imp: adds '[SUBCOMMAND]' to usage strings with only AppSettings::Allo…

…wExternalSubcommands is used with no other subcommands

Closes #1093

src/app/usage.rs

@@ -96,7 +96,7 @@ pub fn create_help_usage(p: &Parser, incl_reqs: bool) -> String {
     // supporting multiple values
     if p.opts.iter().any(|o| o.is_set(ArgSettings::Multiple)) &&
        p.positionals.values().any(|p| !p.is_set(ArgSettings::Required)) &&
-       !p.has_visible_subcommands() && !has_last {
+       !(p.has_visible_subcommands() || p.is_set(AS::AllowExternalSubcommands)) && !has_last {
         usage.push_str(" [--]");
     }
     let not_req_or_hidden =
@@ -131,7 +131,7 @@ pub fn create_help_usage(p: &Parser, incl_reqs: bool) -> String {
     }
 
     // incl_reqs is only false when this function is called recursively
-    if p.has_visible_subcommands() && incl_reqs {
+    if p.has_visible_subcommands() && incl_reqs || p.is_set(AS::AllowExternalSubcommands) {
         if p.is_set(AS::SubcommandsNegateReqs) || p.is_set(AS::ArgsNegateSubcommands) {
             if !p.is_set(AS::ArgsNegateSubcommands) {
                 usage.push_str("\n    ");

tests/app_settings.rs

@@ -5,6 +5,15 @@ use clap::{App, Arg, SubCommand, AppSettings, ErrorKind};
 
 include!("../clap-test.rs");
 
+static ALLOW_EXT_SC: &'static str = "clap-test v1.4.8
+
+USAGE:
+    clap-test [SUBCOMMAND]
+
+FLAGS:
+    -h, --help       Prints help information
+    -V, --version    Prints version information";
+
 static DONT_COLLAPSE_ARGS: &'static str = "clap-test v1.4.8
 
 USAGE:
@@ -651,4 +660,12 @@ fn issue_1066_allow_leading_hyphen_and_unknown_args_option() {
 
     assert!(res.is_err());
     assert_eq!(res.unwrap_err().kind, ErrorKind::UnknownArgument);
+}
+
+#[test]
+fn issue_1093_allow_ext_sc() {
+    let app = App::new("clap-test")
+        .version("v1.4.8")
+        .setting(AppSettings::AllowExternalSubcommands);
+    assert!(test::compare_output(app, "clap-test --help", ALLOW_EXT_SC, false));
 }