command: Render "moved" annotations in plan UI

For resources which are planned to move, render the previous run address
as additional information in the plan UI. For the case of a move-only
resource (which otherwise is unchanged), we also render that as a
planned change, but without any corresponding action symbol.

If all changes in the plan are moves without changes, the plan is no
longer considered "empty". In this case, we skip rendering the action
symbols in the UI.

internal/command/format/diff.go

@@ -72,13 +72,27 @@ func ResourceChange(
 			// Some extra context about this unusual situation.
 			buf.WriteString(color.Color("\n  # (left over from a partially-failed replacement of this instance)"))
 		}
+	case plans.NoOp:
+		if change.Moved() {
+			buf.WriteString(color.Color(fmt.Sprintf("[bold]  # %s[reset] has moved to [bold]%s[reset]", change.PrevRunAddr.String(), dispAddr)))
+			break
+		}
+		fallthrough
 	default:
 		// should never happen, since the above is exhaustive
 		buf.WriteString(fmt.Sprintf("%s has an action the plan renderer doesn't support (this is a bug)", dispAddr))
 	}
 	buf.WriteString(color.Color("[reset]\n"))
 
+	if change.Moved() && change.Action != plans.NoOp {
+		buf.WriteString(color.Color(fmt.Sprintf("[bold]  # [reset]([bold]%s[reset] has moved to [bold]%s[reset])\n", change.PrevRunAddr.String(), dispAddr)))
+	}
+
+	if change.Moved() && change.Action == plans.NoOp {
+		buf.WriteString("    ")
+	} else {
 		buf.WriteString(color.Color(DiffActionSymbol(change.Action)) + " ")
+	}
 
 	switch addr.Resource.Resource.Mode {
 	case addrs.ManagedResourceMode:

internal/command/format/diff_test.go

@@ -4448,6 +4448,79 @@ func TestResourceChange_sensitiveVariable(t *testing.T) {
 	runTestCases(t, testCases)
 }
 
+func TestResourceChange_moved(t *testing.T) {
+	prevRunAddr := addrs.Resource{
+		Mode: addrs.ManagedResourceMode,
+		Type: "test_instance",
+		Name: "previous",
+	}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance)
+
+	testCases := map[string]testCase{
+		"moved and updated": {
+			PrevRunAddr: prevRunAddr,
+			Action:      plans.Update,
+			Mode:        addrs.ManagedResourceMode,
+			Before: cty.ObjectVal(map[string]cty.Value{
+				"id":  cty.StringVal("12345"),
+				"foo": cty.StringVal("hello"),
+				"bar": cty.StringVal("baz"),
+			}),
+			After: cty.ObjectVal(map[string]cty.Value{
+				"id":  cty.StringVal("12345"),
+				"foo": cty.StringVal("hello"),
+				"bar": cty.StringVal("boop"),
+			}),
+			Schema: &configschema.Block{
+				Attributes: map[string]*configschema.Attribute{
+					"id":  {Type: cty.String, Computed: true},
+					"foo": {Type: cty.String, Optional: true},
+					"bar": {Type: cty.String, Optional: true},
+				},
+			},
+			RequiredReplace: cty.NewPathSet(),
+			ExpectedOutput: `  # test_instance.example will be updated in-place
+  # (test_instance.previous has moved to test_instance.example)
+  ~ resource "test_instance" "example" {
+      ~ bar = "baz" -> "boop"
+        id  = "12345"
+        # (1 unchanged attribute hidden)
+    }
+`,
+		},
+		"moved without changes": {
+			PrevRunAddr: prevRunAddr,
+			Action:      plans.NoOp,
+			Mode:        addrs.ManagedResourceMode,
+			Before: cty.ObjectVal(map[string]cty.Value{
+				"id":  cty.StringVal("12345"),
+				"foo": cty.StringVal("hello"),
+				"bar": cty.StringVal("baz"),
+			}),
+			After: cty.ObjectVal(map[string]cty.Value{
+				"id":  cty.StringVal("12345"),
+				"foo": cty.StringVal("hello"),
+				"bar": cty.StringVal("baz"),
+			}),
+			Schema: &configschema.Block{
+				Attributes: map[string]*configschema.Attribute{
+					"id":  {Type: cty.String, Computed: true},
+					"foo": {Type: cty.String, Optional: true},
+					"bar": {Type: cty.String, Optional: true},
+				},
+			},
+			RequiredReplace: cty.NewPathSet(),
+			ExpectedOutput: `  # test_instance.previous has moved to test_instance.example
+    resource "test_instance" "example" {
+        id  = "12345"
+        # (2 unchanged attributes hidden)
+    }
+`,
+		},
+	}
+
+	runTestCases(t, testCases)
+}
+
 type testCase struct {
 	Action          plans.Action
 	ActionReason    plans.ResourceInstanceChangeActionReason
@@ -4460,6 +4533,7 @@ type testCase struct {
 	Schema          *configschema.Block
 	RequiredReplace cty.PathSet
 	ExpectedOutput  string
+	PrevRunAddr     addrs.AbsResourceInstance
 }
 
 func runTestCases(t *testing.T, testCases map[string]testCase) {
@@ -4493,12 +4567,22 @@ func runTestCases(t *testing.T, testCases map[string]testCase) {
 				t.Fatal(err)
 			}
 
-			change := &plans.ResourceInstanceChangeSrc{
-				Addr: addrs.Resource{
+			addr := addrs.Resource{
 				Mode: tc.Mode,
 				Type: "test_instance",
 				Name: "example",
-				}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance),
+			}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance)
+
+			prevRunAddr := tc.PrevRunAddr
+			// If no previous run address is given, reuse the current address
+			// to make initialization easier
+			if prevRunAddr.Resource.Resource.Type == "" {
+				prevRunAddr = addr
+			}
+
+			change := &plans.ResourceInstanceChangeSrc{
+				Addr:        addr,
+				PrevRunAddr: prevRunAddr,
 				DeposedKey:  tc.DeposedKey,
 				ProviderAddr: addrs.AbsProviderConfig{
 					Provider: addrs.NewDefaultProvider("test"),

internal/command/views/plan.go

@@ -116,7 +116,7 @@ func renderPlan(plan *plans.Plan, schemas *terraform.Schemas, view *View) {
 	counts := map[plans.Action]int{}
 	var rChanges []*plans.ResourceInstanceChangeSrc
 	for _, change := range plan.Changes.Resources {
-		if change.Action == plans.NoOp {
+		if change.Action == plans.NoOp && !change.Moved() {
 			continue // We don't show anything for no-op changes
 		}
 		if change.Action == plans.Delete && change.Addr.Resource.Resource.Mode == addrs.DataResourceMode {
@@ -125,8 +125,12 @@ func renderPlan(plan *plans.Plan, schemas *terraform.Schemas, view *View) {
 		}
 
 		rChanges = append(rChanges, change)
+
+		// Don't count move-only changes
+		if change.Action != plans.NoOp {
 			counts[change.Action]++
 		}
+	}
 	var changedRootModuleOutputs []*plans.OutputChangeSrc
 	for _, output := range plan.Changes.Outputs {
 		if !output.Addr.Module.IsRoot() {
@@ -138,7 +142,7 @@ func renderPlan(plan *plans.Plan, schemas *terraform.Schemas, view *View) {
 		changedRootModuleOutputs = append(changedRootModuleOutputs, output)
 	}
 
-	if len(counts) == 0 && len(changedRootModuleOutputs) == 0 {
+	if len(rChanges) == 0 && len(changedRootModuleOutputs) == 0 {
 		// If we didn't find any changes to report at all then this is a
 		// "No changes" plan. How we'll present this depends on whether
 		// the plan is "applyable" and, if so, whether it had refresh changes
@@ -225,7 +229,7 @@ func renderPlan(plan *plans.Plan, schemas *terraform.Schemas, view *View) {
 		view.streams.Println("")
 	}
 
-	if len(counts) != 0 {
+	if len(counts) > 0 {
 		headerBuf := &bytes.Buffer{}
 		fmt.Fprintf(headerBuf, "\n%s\n", strings.TrimSpace(format.WordWrap(planHeaderIntro, view.outputColumns())))
 		if counts[plans.Create] > 0 {
@@ -247,9 +251,11 @@ func renderPlan(plan *plans.Plan, schemas *terraform.Schemas, view *View) {
 			fmt.Fprintf(headerBuf, "%s read (data resources)\n", format.DiffActionSymbol(plans.Read))
 		}
 
-		view.streams.Println(view.colorize.Color(headerBuf.String()))
+		view.streams.Print(view.colorize.Color(headerBuf.String()))
+	}
 
-		view.streams.Printf("Terraform will perform the following actions:\n\n")
+	if len(rChanges) > 0 {
+		view.streams.Printf("\nTerraform will perform the following actions:\n\n")
 
 		// Note: we're modifying the backing slice of this plan object in-place
 		// here. The ordering of resource changes in a plan is not significant,
@@ -265,7 +271,7 @@ func renderPlan(plan *plans.Plan, schemas *terraform.Schemas, view *View) {
 		})
 
 		for _, rcs := range rChanges {
-			if rcs.Action == plans.NoOp {
+			if rcs.Action == plans.NoOp && !rcs.Moved() {
 				continue
 			}
 

internal/command/views/plan_test.go

@@ -63,12 +63,15 @@ func testPlan(t *testing.T) *plans.Plan {
 	}
 
 	changes := plans.NewChanges()
-	changes.SyncWrapper().AppendResourceInstanceChange(&plans.ResourceInstanceChangeSrc{
-		Addr: addrs.Resource{
+	addr := addrs.Resource{
 		Mode: addrs.ManagedResourceMode,
 		Type: "test_resource",
 		Name: "foo",
-		}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance),
+	}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance)
+
+	changes.SyncWrapper().AppendResourceInstanceChange(&plans.ResourceInstanceChangeSrc{
+		Addr:        addr,
+		PrevRunAddr: addr,
 		ProviderAddr: addrs.AbsProviderConfig{
 			Provider: addrs.NewDefaultProvider("test"),
 			Module:   addrs.RootModule,

internal/plans/changes.go

@@ -33,7 +33,7 @@ func NewChanges() *Changes {
 
 func (c *Changes) Empty() bool {
 	for _, res := range c.Resources {
-		if res.Action != NoOp {
+		if res.Action != NoOp || res.Moved() {
 			return false
 		}
 	}

internal/plans/changes_src.go

@@ -125,6 +125,10 @@ func (rcs *ResourceInstanceChangeSrc) DeepCopy() *ResourceInstanceChangeSrc {
 	return &ret
 }
 
+func (rcs *ResourceInstanceChangeSrc) Moved() bool {
+	return !rcs.Addr.Equal(rcs.PrevRunAddr)
+}
+
 // OutputChangeSrc describes a change to an output value.
 type OutputChangeSrc struct {
 	// Addr is the absolute address of the output value that the change

internal/plans/changes_test.go

@@ -4,10 +4,127 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/hashicorp/terraform/internal/addrs"
 	"github.com/hashicorp/terraform/internal/lang/marks"
 	"github.com/zclconf/go-cty/cty"
 )
 
+func TestChangesEmpty(t *testing.T) {
+	testCases := map[string]struct {
+		changes *Changes
+		want    bool
+	}{
+		"no changes": {
+			&Changes{},
+			true,
+		},
+		"resource change": {
+			&Changes{
+				Resources: []*ResourceInstanceChangeSrc{
+					{
+						Addr: addrs.Resource{
+							Mode: addrs.ManagedResourceMode,
+							Type: "test_thing",
+							Name: "woot",
+						}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance),
+						PrevRunAddr: addrs.Resource{
+							Mode: addrs.ManagedResourceMode,
+							Type: "test_thing",
+							Name: "woot",
+						}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance),
+						ChangeSrc: ChangeSrc{
+							Action: Update,
+						},
+					},
+				},
+			},
+			false,
+		},
+		"resource change with no-op action": {
+			&Changes{
+				Resources: []*ResourceInstanceChangeSrc{
+					{
+						Addr: addrs.Resource{
+							Mode: addrs.ManagedResourceMode,
+							Type: "test_thing",
+							Name: "woot",
+						}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance),
+						PrevRunAddr: addrs.Resource{
+							Mode: addrs.ManagedResourceMode,
+							Type: "test_thing",
+							Name: "woot",
+						}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance),
+						ChangeSrc: ChangeSrc{
+							Action: NoOp,
+						},
+					},
+				},
+			},
+			true,
+		},
+		"resource moved with no-op change": {
+			&Changes{
+				Resources: []*ResourceInstanceChangeSrc{
+					{
+						Addr: addrs.Resource{
+							Mode: addrs.ManagedResourceMode,
+							Type: "test_thing",
+							Name: "woot",
+						}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance),
+						PrevRunAddr: addrs.Resource{
+							Mode: addrs.ManagedResourceMode,
+							Type: "test_thing",
+							Name: "toot",
+						}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance),
+						ChangeSrc: ChangeSrc{
+							Action: NoOp,
+						},
+					},
+				},
+			},
+			false,
+		},
+		"output change": {
+			&Changes{
+				Outputs: []*OutputChangeSrc{
+					{
+						Addr: addrs.OutputValue{
+							Name: "result",
+						}.Absolute(addrs.RootModuleInstance),
+						ChangeSrc: ChangeSrc{
+							Action: Update,
+						},
+					},
+				},
+			},
+			false,
+		},
+		"output change no-op": {
+			&Changes{
+				Outputs: []*OutputChangeSrc{
+					{
+						Addr: addrs.OutputValue{
+							Name: "result",
+						}.Absolute(addrs.RootModuleInstance),
+						ChangeSrc: ChangeSrc{
+							Action: NoOp,
+						},
+					},
+				},
+			},
+			true,
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			if got, want := tc.changes.Empty(), tc.want; got != want {
+				t.Fatalf("unexpected result: got %v, want %v", got, want)
+			}
+		})
+	}
+}
+
 func TestChangeEncodeSensitive(t *testing.T) {
 	testVals := []cty.Value{
 		cty.ObjectVal(map[string]cty.Value{