the source directory contained a symlinked directory,
because the os.FileMode.IsDir() returns false for symlinks.
This PR adds a check for a symlink and copies that symlink in the
target directory. It handles symlinks for both files and directories
(with included tests).
Fixes#20539
Terraform 0.11 and prior had an odd special case where a resource
attribute access for "count" would be resolved as the count for the
whole resource, rather than as an attribute of an individual instance as
for all other attributes.
Because Terraform 0.12 makes test_instance.foo appear as a list when count
is set (so it can be used in other expressions), it's no longer possible
to have an attribute in that position: lists don't have attributes.
Fortunately we don't really need that special case anymore since it
doesn't do anything we can't now do with the length(...) function.
This upgrade rule, then, detects references like test_instance.foo.count
and rewrites to length(test_instance.foo). As a special case, if
test_instance.foo doesn't have "count" set then it just rewrites as the
constant 1, which mimics what would've happened in that case in Terraform
0.11.
Prior to Terraform v0.12 it was possible for a provider to secretly set
some default arguments for the "connection" block, which most commonly
included a hard-coded type of "ssh" and a value from "host".
In the interests of "explicit is better than implicit", Terraform 0.12 no
longer has this feature and instead requires connection settings to be
written explicitly in terms of the resource's exported attributes. For
compatibility though, the upgrade tool will insert expressions that are
as close as possible to the logic the provider formerly implemented, or
in a few rare cases a TF-UPGRADE-TODO comment to fix it up manually.
Some of the existing resource type implementations have incredibly
complicated implementations of selecting a single host IP address to use
and don't expose the result of that as an attribute, so for now we handle
those via a complicated Terraform language expression achieving the same
result. Ideally these providers would introduce a new attribute that
exports the same address formerly exported as the hostname before their
initial v0.12-compatible release, in which case we can simplify these to
just reference the attribute in question. That would be preferable also
because it would allow use of that exported attribute in other contexts,
such as in a null_resource provisioner somewhere else or in an output
to allow a caller to deal with the SSH part itself.
This uses the fixed "superset" schema from the main terraform package to
apply our standard expression mapping, with the exception of "type" where
interpolation sequences are not supported due to the type being evaluated
early to retrieve the schema for decoding the rest.
Aside from the two special meta-arguments "connection" and "provisioner"
this is just our standard mapping from schema to conversion rules, using
the provisioner's configuration schema.
Martin Atkins