Merge #11353

11353: Add experimental use plan option to up r=justinvp a=Frassle

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# Description

<!--- Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. -->
Adds an option to use plans in the update prompt:
```
Do you want to perform this update?  [Use arrows to move, type to filter]
> [experimental] yes, using Update Plans (https://pulumi.com/updateplans)
  yes
  no
  details
```

Needs at least pulumi/pulumi-hugo#2230 merged and published first.

Fixes #9687

## Checklist

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- [ ] I have added tests that prove my fix is effective or that my feature works
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User-facing changes require a CHANGELOG entry.
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- [x] I have run `make changelog` and committed the `changelog/pending/<file>` documenting my change
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then the service should honor older versions of the CLI where this change would not exist.
You must then bump the API version in /pkg/backend/httpstate/client/api.go, as well as add
it to the service.
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- [ ] Yes, there are changes in this PR that warrants bumping the Pulumi Service API version
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Co-authored-by: Fraser Waters <fraser@pulumi.com>

changelog/pending/20221115--cli--add-prompt-to-up-to-use-experimental-update-plans.yaml

@@ -0,0 +1,4 @@
+changes:
+- type: feat
+  scope: cli
+  description: Add prompt to `up` to use experimental update plans.

pkg/backend/apply.go

@@ -75,6 +75,7 @@ type response string
 
 const (
 	yes     response = "yes"
+	yesPlan response = "[experimental] yes, using Update Plans (https://pulumi.com/updateplans)"
 	no      response = "no"
 	details response = "details"
 )
@@ -133,14 +134,14 @@ func PreviewThenPrompt(ctx context.Context, kind apitype.UpdateKind, stack Stack
 	}
 
 	// Otherwise, ensure the user wants to proceed.
-	res = confirmBeforeUpdating(kind, stack, events, op.Opts)
+	res, plan = confirmBeforeUpdating(kind, stack, events, plan, op.Opts)
 	close(eventsChannel)
 	return plan, changes, res
 }
 
 // confirmBeforeUpdating asks the user whether to proceed. A nil error means yes.
 func confirmBeforeUpdating(kind apitype.UpdateKind, stack Stack,
-	events []engine.Event, opts UpdateOptions) result.Result {
+	events []engine.Event, plan *deploy.Plan, opts UpdateOptions) (result.Result, *deploy.Plan) {
 	for {
 		var response string
 
@@ -152,6 +153,12 @@ func confirmBeforeUpdating(kind apitype.UpdateKind, stack Stack,
 
 		choices := []string{string(yes), string(no)}
 
+		// If we have a new plan but didn't start with a plan we can prompt to use the new plan.
+		// If we're in experimental mode we don't add this because "yes" will also use the plan
+		if plan != nil && opts.Engine.Plan == nil && !opts.Engine.Experimental {
+			choices = append([]string{string(yesPlan)}, choices...)
+		}
+
 		// For non-previews, we can also offer a detailed summary.
 		if !opts.SkipPreview {
 			choices = append(choices, string(details))
@@ -179,16 +186,23 @@ func confirmBeforeUpdating(kind apitype.UpdateKind, stack Stack,
 			Options: choices,
 			Default: string(no),
 		}, &response, surveyIcons); err != nil {
-			return result.FromError(fmt.Errorf("confirmation cancelled, not proceeding with the %s: %w", kind, err))
+			return result.FromError(fmt.Errorf("confirmation cancelled, not proceeding with the %s: %w", kind, err)), nil
 		}
 
 		if response == string(no) {
 			fmt.Printf("confirmation declined, not proceeding with the %s\n", kind)
-			return result.Bail()
+			return result.Bail(), nil
 		}
 
 		if response == string(yes) {
-			return nil
+			// If we're in experimental mode always use the plan
+			if opts.Engine.Experimental {
+				return nil, plan
+			}
+			return nil, nil
+		}
+		if response == string(yesPlan) {
+			return nil, plan
 		}
 
 		if response == string(details) {
@@ -219,11 +233,11 @@ func PreviewThenPromptThenExecute(ctx context.Context, kind apitype.UpdateKind,
 			return changes, res
 		}
 
-		// If we had an original plan use it, else if experimental use the newly generated plan (might be nil if we've turned
-		// plan generation off)
+		// If we had an original plan use it, else if prompt said to use the plan from Preview then use the
+		// newly generated plan
 		if originalPlan != nil {
 			op.Opts.Engine.Plan = originalPlan
-		} else if op.Opts.Engine.Experimental {
+		} else if plan != nil {
 			op.Opts.Engine.Plan = plan
 		} else {
 			op.Opts.Engine.Plan = nil

pkg/backend/httpstate/backend.go

@@ -1166,7 +1166,7 @@ func (b *cloudBackend) runEngineAction(
 	case apitype.PreviewUpdate:
 		plan, changes, res = engine.Update(u, engineCtx, op.Opts.Engine, true)
 	case apitype.UpdateUpdate:
-		_, changes, res = engine.Update(u, engineCtx, op.Opts.Engine, dryRun)
+		plan, changes, res = engine.Update(u, engineCtx, op.Opts.Engine, dryRun)
 	case apitype.ResourceImportUpdate:
 		_, changes, res = engine.Import(u, engineCtx, op.Opts.Engine, op.Imports, dryRun)
 	case apitype.RefreshUpdate: