We expect that in order to continue to evolve the language without
breaking existing modules we will at some point need to have a way to mark
when a particular module is expecting a newer interpretation of the
language.
Although it's too early to do any deep preparation for that, this commit
aims to proactively reserve an argument named "language" inside
"terraform" blocks, which currently only accepts the keyword TF2021 that
is intended to represent "the edition of the Terraform language as defined
in 2021".
That argument also defaults to TF2021 if not set, so in practice there's
no real reason to set this today, but this minimal validation today is
intended to give better feedback to users of older Terraform versions in
the event that we introduce a new language edition later and they try to
use an module incompatible with their Terraform version.
We now permit at most one `required_providers` block per module (except
for overrides). This prevents users (and Terraform) from struggling to
understand how to merge multiple `required_providers` configurations,
with `version` and `source` attributes split across multiple blocks.
Because only one `required_providers` block is permitted, there is no
need to concatenate version constraints and resolve them. This allows us
to simplify the structs used to represent provider requirements,
aligning more closely with other structs in this package.
This commit also fixes a semantic use-before-initialize bug, where
resources defined before a `required_providers` block would be unable to
use its source attribute. We achieve this by processing the module's
`required_providers` configuration (and overrides) before resources.
Overrides for `required_providers` work as before, replacing the entire
block per provider.
With provider dependencies now appearing inside a nested block, it seems
likely that configuration examples showing dependencies out of context
will sometimes mislead users into thinking that required_providers is
toplevel.
To give better feedback in that situation, we'll produce a specialized
error in that case hinting the correct structure to the user.
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>
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.
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.
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.
Previously we just ported over the simple "string", "list", and "map" type
hint keywords from the old loader, which exist primarily as hints to the
CLI for whether to treat -var=... arguments and environment variables as
literal strings or as HCL expressions.
However, we've been requested before to allow more specific constraints
here because it's generally better UX for a type error to be detected
within an expression in a calling "module" block rather than at some point
deep inside a third-party module.
To allow for more specific constraints, here we use the type constraint
expression syntax defined as an extension within HCL, which uses the
variable and function call syntaxes to represent types rather than values,
like this:
- string
- number
- bool
- list(string)
- list(any)
- list(map(string))
- object({id=string,name=string})
In native HCL syntax this looks like:
variable "foo" {
type = map(string)
}
In JSON, this looks like:
{
"variable": {
"foo": {
"type": "map(string)"
}
}
}
The selection of literal processing or HCL parsing of CLI-set values is
now explicit in the model and separate from the type, though it's still
derived from the type constraint and thus not directly controllable in
configuration.
Since this syntax is more complex than the keywords that replaced it, for
now the simpler keywords are still supported and "list" and "map" are
interpreted as list(any) and map(any) respectively, mimicking how they
were interpreted by Terraform 0.11 and earlier. For the time being our
documentation should continue to recommend these shorthand versions until
we gain more experience with the more-specific type constraints; most
users should just make use of the additional primitive type constraints
this enables: bool and number.
As a result of these more-complete type constraints, we can now type-check
the default value at config load time, which has the nice side-effect of
allowing us to produce a tailored error message if an override file
produces an invalid situation; previously the result was rather confusing
because the error message referred to the original definition of the
variable and not the overridden parts.
Some of the fields in our config structs are either mandatory in primary
files or there is a default value that we apply if absent.
Unfortunately override files impose the additional constraint that we
be allowed to omit required fields (which have presumably already been
set in the primary files) and that we are able to distinguish between a
default value and omitting a value entirely.
Since most of our fields were already acceptable for override files, here
we just add some new fields to deal with the few cases where special
handling is required and a helper function to disable the "Required" flag
on attributes in a given schema.
This is a first pass of decoding of the main Terraform configuration file
format. It hasn't yet been tested with any real-world configurations, so
it will need to be revised further as we test it more thoroughly.
Martin Atkins