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.
HCL diagnostics relating to expression evaluation include these, so this
is really just to pass that information through our Terraform-specific
diagnostics interface.
HCL will be the most frequent origin of a source range, so this helper
should make it easier to translate these between the two worlds so we
can more easily use them in native Terraform diagnostics and other
messaging.
Currently we lean heavily on the Go error type as our primary means of
describing errors, and along with that use several more specialized
implementations of it in different spots for additional capabilities such
as multiple errors in one object, source code range references, etc.
We also have a rather ad-hoc approach of returning an array of warnings
from certain functions along with one or multiple errors.
This rather-disorganized approach makes it hard for us to present
user-facing error messages consistently. As a step towards mitigating
this, package tfdiags provides a model for user-facing error and warning
messages and helper functions for creating them from various other
error and warning types used elsewhere in Terraform.
This mechanism is intended to be used to report errors and warnings where
the audience is the Terraform user, and so it may go a few layers deep
down the call stack into codepaths like config parsing, interpolation, etc
but is primarily a UX concern. The deepest reaches of Terraform core will
continue using "error" as normal, with higher layers preparing error
messages for presentation to the user.
To avoid needing to change the interface of every function that might
generate error diagnostics, the Diagnostics type can be "smuggled" via
an error value through other APIs and then unwrapped at the other end,
though it will lose any naked warnings (without at least one error) along
the way, and so codepaths that are expected to generate warnings
(validation, primarily) should use the concrete Diagnostics type
throughout the call chain.
Martin Atkins