pulumi new: Ensure the stack is selected (#2683)

Ensure the stack is selected when using `pulumi new` with an existing
stack (e.g. a stack created on app.pulumi.com).

CHANGELOG.md

@@ -8,6 +8,8 @@
   environment, or your `.aws/credentials` file, etc.
 - The pulumi version update check can be skipped by setting the environment variable
   `PULUMI_SKIP_UPDATE_CHECK` to `1` or `true`.
+- Fix an issue where the stack would not be selected when an existing stack is specified when running
+  `pulumi new <template> -s <existing-stack>`.
 
 ### Improvements
 

cmd/new.go

@@ -25,6 +25,8 @@ import (
 	"strings"
 	"unicode"
 
+	"github.com/pulumi/pulumi/pkg/backend/state"
+
 	"github.com/pulumi/pulumi/pkg/apitype"
 	"github.com/pulumi/pulumi/pkg/backend"
 	"github.com/pulumi/pulumi/pkg/backend/display"
@@ -252,6 +254,11 @@ func newNewCmd() *cobra.Command {
 				}
 			}
 
+			// Ensure the stack is selected.
+			if !generateOnly && s != nil {
+				state.SetCurrentStack(s.Ref().String())
+			}
+
 			// Install dependencies.
 			if !generateOnly {
 				if err := installDependencies(); err != nil {