feat: show banner when workspace is outdated (#4926)

* feat: show banner when workspace is outdated

* Address PR comments

* Fix: writer

cli/ssh.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"net/url"
 	"os"
 	"path/filepath"
 	"strings"
@@ -72,6 +73,11 @@ func ssh() *cobra.Command {
 				return err
 			}
 
+			updateWorkspaceBanner, outdated := verifyWorkspaceOutdated(client, workspace)
+			if outdated && isTTYErr(cmd) {
+				_, _ = fmt.Fprintln(cmd.ErrOrStderr(), updateWorkspaceBanner)
+			}
+
 			// OpenSSH passes stderr directly to the calling TTY.
 			// This is required in "stdio" mode so a connecting indicator can be displayed.
 			err = cliui.Agent(ctx, cmd.ErrOrStderr(), cliui.AgentOptions{
@@ -343,3 +349,18 @@ func notifyCondition(ctx context.Context, client *codersdk.Client, workspaceID u
 		return deadline.Truncate(time.Minute), callback
 	}
 }
+
+// Verify if the user workspace is outdated and prepare an actionable message for user.
+func verifyWorkspaceOutdated(client *codersdk.Client, workspace codersdk.Workspace) (string, bool) {
+	if !workspace.Outdated {
+		return "", false // workspace is up-to-date
+	}
+
+	workspaceLink := buildWorkspaceLink(client.URL, workspace)
+	return fmt.Sprintf("👋 Your workspace is outdated! Update it here: %s\n", workspaceLink), true
+}
+
+// Build the user workspace link which navigates to the Coder web UI.
+func buildWorkspaceLink(serverURL *url.URL, workspace codersdk.Workspace) *url.URL {
+	return serverURL.ResolveReference(&url.URL{Path: fmt.Sprintf("@%s/%s", workspace.OwnerName, workspace.Name)})
+}