fix(help): Subcommand help looks like --help

Like was said in clap-rs#2435, this is what people would expect.

While we should note this in a compatibility section in the changelog, I
do not consider this a breaking change since we should be free to adjust
the help output as needed.  We are cautious when people might build up
their own content around it (like clap-rs#3312) but apps should already handle
this with `--help` so this shouldn't be a major change.

We aren't offering a way for people to disable this, assuming people
won't need to.  Longer term, we are looking at support "Actions" (clap-rs#3405)
and expect those to help customize the flags.  We'll need something
similar for the `help` subcommand.

Fixes clap-rs#3440

examples/tutorial_builder/03_04_subcommands.rs

@@ -3,7 +3,6 @@ use clap::{app_from_crate, arg, App, AppSettings};
 fn main() {
     let matches = app_from_crate!()
         .propagate_version(true)
-        .global_setting(AppSettings::UseLongFormatForHelpSubcommand)
         .setting(AppSettings::SubcommandRequiredElseHelp)
         .subcommand(
             App::new("add")

examples/tutorial_derive/03_04_subcommands.rs

@@ -1,9 +1,8 @@
-use clap::{AppSettings, Parser, Subcommand};
+use clap::{Parser, Subcommand};
 
 #[derive(Parser)]
 #[clap(author, version, about, long_about = None)]
 #[clap(propagate_version = true)]
-#[clap(global_setting(AppSettings::UseLongFormatForHelpSubcommand))]
 struct Cli {
     #[clap(subcommand)]
     command: Commands,

src/build/app_settings.rs

@@ -176,26 +176,8 @@ pub enum AppSettings {
     )]
     AllowInvalidUtf8ForExternalSubcommands,
 
-    /// Specifies that the help subcommand should print the long help message (`--help`).
-    ///
-    /// **NOTE:** This setting is useless if [`AppSettings::DisableHelpSubcommand`] or [`AppSettings::NoAutoHelp`] is set,
-    /// or if the app contains no subcommands at all.
-    ///
-    /// # Examples
-    ///
-    /// ```rust
-    /// # use clap::{App, Arg, AppSettings};
-    /// App::new("myprog")
-    ///     .global_setting(AppSettings::UseLongFormatForHelpSubcommand)
-    ///     .subcommand(App::new("test")
-    ///         .arg(Arg::new("foo")
-    ///             .help("short form about message")
-    ///             .long_help("long form about message")
-    ///         )
-    ///     )
-    ///     .get_matches();
-    /// ```
-    /// [long format]: crate::App::long_about
+    /// Deprecated, this is now the default
+    #[deprecated(since = "3.1.0", note = "This is now the default")]
     UseLongFormatForHelpSubcommand,
 
     /// Deprecated, replaced with [`App::subcommand_negates_reqs`] and

src/parse/parser.rs

@@ -661,7 +661,7 @@ impl<'help, 'app> Parser<'help, 'app> {
 
         let parser = Parser::new(&mut sc);
 
-        Err(parser.help_err(self.app.is_set(AS::UseLongFormatForHelpSubcommand)))
+        Err(parser.help_err(true))
     }
 
     fn is_new_arg(&self, next: &RawOsStr, current_positional: &Arg) -> bool {

tests/builder/app_settings.rs

@@ -79,54 +79,6 @@ SUBCOMMANDS:
     info    
 ";
 
-static LONG_FORMAT_FOR_HELP_SUBCOMMAND: &str = "myprog-test 
-
-USAGE:
-    myprog test [foo]
-
-ARGS:
-    <foo>
-            long form help message
-
-OPTIONS:
-    -h, --help
-            Print help information
-";
-
-static LONG_FORMAT_FOR_NESTED_HELP_SUBCOMMAND: &str = "myprog-test-nested 
-long form about message
-
-USAGE:
-    myprog test nested
-
-OPTIONS:
-    -h, --help
-            Print help information
-";
-
-static LONG_FORMAT_SINGLE_ARG_HELP_SUBCOMMAND: &str = "myprog 1.0
-
-USAGE:
-    myprog [foo] [SUBCOMMAND]
-
-ARGS:
-    <foo>
-            long form help message
-
-OPTIONS:
-    -h, --help
-            Print help information
-
-    -V, --version
-            Print version information
-
-SUBCOMMANDS:
-    help
-            Print this message or the help of the given subcommand(s)
-    test
-            
-";
-
 #[test]
 fn setting() {
     #![allow(deprecated)]
@@ -1137,63 +1089,6 @@ fn aaos_option_use_delim_false() {
     );
 }
 
-#[test]
-fn nested_help_subcommand_with_global_setting() {
-    let m = App::new("myprog")
-        .global_setting(AppSettings::UseLongFormatForHelpSubcommand)
-        .subcommand(
-            App::new("test").subcommand(
-                App::new("nested")
-                    .about("short form about message")
-                    .long_about("long form about message"),
-            ),
-        );
-    assert!(utils::compare_output(
-        m,
-        "myprog test help nested",
-        LONG_FORMAT_FOR_NESTED_HELP_SUBCOMMAND,
-        false
-    ));
-}
-
-#[test]
-fn single_arg_help_with_long_format_setting() {
-    let m = App::new("myprog")
-        .version("1.0")
-        .setting(AppSettings::UseLongFormatForHelpSubcommand)
-        .subcommand(App::new("test"))
-        .arg(
-            Arg::new("foo")
-                .help("short form help message")
-                .long_help("long form help message"),
-        );
-    assert!(utils::compare_output(
-        m,
-        "myprog help",
-        LONG_FORMAT_SINGLE_ARG_HELP_SUBCOMMAND,
-        false
-    ));
-}
-
-#[test]
-fn use_long_format_for_help_subcommand_with_setting() {
-    let m = App::new("myprog")
-        .setting(AppSettings::UseLongFormatForHelpSubcommand)
-        .subcommand(
-            App::new("test").arg(
-                Arg::new("foo")
-                    .help("short form help message")
-                    .long_help("long form help message"),
-            ),
-        );
-    assert!(utils::compare_output(
-        m,
-        "myprog help test",
-        LONG_FORMAT_FOR_HELP_SUBCOMMAND,
-        false
-    ));
-}
-
 #[test]
 fn no_auto_help() {
     let app = App::new("myprog")

tests/derive/structopt.rs

@@ -7,7 +7,6 @@ fn compatible() {
     #[derive(StructOpt)]
     #[structopt(author, version, about)]
     #[structopt(global_setting(AppSettings::PropagateVersion))]
-    #[structopt(global_setting(AppSettings::UseLongFormatForHelpSubcommand))]
     struct Cli {
         #[structopt(subcommand)]
         command: Commands,