json-output: Add output changes to plan logs

Extend the outputs JSON log message to support an `action` field (and
make the `type` and `value` fields optional). This allows us to emit a
useful output change summary as part of the plan, bringing the JSON log
output into parity with the text output.

While we do have access to the before/after values in the output
changes, attempting to wedge those into a structured log message is not
appropriate. That level of detail can be extracted from the JSON plan
output from `terraform show -json`.

internal/command/views/json/output.go

@@ -6,14 +6,16 @@ import (
 
 	ctyjson "github.com/zclconf/go-cty/cty/json"
 
+	"github.com/hashicorp/terraform/internal/plans"
 	"github.com/hashicorp/terraform/internal/states"
 	"github.com/hashicorp/terraform/internal/tfdiags"
 )
 
 type Output struct {
 	Sensitive bool            `json:"sensitive"`
-	Type      json.RawMessage `json:"type"`
-	Value     json.RawMessage `json:"value"`
+	Type      json.RawMessage `json:"type,omitempty"`
+	Value     json.RawMessage `json:"value,omitempty"`
+	Action    ChangeAction    `json:"action,omitempty"`
 }
 
 type Outputs map[string]Output
@@ -50,6 +52,19 @@ func OutputsFromMap(outputValues map[string]*states.OutputValue) (Outputs, tfdia
 	return outputs, nil
 }
 
+func OutputsFromChanges(changes []*plans.OutputChangeSrc) Outputs {
+	outputs := make(map[string]Output, len(changes))
+
+	for _, change := range changes {
+		outputs[change.Addr.OutputValue.Name] = Output{
+			Sensitive: change.Sensitive,
+			Action:    changeAction(change.Action),
+		}
+	}
+
+	return outputs
+}
+
 func (o Outputs) String() string {
 	return fmt.Sprintf("Outputs: %d", len(o))
 }

internal/command/views/json/output_test.go

@@ -5,7 +5,9 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/hashicorp/terraform/internal/addrs"
 	"github.com/hashicorp/terraform/internal/lang/marks"
+	"github.com/hashicorp/terraform/internal/plans"
 	"github.com/hashicorp/terraform/internal/states"
 	"github.com/zclconf/go-cty/cty"
 )
@@ -69,6 +71,95 @@ func TestOutputsFromMap(t *testing.T) {
 	}
 }
 
+func TestOutputsFromChanges(t *testing.T) {
+	root := addrs.RootModuleInstance
+	num, err := plans.NewDynamicValue(cty.NumberIntVal(1234), cty.Number)
+	str, err := plans.NewDynamicValue(cty.StringVal("1234"), cty.String)
+	if err != nil {
+		t.Fatalf("unexpected error creating dynamic value: %v", err)
+	}
+
+	got := OutputsFromChanges([]*plans.OutputChangeSrc{
+		// Unchanged output "boop", value 1234
+		{
+			Addr: root.OutputValue("boop"),
+			ChangeSrc: plans.ChangeSrc{
+				Action: plans.NoOp,
+				Before: num,
+				After:  num,
+			},
+			Sensitive: false,
+		},
+		// New output "beep", value 1234
+		{
+			Addr: root.OutputValue("beep"),
+			ChangeSrc: plans.ChangeSrc{
+				Action: plans.Create,
+				Before: nil,
+				After:  num,
+			},
+			Sensitive: false,
+		},
+		// Deleted output "blorp", prior value 1234
+		{
+			Addr: root.OutputValue("blorp"),
+			ChangeSrc: plans.ChangeSrc{
+				Action: plans.Delete,
+				Before: num,
+				After:  nil,
+			},
+			Sensitive: false,
+		},
+		// Updated output "honk", prior value 1234, new value "1234"
+		{
+			Addr: root.OutputValue("honk"),
+			ChangeSrc: plans.ChangeSrc{
+				Action: plans.Update,
+				Before: num,
+				After:  str,
+			},
+			Sensitive: false,
+		},
+		// New sensitive output "secret", value "1234"
+		{
+			Addr: root.OutputValue("secret"),
+			ChangeSrc: plans.ChangeSrc{
+				Action: plans.Create,
+				Before: nil,
+				After:  str,
+			},
+			Sensitive: true,
+		},
+	})
+
+	want := Outputs{
+		"boop": {
+			Action:    "noop",
+			Sensitive: false,
+		},
+		"beep": {
+			Action:    "create",
+			Sensitive: false,
+		},
+		"blorp": {
+			Action:    "delete",
+			Sensitive: false,
+		},
+		"honk": {
+			Action:    "update",
+			Sensitive: false,
+		},
+		"secret": {
+			Action:    "create",
+			Sensitive: true,
+		},
+	}
+
+	if !cmp.Equal(want, got) {
+		t.Fatalf("unexpected result\n%s", cmp.Diff(want, got))
+	}
+}
+
 func TestOutputs_String(t *testing.T) {
 	outputs := Outputs{
 		"boop": {

internal/command/views/operation.go

@@ -195,6 +195,17 @@ func (v *OperationJSON) Plan(plan *plans.Plan, schemas *terraform.Schemas) {
 	}
 
 	v.view.ChangeSummary(cs)
+
+	var rootModuleOutputs []*plans.OutputChangeSrc
+	for _, output := range plan.Changes.Outputs {
+		if !output.Addr.Module.IsRoot() {
+			continue
+		}
+		rootModuleOutputs = append(rootModuleOutputs, output)
+	}
+	if len(rootModuleOutputs) > 0 {
+		v.view.Outputs(json.OutputsFromChanges(rootModuleOutputs))
+	}
 }
 
 func (v *OperationJSON) resourceDrift(oldState, newState *states.State, schemas *terraform.Schemas) error {

internal/command/views/operation_test.go

@@ -763,6 +763,90 @@ func TestOperationJSON_planDrift(t *testing.T) {
 	testJSONViewOutputEquals(t, done(t).Stdout(), want)
 }
 
+func TestOperationJSON_planOutputChanges(t *testing.T) {
+	streams, done := terminal.StreamsForTesting(t)
+	v := &OperationJSON{view: NewJSONView(NewView(streams))}
+
+	root := addrs.RootModuleInstance
+
+	plan := &plans.Plan{
+		Changes: &plans.Changes{
+			Resources: []*plans.ResourceInstanceChangeSrc{},
+			Outputs: []*plans.OutputChangeSrc{
+				{
+					Addr: root.OutputValue("boop"),
+					ChangeSrc: plans.ChangeSrc{
+						Action: plans.NoOp,
+					},
+				},
+				{
+					Addr: root.OutputValue("beep"),
+					ChangeSrc: plans.ChangeSrc{
+						Action: plans.Create,
+					},
+				},
+				{
+					Addr: root.OutputValue("bonk"),
+					ChangeSrc: plans.ChangeSrc{
+						Action: plans.Delete,
+					},
+				},
+				{
+					Addr: root.OutputValue("honk"),
+					ChangeSrc: plans.ChangeSrc{
+						Action: plans.Update,
+					},
+					Sensitive: true,
+				},
+			},
+		},
+	}
+	v.Plan(plan, testSchemas())
+
+	want := []map[string]interface{}{
+		// No resource changes
+		{
+			"@level":   "info",
+			"@message": "Plan: 0 to add, 0 to change, 0 to destroy.",
+			"@module":  "terraform.ui",
+			"type":     "change_summary",
+			"changes": map[string]interface{}{
+				"operation": "plan",
+				"add":       float64(0),
+				"change":    float64(0),
+				"remove":    float64(0),
+			},
+		},
+		// Output changes
+		{
+			"@level":   "info",
+			"@message": "Outputs: 4",
+			"@module":  "terraform.ui",
+			"type":     "outputs",
+			"outputs": map[string]interface{}{
+				"boop": map[string]interface{}{
+					"action":    "noop",
+					"sensitive": false,
+				},
+				"beep": map[string]interface{}{
+					"action":    "create",
+					"sensitive": false,
+				},
+				"bonk": map[string]interface{}{
+					"action":    "delete",
+					"sensitive": false,
+				},
+				"honk": map[string]interface{}{
+					"action":    "update",
+					"sensitive": true,
+				},
+			},
+		},
+	}
+
+	testJSONViewOutputEquals(t, done(t).Stdout(), want)
+}
+
 func TestOperationJSON_plannedChange(t *testing.T) {
 	streams, done := terminal.StreamsForTesting(t)
 	v := &OperationJSON{view: NewJSONView(NewView(streams))}

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

@@ -185,10 +185,11 @@ Terraform outputs a change summary when a plan or apply operation completes. Bot
 
 ## Outputs
 
-After a successful apply, a message with type `outputs` contains the values of all root module output values. This message contains an `outputs` object, the keys of which are the output names. The outputs values are objects with the following keys:
+After a successful plan or apply, a message with type `outputs` contains the values of all root module output values. This message contains an `outputs` object, the keys of which are the output names. The outputs values are objects with the following keys:
 
-- `value:` the value of the output, encoded in JSON
-- `type`: the detected HCL type of the output value
+- `action`: for planned outputs, the action which will be taken for the output. Values: `noop`, `create`, `update`, `delete`
+- `value`: for applied outputs, the value of the output, encoded in JSON
+- `type`: for applied outputs, the detected HCL type of the output value
 - `sensitive`: boolean value, `true` if the output is sensitive and should be hidden from UI by default
 
 Note that `sensitive` outputs still include the `value` field, and integrating software should respect the sensitivity value as appropriate for the given use case.