The current way to refer to a managed resource is to use its resource type
name as a top-level symbol in the reference. This is convenient and makes
sense given that managed resources are the primary kind of object in
Terraform.
However, it does mean that an externally-extensible namespace (the set
of all possible resource type names) overlaps with a reserved word
namespace (the special prefixes like "path", "var", etc), and thus
introducing any new reserved prefix in future risks masking an existing
resource type so it can't be used anymore.
We only intend to introduce new reserved symbols as part of future
language editions that each module can opt into separately, and when doing
so we will always research to try to choose a name that doesn't overlap
with commonly-used providers, but not all providers are visible to us and
so there is always a small chance that the name we choose will already be
in use by a third-party provider.
In preparation for that event, this introduces an alternative way to refer
to managed resources that mimics the reference style used for data
resources: resource.type.name . When using this form, the second portion
is _always_ a resource type name and never a reserved word.
There is currently no need to use this because all of the already-reserved
symbol names are effectively blocked from use by existing Terraform
versions that lack this escape hatch. Therefore there's no explicit
documentation about it yet.
The intended use for this is that a module upgrade tool for a future
language edition would detect references to resource types that have now
become reserved words and add the "resource." prefix to keep that
functionality working. Existing modules that aren't opted in to the new
language edition would keep working without that prefix, thus keeping to
compatibility promises.
Our diagnostics model allows for optionally annotating an error or warning
with information about the expression and eval context it was generated
from, which the diagnostic renderer for the UI will then use to give the
user some additional hints about what values may have contributed to the
error.
We previously didn't have those annotations on the results of evaluating
for_each expressions though, because in that case we were using the helper
function to evaluate an expression in one shot and thus we didn't ever
have a reference to the EvalContext in order to include it in the
diagnostic values.
Now, at the expense of having to handle the evaluation at a slightly lower
level of abstraction, we'll annotate all of the for_each error messages
with source expression information. This is valuable because we see users
often confused as to how their complex for_each expressions ended up being
invalid, and hopefully giving some information about what the inputs were
will allow more users to self-solve.
In order to properly evaluate a destroy provisioner, we cannot rely on
the usual evaluation context, because the resource has already been
removed from the state.
EvalSelfBlock evaluates an hcl.Body in the limited scope of a single
object as "self", with the added values of "count.index" and "each.key".
There is no codepath that can use this any longer, since we need to
evaluate the modules as whole objects.
This means we're going to have to live for now with invalid module
output references returning "object" errors rather that "module".
In order to be able to use module values, and handle operations like
possibly invalid module indexes in conditional statements, whole modules
must always be returned during evaluation.
The fallback type for GetResource from an EachMap is a cty.Object,
because resource schemas may contain dynamically typed attributes.
Check for an Object type in the evaluation of self, to use the proper
GetAttr method when extracting the value.
self references do not need to be added to `managedResource`, and in
fact that could cause issues later if self is allowed in contexts other
than managed resources.
Coalesce 2 cases in the Referenceable switch, be take the
ContainingResource address of an instance beforehand.
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.
Continue only evaluating resource at a whole and push the indexing of
the resource down into the expression evaluation.
The exception here is that `self` must be an instance which must be
extracted from the resource. We now also add the entire resource to the
context, which was previously only partially populated with the self
referenced instance.
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.
Previously it was calling directly to hcldec.Variables, and thus missing
the special fixups we do inside ReferencesInBlock to deal with
Terraform-specific concerns such as our attribute-as-blocks preprocessing.
For any block content we evaluate dynamically via this API, we'll make a
special allowance for users to optionally write members of a list
attribute instead as a sequence of nested blocks, thus allowing some
existing provider features that were assuming this capability to continue
to support it after v0.12.
This should not be used for any new provider features, and should ideally
be eventually phased out so that there aren't two
similar-but-slightly-different syntaxes for saying the same thing.
This includes improved functionality for HCL's "dynamic block extension",
which will allow us (in a subsequent commit) to properly detect
dependencies inside nested "dynamic" blocks, where currently they get
missed.
For this commit though, we just upgrade HCL to a version that includes it
and make a small change to our "lang" package to align with an upstream
renaming.
Both depends_on and ignore_changes contain references to objects that we
can validate.
Historically Terraform has not validated these, instead just ignoring
references to non-existent objects. Since there is no reason to refer to
something that doesn't exist, we'll now verify this and return errors so
that users get explicit feedback on any typos they may have made, rather
than just wondering why what they added seems to have no effect.
This is particularly important for ignore_changes because users have
historically used strange values here to try to exploit the fact that
Terraform was resolving ignore_changes against a flatmap. This will give
them explicit feedback for any odd constructs that the configuration
upgrade tool doesn't know how to detect and fix.
This actually seems to be a bug in the underlying cty Convert function
since converting to cty.DynamicPseudoType should always just return the
input verbatim, but it seems like it's actually converting unknown values
of any type to be cty.DynamicVal, losing the type information.
We should eventually fix this in cty too, but having this extra check in
the Terraform layer is harmless and allows us to make progress without
context-switching.
In the initial move to HCL2 we started relying only on full expression
evaluation to catch attribute errors, but that's not sufficient for
resource attributes in practice because during validation we can't know
yet whether a resource reference evaluates to a single object or to a
list of objects (if count is set).
To address this, here we reinstate some static validation of resource
references by analyzing directly the reference objects, disregarding any
instance index if present, and produce errors if the remaining subsequent
traversal steps do not correspond to items within the resource type
schema.
This also allows us to produce some more specialized error messages for
certain situations. In particular, we can recognize a reference like
aws_instance.foo.count, which in 0.11 and prior was a weird special case
for determining the count value of a resource block, and offer a helpful
error showing the new length(aws_instance.foo) usage pattern.
This eventually delegates to the static traversal validation logic that
was added to the configschema package in a previous commit, which also
includes some specialized error messages that distinguish between
attributes and block types in the schema so that the errors relate more
directly to constructs the user can see in the configuration.
In future we could potentially move more of the checks from the dynamic
schema construction step to the static validation step, but resources
are the reference type that most needs this immediately due to the
ambiguity caused by the instance indexing syntax. We can safely refactor
other reference types to be statically validated in later releases.
This is verified by two pre-existing context validate tests which we
temporarily disabled during earlier work (now re-enabled) and also by a
new validate test aimed specifically at the special case for the "count"
attribute.
The "config" package is no longer used and will be removed as part
of the 0.12 release cleanup. Since configschema is part of the
"new world" of configuration modelling, it makes more sense for
it to live as a subdirectory of the newer "configs" package.
Due to how deeply the configuration types go into Terraform Core, there
isn't a great way to switch out to HCL2 gradually. As a consequence, this
huge commit gets us from the old state to a _compilable_ new state, but
does not yet attempt to fix any tests and has a number of known missing
parts and bugs. We will continue to iterate on this in forthcoming
commits, heading back towards passing tests and making Terraform
fully-functional again.
The three main goals here are:
- Use the configuration models from the "configs" package instead of the
older models in the "config" package, which is now deprecated and
preserved only to help us write our migration tool.
- Do expression inspection and evaluation using the functionality of the
new "lang" package, instead of the Interpolator type and related
functionality in the main "terraform" package.
- Represent addresses of various objects using types in the addrs package,
rather than hand-constructed strings. This is not critical to support
the above, but was a big help during the implementation of these other
points since it made it much more explicit what kind of address is
expected in each context.
Since our new packages are built to accommodate some future planned
features that are not yet implemented (e.g. the "for_each" argument on
resources, "count"/"for_each" on modules), and since there's still a fair
amount of functionality still using old-style APIs, there is a moderate
amount of shimming here to connect new assumptions with old, hopefully in
a way that makes it easier to find and eliminate these shims later.
I apologize in advance to the person who inevitably just found this huge
commit while spelunking through the commit history.
Whereas package "configs" deals with the static structure of the
configuration language, this new package "lang" deals with the dynamic
aspects such as expression evaluation.
So far this mainly consists of populating a hcl.EvalContext that contains
the values necessary to evaluate a block or an expression. There is also
special handling here for dynamic block generation using the HCL
"dynblock" extension, which is exposed in the public interface (rather
than hiding it as an implementation detail of EvalBlock) so that the
caller can then extract proper source locations for any result values
using the expanded body.
This also includes the beginnings of a replacement for the function table
handling that currently lives in the old "config" package, but most of
the functions are not yet ported and so this will expand in subsequent
commits.
Martin Atkins