When we originally stubbed ApplyMoves we didn't know yet how exactly we'd
be using the result, so we made it a double-indexed map allowing looking
up moves in both directions.
However, in practice we only actually need to look up old addresses by new
addresses, and so this commit first removes the double indexing so that
each move is only represented by one element in the map.
We also need to describe situations where a move was blocked, because in
a future commit we'll generate some warnings in those cases. Therefore
ApplyMoves now returns a MoveResults object which contains both a map of
changes and a map of blocks. The map of blocks isn't used yet as of this
commit, but we'll use it in a later commit to produce warnings within
the "terraform" package.
Per our rule that the content of the state can never make a move statement
invalid, our behavior for two objects trying to occupy the same address
will be to just ignore that and let the object already at the address
take priority.
For the moment this is silent from an end-user perspective and appears
only in our internal logs. However, I'm hoping that our future planned
adjustment to the interface of this function will include some way to
allow reporting these collisions in some end-user-visible way, either as
a separate warning per collision or as a single warning that collects
together all of the collisions into a single message somehow.
This situation can arise both because the previous run state already
contained an object at the target address of a move and because more than
one move ends up trying to target the same location. In the latter case,
which one "wins" is decided by our depth-first traversal order, which is
in turn derived from our chaining and nesting rules and is therefore
arbitrary but deterministic.
This new function complements the existing function FindMoveStatements
by potentially generating additional "implied" move statements that aren't
written explicit in the configuration but that we'll infer by comparing
the configuration and te previous run state.
The goal here is to infer only enough to replicate the effect of the
"count boundary fixup" graph node (terraform.NodeCountBoundary) that we
currently use to deal with this concern of preserving the zero-instance
when switching between "count" and not "count".
This is just dead code for now. A subsequent commit will introduce this
into the "terraform" package while also removing
terraform.NodeCountBoundary, thus achieving the same effect as before but
in a way that'll get reported in the UI as a move, using the same language
that we'd use for an explicit move statement.
When originally filling out these test cases we didn't yet have the logic
in place to detect chained moves and so this test couldn't succeed in
spite of being correct.
We now have chain-detection implemented and so consequently we can also
detect cyclic chains. This commit largely just enables the original test
unchanged, although it does include the text of the final error message
for reporting cyclic move chains which wasn't yet finalized when we were
stubbing out this test case originally.
Here we wire through the "move results" into the graph walk data
structures so that all of the the nodes which produce
plans.ResourceInstanceChange values can capture the "PrevRunAddr" for
each resource instance.
This doesn't actually quite work yet, because the logic in Context.Plan
isn't actually correct and so the updated state from
refactoring.ApplyMoves isn't actually visible as the "previous run state".
For that reason, the context test in this commit is currently skipped,
with the intent of re-enabling it once the updated state is properly
propagating into the plan graph walk and thus we can actually react to
the result of the move while choosing actions for those addresses.
This is a first pass at implementing refactoring.ValidateMoves, covering
the main validation rules.
This is not yet complete. A couple situations not yet covered are
represented by commented test cases in TestValidateMoves, although that
isn't necessarily comprehensive. We'll do a further pass of filling this
out with any other subtleties before we ship this feature.
As of this commit, refactoring.ValidateMoves doesn't actually do anything
yet (always returns nil) but the goal here is to wire in the set of all
declared instances so that refactoring.ValidateMoves will then have all
of the information it needs to encapsulate our validation rules.
The actual implementation of refactoring.ValidateMoves will follow in
subsequent commits.
This is a whole lot of nothing right now, just stubbing out some control
flow that ultimately just leads to TODOs that cause it to do nothing at
all.
My intent here is to get this cross-cutting skeleton in place and thus
make it easier for us to collaborate on adding the meat to it, so that
it's more likely we can work on different parts separately and still get
a result that tessellates.
We previously built out addrs.UnifyMoveEndpoints with a different
implementation strategy in mind, but that design turns out to not be
viable because it forces us to move to AbsMoveable addresses too soon,
before we've done the analysis required to identify chained and nested
moves.
Instead, UnifyMoveEndpoints will return a new type MoveEndpointInModule
which conceptually represents a matching pattern which either matches or
doesn't match a particular AbsMoveable. It does this by just binding the
unified relative address from the MoveEndpoint to the module where it
was declared, and thus allows us to distinguish between the part of the
module path which applies to any instances of the given modules vs. the
user-specified part which must identify particular module instances.
Martin Atkins