Catch and display error about the --all flag.

Author: ehuss

src/bin/cargo/commands/tree.rs

@@ -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))?;