feat: Show user defined help flags in hints

This allows display of user-defined help flags during "try 'help'" style
messages

clap_builder/src/error/format.rs

@@ -3,6 +3,8 @@
 #![cfg_attr(not(feature = "error-context"), allow(dead_code))]
 #![cfg_attr(not(feature = "error-context"), allow(unused_imports))]
 
+use std::borrow::Cow;
+
 use crate::builder::Command;
 use crate::builder::StyledStr;
 use crate::builder::Styles;
@@ -12,6 +14,7 @@ use crate::error::ContextKind;
 use crate::error::ContextValue;
 use crate::error::ErrorKind;
 use crate::output::TAB;
+use crate::ArgAction;
 
 /// Defines how to format an error for displaying to the user
 pub trait ErrorFormatter: Sized {
@@ -120,7 +123,7 @@ impl ErrorFormatter for RichFormatter {
             put_usage(&mut styled, usage);
         }
 
-        try_help(&mut styled, styles, error.inner.help_flag);
+        try_help(&mut styled, styles, error.inner.help_flag.as_deref());
 
         styled
     }
@@ -461,7 +464,7 @@ pub(crate) fn format_error_message(
         put_usage(&mut styled, usage);
     }
     if let Some(cmd) = cmd {
-        try_help(&mut styled, styles, get_help_flag(cmd));
+        try_help(&mut styled, styles, get_help_flag(cmd).as_deref());
     }
     styled
 }
@@ -480,16 +483,34 @@ fn put_usage(styled: &mut StyledStr, usage: &StyledStr) {
     styled.push_styled(usage);
 }
 
-pub(crate) fn get_help_flag(cmd: &Command) -> Option<&'static str> {
+pub(crate) fn get_help_flag(cmd: &Command) -> Option<Cow<'static, str>> {
     if !cmd.is_disable_help_flag_set() {
-        Some("--help")
+        Some(Cow::Borrowed("--help"))
+    } else if let Some(flag) = get_user_help_flag(cmd) {
+        Some(Cow::Owned(flag))
     } else if cmd.has_subcommands() && !cmd.is_disable_help_subcommand_set() {
-        Some("help")
+        Some(Cow::Borrowed("help"))
     } else {
         None
     }
 }
 
+fn get_user_help_flag(cmd: &Command) -> Option<String> {
+    let arg = cmd.get_arguments().find(|arg| match arg.get_action() {
+        ArgAction::Help | ArgAction::HelpShort | ArgAction::HelpLong => true,
+        ArgAction::Append
+        | ArgAction::Count
+        | ArgAction::SetTrue
+        | ArgAction::SetFalse
+        | ArgAction::Set
+        | ArgAction::Version => false,
+    })?;
+
+    arg.get_long()
+        .map(|long| format!("--{long}"))
+        .or_else(|| arg.get_short().map(|short| format!("-{short}")))
+}
+
 fn try_help(styled: &mut StyledStr, styles: &Styles, help: Option<&str>) {
     if let Some(help) = help {
         use std::fmt::Write as _;

clap_builder/src/error/mod.rs

@@ -69,7 +69,7 @@ struct ErrorInner {
     context: FlatMap<ContextKind, ContextValue>,
     message: Option<Message>,
     source: Option<Box<dyn error::Error + Send + Sync>>,
-    help_flag: Option<&'static str>,
+    help_flag: Option<Cow<'static, str>>,
     styles: Styles,
     color_when: ColorChoice,
     color_help_when: ColorChoice,
@@ -319,7 +319,7 @@ impl<F: ErrorFormatter> Error<F> {
         self
     }
 
-    pub(crate) fn set_help_flag(mut self, help_flag: Option<&'static str>) -> Self {
+    pub(crate) fn set_help_flag(mut self, help_flag: Option<Cow<'static, str>>) -> Self {
         self.inner.help_flag = help_flag;
         self
     }

tests/builder/help.rs

@@ -373,6 +373,8 @@ fn try_help_custom_flag() {
 error: unexpected argument 'bar' found
 
 Usage: ctest
+
+For more information, try '--help'.
 ";
 
     let cmd = Command::new("ctest")
@@ -394,6 +396,8 @@ fn try_help_custom_flag_short() {
 error: unexpected argument 'bar' found
 
 Usage: ctest
+
+For more information, try '-h'.
 ";
 
     let cmd = Command::new("ctest")
@@ -410,6 +414,8 @@ fn try_help_custom_flag_long() {
 error: unexpected argument 'bar' found
 
 Usage: ctest
+
+For more information, try '--help'.
 ";
 
     let cmd = Command::new("ctest")
@@ -461,7 +467,7 @@ error: unrecognized subcommand 'bar'
 
 Usage: ctest [COMMAND]
 
-For more information, try 'help'.
+For more information, try '--help'.
 ";
 
     let cmd = Command::new("ctest")