feat(error): Add a 'render' method

CHANGELOG.md

@@ -272,6 +272,7 @@ Behavior Changes
 - Can now pass runtime generated data to `Command`, `Arg`, `ArgGroup`, `PossibleValue`, etc without managing lifetimes with the `string` feature flag (#2150, #4223)
 - New default `error-context`, `help` and `usage` feature flags that can be turned off for smaller binaries (#4236)
 - *(error)* `Error::apply` for changing the formatter for dropping binary size (#4111)
+- *(error)* `Command::render`
 - *(help)* Show `PossibleValue::help` in long help (`--help`) (#3312)
 - *(help)* New `{tab}` variable for `Command::help_template` (#4161)
 - *(help)* `Command::render_help` and `Command::render_long_help`

src/error/mod.rs

@@ -195,6 +195,27 @@ impl<F: ErrorFormatter> Error<F> {
         c.print()
     }
 
+    /// Render the error message to a [`StyledStr`].
+    ///
+    /// # Example
+    /// ```no_run
+    /// use clap::Command;
+    ///
+    /// match Command::new("Command").try_get_matches() {
+    ///     Ok(matches) => {
+    ///         // do_something
+    ///     },
+    ///     Err(err) => {
+    ///         let err = err.render();
+    ///         println!("{}", err);
+    ///         // do_something
+    ///     },
+    /// };
+    /// ```
+    pub fn render(&self) -> StyledStr {
+        self.formatted().into_owned()
+    }
+
     fn new(kind: ErrorKind) -> Self {
         Self {
             inner: Box::new(ErrorInner {