Our state models cannot store unknown values (since state only deals with
knowns) and so following the lead of recent similar changes for resource
instances we'll treat the planned changeset as a sort of overlay on the
state, preferring values stored there if present, and then write in basic
planned output changes to the plan when we evaluate them.
We're abusing the plan model a little here: its current design is intended
to lay the groundwork for a future release where output values have a
full lifecycle similar to resource instances where we can properly track
changes during the plan phase, but the rest of Terraform isn't yet ready
for that and so we'll just retain an approximation of the planned action
by only using Create and Destroy actions.
A future release should change this so that output changes can be tracked
accurately using an approach similar to that of resource instances.
During the plan operation we need to retain _somewhere_ the planned
changes for all outputs so we can refer to them during expression
evaluation. For consistency with how we handle resource instance changes,
we'll keep them in the plan so we can properly retain unknown values,
which cannot be written to state.
As with output values in the state, only root output plans are retained
in a round-trip through the on-disk plan file format, but that's okay
because we can trivially re-calculate all of these during apply. We
include the _root_ outputs in the plan file only because they are
externally-visible side effects that ought to be included in any rendering
of the plan made from the plan file for user inspection.
We've intentionally changed the behavior for "count = 1" so that it'll
assign an index to the created instance even though there's only one. The
un-indexed behavior now applies only if count isn't set _at all_, thus
avoiding weird behavior if a count is _dynamically_ set to 1 via an
expression but is assumed to be a list elsewhere in configuration.
We previously tried to take a shortcut for an empty diff, just returning
the given value directly. This is incorrect in the weird case where we're
creating a new instance but it has no attributes (and thus an empty diff)
because in that case we'd return the given null value, turning the result
into a no-op or destroy change.
To fix this, we just always do the work to construct a new value, even
if we might end up doing all this just to reconstruct the same value we
started with in some cases.
This allows the provider to distinguish whether a particular value is set
in configuration or whether it's coming from prior state. It has no
particular purpose other than that.
We often want to bail out of a test if diagnostics are present, and it's
easiest to debug that when the diagnostics are printed in a compact but
complete manner that is non-trivial to produce.
Rather than duplicating that diagnostic formatting in every test, these
helpers allow us to succinctly print diagnostics and bail out when they
are present.
This is a pretty basic attempt to turn a pair of values into an old-school
diff. It probably won't work correctly for all tests, but hopefully works
well enough that we can just update the remaining tests in-place to use
the new API directly.
We now handle impure functions by having them return an unknown value
during plan, since we can't predict what the value will be during apply.
This test was assuming the old behavior.
The provider is allowed to return a partial result if it also includes
error diagnostics. Real providers still return at least a null value in
that case due to the RPC format, but test mocks are often more sloppy.
Since the refresh walk creates a partial plan to account for objects that
are yet to be created, we need to provide at least a basic mock of the
PlanProviderChange provider method.
For now we're using the old-style "DiffFn" shim interface since that's
already available for use in other tests.
It's not possible for a normal RPC-based provider to get into this
situation because a nil value can't go over the wire, but it's easy to
cause this by not correctly configuring a provider mock during tests.
By panicking early here we produce a more helpful error message and stack
trace than we'd otherwise produce if we let this nil value escape out
into the rest of Terraform.
Significant changes to the provider interface left a lot of the
tests in a non-buildable state. This set of changes gets the
tests building again but does not attempt to make them run to
completion or pass.
After this commit, it is possible to build a test program for
the ./terraform package but it will panic during its run. That
will be addressed in subsequent commits.
Since we do our deletes using a separate graph node from all of the other
actions, and a "Replace" change implies both a delete _and_ a create, we
need to pretend at apply time that a single replace change was actually
two separate changes.
This will also early-exit eval if a destroy node finds a non-Delete change
or if an apply node finds a Delete change. These should not happen in
practice because we leave these nodes out of the graph when they are not
needed for the given action, but we do this here for robustness so as not
to have an invisible dependency between the graph builder and the eval
phase.
When we're working on a create or destroy change it's expected for one of
the values to be null. Here we mimick the pre-0.12 behavior of producing
just an empty map in that case, which the helper/schema code (now the only
caller of this shim) then ignores completely.
For PreApply hook purposes we only actually use the Delete, Create, and
Update actions, because other actions are handled in different ways than
a direct call to ApplyResourceChange.
However, if there's a bug in core that causes it to pass a different
action, it's better for us to mark it as being explicitly unknown in the
UI rather than simply defaulting to "Modifying...", which can thus obscure
the problem and make for a confusing result.
The "id" field is assumed to always exist, and must have a valid value.
Set "id" to unknown when planning new resource changes to indicate that
it will be computed.
Prior to our refactoring here, we were relying on a lucky coincidence for
correct behavior of the plan walk following a refresh in the same run:
- The refresh phase created placeholder objects in the state to represent
any resource instance pending creation, to allow the interpolator to
read attributes from them when evaluating "provider" and "data" blocks.
In effect, the refresh walk is creating a partial plan that only covers
creation actions, but was immediately discarding the actual diff entries
and storing only the planned new state.
- It happened that objects pending creation showed up in state with an
empty ID value, since that only gets assigned by the provider during
apply.
- The Refresh function concluded by calling terraform.State.Prune, which
deletes from the state any objects that have an empty ID value, which
therefore prevented these temporary objects from surviving into the
plan phase.
After refactoring, we no longer have this special ID field on instance
object state, and we instead rely on the Status field for tracking such
things. We also no longer have an explicit "prune" step on state, since
the state mutation methods themselves keep the structure pruned.
To address this, here we introduce a new instance object status "planned",
which is equivalent to having an empty ID value in the old world. We also
introduce a new method on states.SyncState that deletes from the state
any planned objects, which therefore replaces that portion of the old
State.prune operation just for this refresh use-case.
Finally, we are now expecting the expression evaluator to pull pending
objects from the planned changeset rather than from the state directly,
and so for correct results these placeholder resource creation changes
must also be reported in a throwaway changeset during the refresh walk.
The addition of states.ObjectPlanned also permits a previously-missing
safety check in the expression evaluator to prevent us from relying on the
incomplete value stored in state for a pending object, in the event that
some bug prevents the real pending object from being written into the
planned changeset.
We no longer use strings to represent addresses, so this method was a
leftover outlier from previous refactoring efforts.
At this time the result is not actually being used due to the state type
refactoring, which is a bug we'll address in a subsequent commit.
We'll now show an "update" symbol prior to the argument to this synthetic
jsonencode(...) call, for consistency with how we show nested values in
other cases and to attach a verb to any "# forces replacement".
We'll also show a special form in the case where the value seems to differ
only in whitespace, so users can understand what's going on in that
hopefully-rare situation, particularly if those whitespace-only changes
end up forcing us to replace a remote object.
Martin Atkins