The `substr` function allows the `length` parameter to be longer than the remaining characters in the input after the offset. This is useful for when you want to truncate a string to a maximum number of characters. However, the documentation isn't clear on this so I had to do a test deployment to confirm the behaviour after finding the behaviour in an old issue https://github.com/hashicorp/terraform/issues/15751
Preconditions and postconditions for resources and data sources may not
refer to the address of the containing resource or data source. This
commit adds a parse-time validation for this rule.
This is not currently gated by the experiment only because it is awkward
to do so in the context of evaluationStateData, which doesn't have any
concept of experiments at the moment.
If the configuration contains preconditions and/or postconditions for any
objects, we'll check them during evaluation of those objects and generate
errors if any do not pass.
The handling of post-conditions is particularly interesting here because
we intentionally evaluate them _after_ we've committed our record of the
resulting side-effects to the state/plan, with the intent that future
plans against the same object will keep failing until the problem is
addressed either by changing the object so it would pass the precondition
or changing the precondition to accept the current object. That then
avoids the need for us to proactively taint managed resources whose
postconditions fail, as we would for provisioner failures: instead, we can
leave the resolution approach up to the user to decide.
Co-authored-by: Alisdair McDiarmid <alisdair@users.noreply.github.com>
If a resource or output value has a precondition or postcondition rule
then anything the condition depends on is a dependency of the object,
because the condition rules will be evaluated as part of visiting the
relevant graph node.
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 construct of a block containing a condition and an error message will
be useful for other sorts of blocks defining expectations or contracts, so
we'll give it a more generic name in anticipation of it being used in
other situations.
