message: Catch and display error about the --all flag.
diff: @@ -12,6 +12,7 @@ pub fn cli() -> App {
  "Display the tree for all packages in the workspace",
  "Exclude specific workspace members",
  )
  + .arg(Arg::with_name("all").long("all").short("a").hidden(true))
  .arg_features()
  .arg_target_triple(
  "Filter dependencies matching the given target-triple (default host platform)",
  @@ -72,6 +73,13 @@ pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
  )
  .into());
  }
  + if args.is_present("all") {
  + return Err(anyhow::format_err!(
  + "The `cargo tree` --all flag has been changed to --no-dedupe.\n\
  + If you are looking to display all workspace members, use the --workspace flag."
  + )
  + .into());
  + }
  let ws = args.workspace(config)?;
  let charset = tree::Charset::from_str(args.value_of("charset").unwrap())
  .map_err(|e| anyhow::anyhow!("{}", e))?;
  