json-output: Add change reasons to explain deletes

The extra feedback information for why resource instance deletion is
planned is now included in the streaming JSON UI output.

We also add an explicit case for no-op actions to switch statements in
this package to ensure exhaustiveness, for future linting.

internal/command/views/json/change.go

@@ -73,6 +73,12 @@ const (
 	ReasonRequested    ChangeReason = "requested"
 	ReasonCannotUpdate ChangeReason = "cannot_update"
 	ReasonUnknown      ChangeReason = "unknown"
+
+	ReasonDeleteBecauseNoResourceConfig ChangeReason = "delete_because_no_resource_config"
+	ReasonDeleteBecauseWrongRepetition  ChangeReason = "delete_because_wrong_repetition"
+	ReasonDeleteBecauseCountIndex       ChangeReason = "delete_because_count_index"
+	ReasonDeleteBecauseEachKey          ChangeReason = "delete_because_each_key"
+	ReasonDeleteBecauseNoModule         ChangeReason = "delete_because_no_module"
 )
 
 func changeReason(reason plans.ResourceInstanceChangeActionReason) ChangeReason {
@@ -85,6 +91,16 @@ func changeReason(reason plans.ResourceInstanceChangeActionReason) ChangeReason
 		return ReasonRequested
 	case plans.ResourceInstanceReplaceBecauseCannotUpdate:
 		return ReasonCannotUpdate
+	case plans.ResourceInstanceDeleteBecauseNoResourceConfig:
+		return ReasonDeleteBecauseNoResourceConfig
+	case plans.ResourceInstanceDeleteBecauseWrongRepetition:
+		return ReasonDeleteBecauseWrongRepetition
+	case plans.ResourceInstanceDeleteBecauseCountIndex:
+		return ReasonDeleteBecauseCountIndex
+	case plans.ResourceInstanceDeleteBecauseEachKey:
+		return ReasonDeleteBecauseEachKey
+	case plans.ResourceInstanceDeleteBecauseNoModule:
+		return ReasonDeleteBecauseNoModule
 	default:
 		// This should never happen, but there's no good way to guarantee
 		// exhaustive handling of the enum, so a generic fall back is better

internal/command/views/json/hook.go

@@ -314,6 +314,10 @@ func startActionVerb(action plans.Action) string {
 		// This is not currently possible to reach, as we receive separate
 		// passes for create and delete
 		return "Replacing"
+	case plans.NoOp:
+		// This should never be possible: a no-op planned change should not
+		// be applied. We'll fall back to "Applying".
+		fallthrough
 	default:
 		return "Applying"
 	}
@@ -336,6 +340,10 @@ func progressActionVerb(action plans.Action) string {
 		// This is not currently possible to reach, as we receive separate
 		// passes for create and delete
 		return "replacing"
+	case plans.NoOp:
+		// This should never be possible: a no-op planned change should not
+		// be applied. We'll fall back to "applying".
+		fallthrough
 	default:
 		return "applying"
 	}
@@ -358,6 +366,10 @@ func actionNoun(action plans.Action) string {
 		// This is not currently possible to reach, as we receive separate
 		// passes for create and delete
 		return "Replacement"
+	case plans.NoOp:
+		// This should never be possible: a no-op planned change should not
+		// be applied. We'll fall back to "Apply".
+		fallthrough
 	default:
 		return "Apply"
 	}

website/docs/internals/machine-readable-ui.html.md

@@ -126,10 +126,15 @@ At the end of a plan or before an apply, Terraform will emit a `planned_change`
 - `resource`: object describing the address of the resource to be changed; see [resource object](#resource-object) below for details
 - `previous_resource`: object describing the previous address of the resource, if this change includes a configuration-driven move
 - `action`: the action planned to be taken for the resource. Values: `noop`, `create`, `read`, `update`, `replace`, `delete`, `move`.
-- `reason`: an optional reason for the change, currently only used when the action is `replace`. Values:
+- `reason`: an optional reason for the change, currently only used when the action is `replace` or `delete`. Values:
     - `tainted`: resource was marked as tainted
     - `requested`: user requested that the resource be replaced, for example via the `-replace` plan flag
     - `cannot_update`: changes to configuration force the resource to be deleted and created rather than updated
+    - `delete_because_no_resource_config`: no matching resource in configuration
+    - `delete_because_wrong_repetition`: resource instance key has no corresponding `count` or `for_each` in configuration
+    - `delete_because_count_index`: resource instance key is outside the range of the `count` argument
+    - `delete_because_each_key`: resource instance key is not included in the `for_each` argument
+    - `delete_because_no_module`: enclosing module instance is not in configuration
 
 This message does not include details about the exact changes which caused the change to be planned. That information is available in [the JSON plan output](./json-format.html).