cli/command: PromptUserForCredentials: print error on terminal restore fail

If restoring the terminal state fails, "echo" no longer works, which means
that anything the user types is no longer shown. The login itself may already
have succeeded, so we should not fail the command, but it's good to inform
the user that this happened, which may give them a clue why things no longer
work as they expect them to work.

With this patch:

    docker login -u yourname
    Password:
    Error: failed to restore terminal state to echo input: something bad happened

    Login Succeeded

We should consider printing instructions how  to restore this manually (other
than restarting the shell). e.g., 'run stty echo' when in a Linux or macOS shell,
but PowerShell and CMD.exe may need different instructions.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

cli/command/registry.go

@@ -161,7 +161,15 @@ func PromptUserForCredentials(ctx context.Context, cli Cli, argUser, argPassword
 		if err != nil {
 			return registrytypes.AuthConfig{}, err
 		}
-		defer restoreInput()
+		defer func() {
+			if err := restoreInput(); err != nil {
+				// TODO(thaJeztah): we should consider printing instructions how
+				//  to restore this manually (other than restarting the shell).
+				//  e.g., 'run stty echo' when in a Linux or macOS shell, but
+				//  PowerShell and CMD.exe may need different instructions.
+				_, _ = fmt.Fprintln(cli.Err(), "Error: failed to restore terminal state to echo input:", err)
+			}
+		}()
 
 		argPassword, err = PromptForInput(ctx, cli.In(), cli.Out(), "Password: ")
 		if err != nil {