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.
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.
