feat: Return help message as String for Command

src/builder/command.rs

@@ -708,6 +708,52 @@ impl<'help> App<'help> {
         c.print()
     }
 
+    /// Returns the help message (`-h`).
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use clap::Command;
+    /// let mut cmd = Command::new("myprog");
+    /// let help: String = cmd.render_help();
+    /// print!("{}",help);
+    /// ```
+    pub fn render_help(&mut self) -> String {
+        self._build_self();
+
+        let mut help: String = "".into();
+        let usage = Usage::new(self);
+        match Help::new(HelpWriter::String(&mut help), self, &usage, false).write_help() {
+            Ok(_) => help,
+            Err(e) => {
+                panic!("{}", e.to_string())
+            }
+        }
+    }
+
+    /// Returns the long help message.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use clap::Command;
+    /// let mut cmd = Command::new("myprog");
+    /// let help: String = cmd.render_long_help();
+    /// print!("{}",help);
+    /// ```
+    pub fn render_long_help(&mut self) -> String {
+        self._build_self();
+
+        let mut help: String = "".into();
+        let usage = Usage::new(self);
+        match Help::new(HelpWriter::String(&mut help), self, &usage, true).write_help() {
+            Ok(_) => help,
+            Err(e) => {
+                panic!("{}", e.to_string())
+            }
+        }
+    }
+
     /// Prints the long help message (`--help`) to [`io::stdout()`].
     ///
     /// See also [`Command::print_help`].

src/output/help.rs

@@ -129,6 +129,10 @@ macro_rules! write_method {
                 Ok(())
             }
             HelpWriter::Normal(w) => w.write_all($msg.as_ref()),
+            HelpWriter::String(s) => {
+                s.push_str($msg.into().as_str());
+                Ok(())
+            }
         }
     };
 }
@@ -1117,6 +1121,7 @@ const TAB_WIDTH: usize = 4;
 pub(crate) enum HelpWriter<'writer> {
     Normal(&'writer mut dyn Write),
     Buffer(&'writer mut Colorizer),
+    String(&'writer mut String),
 }
 
 fn should_show_arg(use_long: bool, arg: &Arg) -> bool {

tests/builder/help.rs

@@ -606,6 +606,33 @@ SUBCOMMANDS:
     sub     short about sub
 ";
 
+static SETUP_HELP_MESSAGE: &str = "test 1.3
+Kevin K.
+tests stuff
+
+USAGE:
+    test
+
+OPTIONS:
+    -h, --help       Print help information
+    -V, --version    Print version information
+";
+
+static SETUP_LONG_HELP_MESSAGE: &str = "test 1.3
+Kevin K.
+tests stuff
+
+USAGE:
+    test
+
+OPTIONS:
+    -h, --help
+            Print help information
+
+    -V, --version
+            Print version information
+";
+
 fn setup() -> Command<'static> {
     Command::new("test")
         .author("Kevin K.")
@@ -2896,3 +2923,17 @@ fn display_name_subcommand_explicit() {
         Some("child.display")
     );
 }
+
+#[test]
+fn get_help_as_string() {
+    let cmd = &mut setup();
+    let help = cmd.render_help();
+    assert_eq!(help, SETUP_HELP_MESSAGE);
+}
+
+#[test]
+fn get_long_help_as_string() {
+    let cmd = &mut setup();
+    let help = cmd.render_long_help();
+    assert_eq!(help, SETUP_LONG_HELP_MESSAGE);
+}