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.
Init should only _add_ values, not remove them.
During graph execution, there are steps that expect that a state isn't
being actively pruned out from under it. Namely: writing deposed states.
Writing deposed states has no way to handle if a state changes
underneath it because the only way to uniquely identify a deposed state
is its index in the deposed array. When destroying deposed resources, we
set the value to `<nil>`. If the array is pruned before the next deposed
destroy, then the indexes have changed, and this can cause a crash.
This PR does the following (with more details below):
* `init()` no longer prunes.
* `ReadState()` always prunes before returning. I can't think of a
scenario where this is unsafe since generally we can always START
from a pruned state, its just causing problems to prune
mid-execution.
* Exported State APIs updated to be robust against nil ModuleStates.
Instead, I think we should adopt the following semantics for init/prune
in our structures that support it (Diff, for example). By having
consistent semantics around these functions, we can avoid this in the
future and have set expectations working with them.
* `init()` (in anything) will only ever be additive, and won't change
ordering or existing values. It won't remove values.
* `prune()` is destructive, expectedly.
* Functions on a structure must not assume a pruned structure 100% of
the time. They must be robust to handle nils. This is especially
important because in many cases values such as `Modules` in state
are exported so end users can simply modify them outside of the
exported APIs.
This PR may expose us to unknown crashes but I've tried to cover our
cases in exposed APIs by checking for nil.
