plans: indicate when resource deleted due to move (#31695)

Add a new ChangeReason, ReasonDeleteBecauseNoMoveTarget, to provide better
information in cases where a planned deletion is due to moving a resource to
a target not in configuration.

Consider a case in which a resource instance exists in state at address A, and
the user adds a moved block to move A to address B. Whether by the user's
intention or not, address B does not exist in configuration.
Terraform combines the move from A to B, and the lack of configuration for B,
into a single delete action for the (previously nonexistent) entity B.
Prior to this commit, the Terraform plan will report that resource B will be
destroyed because it does not exist in configuration, without explicitly
connecting this to the move.

This commit provides the user an additional clue as to what has happened, in a
case in which Terraform has elided a user's action and inaction into one
potentially destructive change.

internal/command/format/diff.go

@@ -115,6 +115,8 @@ func ResourceChange(
 		switch change.ActionReason {
 		case plans.ResourceInstanceDeleteBecauseNoResourceConfig:
 			buf.WriteString(fmt.Sprintf("\n  # (because %s is not in configuration)", addr.Resource.Resource))
+		case plans.ResourceInstanceDeleteBecauseNoMoveTarget:
+			buf.WriteString(fmt.Sprintf("\n  # (because %s was moved to %s, which is not in configuration)", change.PrevRunAddr, addr.Resource.Resource))
 		case plans.ResourceInstanceDeleteBecauseNoModule:
 			// FIXME: Ideally we'd truncate addr.Module to reflect the earliest
 			// step that doesn't exist, so it's clearer which call this refers

internal/command/jsonplan/plan.go

@@ -413,6 +413,8 @@ func (p *plan) marshalResourceChanges(resources []*plans.ResourceInstanceChangeS
 			r.ActionReason = "delete_because_each_key"
 		case plans.ResourceInstanceDeleteBecauseNoModule:
 			r.ActionReason = "delete_because_no_module"
+		case plans.ResourceInstanceDeleteBecauseNoMoveTarget:
+			r.ActionReason = "delete_because_no_move_target"
 		case plans.ResourceInstanceReadBecauseConfigUnknown:
 			r.ActionReason = "read_because_config_unknown"
 		case plans.ResourceInstanceReadBecauseDependencyPending:

internal/command/views/json/change.go

@@ -80,6 +80,7 @@ const (
 	ReasonDeleteBecauseCountIndex       ChangeReason = "delete_because_count_index"
 	ReasonDeleteBecauseEachKey          ChangeReason = "delete_because_each_key"
 	ReasonDeleteBecauseNoModule         ChangeReason = "delete_because_no_module"
+	ReasonDeleteBecauseNoMoveTarget     ChangeReason = "delete_because_no_move_target"
 	ReasonReadBecauseConfigUnknown      ChangeReason = "read_because_config_unknown"
 	ReasonReadBecauseDependencyPending  ChangeReason = "read_because_dependency_pending"
 )
@@ -108,6 +109,8 @@ func changeReason(reason plans.ResourceInstanceChangeActionReason) ChangeReason
 		return ReasonDeleteBecauseNoModule
 	case plans.ResourceInstanceReadBecauseConfigUnknown:
 		return ReasonReadBecauseConfigUnknown
+	case plans.ResourceInstanceDeleteBecauseNoMoveTarget:
+		return ReasonDeleteBecauseNoMoveTarget
 	case plans.ResourceInstanceReadBecauseDependencyPending:
 		return ReasonReadBecauseDependencyPending
 	default:

internal/plans/changes.go

@@ -427,6 +427,12 @@ const (
 	// specific reasons for a particular instance to no longer be declared.
 	ResourceInstanceDeleteBecauseNoModule ResourceInstanceChangeActionReason = 'M'
 
+	// ResourceInstanceDeleteBecauseNoMoveTarget indicates that the resource
+	// address appears as the target ("to") in a moved block, but no
+	// configuration exists for that resource. According to our move rules,
+	// this combination evaluates to a deletion of the "new" resource.
+	ResourceInstanceDeleteBecauseNoMoveTarget ResourceInstanceChangeActionReason = 'A'
+
 	// ResourceInstanceReadBecauseConfigUnknown indicates that the resource
 	// must be read during apply (rather than during planning) because its
 	// configuration contains unknown values. This reason applies only to

internal/plans/internal/planproto/planfile.proto

@@ -151,6 +151,7 @@ enum ResourceInstanceActionReason {
     REPLACE_BY_TRIGGERS = 9;
     READ_BECAUSE_CONFIG_UNKNOWN = 10;
     READ_BECAUSE_DEPENDENCY_PENDING = 11;
+    DELETE_BECAUSE_NO_MOVE_TARGET = 12;
 }
 
 message ResourceInstanceChange {

internal/plans/planfile/tfplan.go

@@ -331,6 +331,8 @@ func resourceChangeFromTfplan(rawChange *planproto.ResourceInstanceChange) (*pla
 		ret.ActionReason = plans.ResourceInstanceReadBecauseConfigUnknown
 	case planproto.ResourceInstanceActionReason_READ_BECAUSE_DEPENDENCY_PENDING:
 		ret.ActionReason = plans.ResourceInstanceReadBecauseDependencyPending
+	case planproto.ResourceInstanceActionReason_DELETE_BECAUSE_NO_MOVE_TARGET:
+		ret.ActionReason = plans.ResourceInstanceDeleteBecauseNoMoveTarget
 	default:
 		return nil, fmt.Errorf("resource has invalid action reason %s", rawChange.ActionReason)
 	}
@@ -705,6 +707,8 @@ func resourceChangeToTfplan(change *plans.ResourceInstanceChangeSrc) (*planproto
 		ret.ActionReason = planproto.ResourceInstanceActionReason_READ_BECAUSE_CONFIG_UNKNOWN
 	case plans.ResourceInstanceReadBecauseDependencyPending:
 		ret.ActionReason = planproto.ResourceInstanceActionReason_READ_BECAUSE_DEPENDENCY_PENDING
+	case plans.ResourceInstanceDeleteBecauseNoMoveTarget:
+		ret.ActionReason = planproto.ResourceInstanceActionReason_DELETE_BECAUSE_NO_MOVE_TARGET
 	default:
 		return nil, fmt.Errorf("resource %s has unsupported action reason %s", change.Addr, change.ActionReason)
 	}

internal/terraform/node_resource_plan_orphan.go

@@ -157,6 +157,13 @@ func (n *NodePlannableResourceInstanceOrphan) managedResourceExecute(ctx EvalCon
 func (n *NodePlannableResourceInstanceOrphan) deleteActionReason(ctx EvalContext) plans.ResourceInstanceChangeActionReason {
 	cfg := n.Config
 	if cfg == nil {
+		if !n.Addr.Equal(n.prevRunAddr(ctx)) {
+			// This means the resource was moved - see also
+			// ResourceInstanceChange.Moved() which calculates
+			// this the same way.
+			return plans.ResourceInstanceDeleteBecauseNoMoveTarget
+		}
+
 		return plans.ResourceInstanceDeleteBecauseNoResourceConfig
 	}