* lang: stabilise ephemeral values experiment
Stabilise the ephemeral values experiment and ephemeralasnull
experimental function.
* simplify handling of apply time input vars
As the final step in stabilising the ephemeral values experiment, we can
remove the separate code path for handling input variables supplied via
-var and -var-file during apply.
The intent here is conveyed in the tests: when applying a saved plan,
all ephemeral variables set in the plan (the "apply-time
variables"), must be set, and no others.
As per the TODO copied from the prototype, there is some more work to be
done here in making the handling of undeclared variables during apply as
sophisticated as that during plan, emitting helpful warnings (for
example) when input variables are supplied unnecessarily via environment
variables.
* experiments: officially conclude EV experiment
---------
Co-authored-by: Radek Simko <radek.simko@gmail.com>
When the ephemeral_values experiment is active, a module author can
designate individual input variables and output values as being
"ephemeral", which doesn't currently do anything but in future commits
will represent that the values can be used only in locations that don't
require Terraform to persist the value as part of state snapshots or
saved plan files.
The optional modifier previously accepted a single argument: the
attribute type. This commit adds an optional second argument, which
specifies a default value for the attribute.
To record the default values for a variable's type, we use a separate
parallel structure of `typeexpr.Defaults`, rather than extending
`cty.Type` to include a `cty.Value` of defaults (which may in turn
include a `cty.Type` with defaults, and so on, and so forth).
The new `typeexpr.TypeConstraintWithDefaults` returns a type constraint
and defaults value. Defaults will be `nil` unless there are default
values specified somewhere in the variable's type.
This allows precondition and postcondition checks to be declared for
resources and output values as long as the preconditions_postconditions
experiment is enabled.
Terraform Core doesn't currently know anything about these features, so
as of this commit declaring them does nothing at all.
This is part of a general effort to move all of Terraform's non-library
package surface under internal in order to reinforce that these are for
internal use within Terraform only.
If you were previously importing packages under this prefix into an
external codebase, you could pin to an earlier release tag as an interim
solution until you've make a plan to achieve the same functionality some
other way.
