feat: Add Command::mut_subcommands

clap_builder/src/builder/command.rs

@@ -386,6 +386,51 @@ impl Command {
         self
     }
 
+    /// Allows one to mutate all [`Command`]s after they've been added as subcommands.
+    ///
+    /// This does not affect the built-in `--help` or `--version` arguments.
+    ///
+    /// # Examples
+    ///
+    #[cfg_attr(feature = "string", doc = "```")]
+    #[cfg_attr(not(feature = "string"), doc = "```ignore")]
+    /// # use clap_builder as clap;
+    /// # use clap::{Command, Arg, ArgAction};
+    ///
+    /// let mut cmd = Command::new("foo")
+    ///     .subcommands([
+    ///         Command::new("fetch"),
+    ///         Command::new("push"),
+    ///     ])
+    ///     // Allow title-case subcommands
+    ///     .mut_subcommands(|sub| {
+    ///         let name = sub.get_name();
+    ///         let alias = name.chars().enumerate().map(|(i, c)| {
+    ///             if i == 0 {
+    ///                 c.to_ascii_uppercase()
+    ///             } else {
+    ///                 c
+    ///             }
+    ///         }).collect::<String>();
+    ///         sub.alias(alias)
+    ///     });
+    ///
+    /// let res = cmd.try_get_matches_from_mut(vec!["foo", "fetch"]);
+    /// assert!(res.is_ok());
+    ///
+    /// let res = cmd.try_get_matches_from_mut(vec!["foo", "Fetch"]);
+    /// assert!(res.is_ok());
+    /// ```
+    #[must_use]
+    #[cfg_attr(debug_assertions, track_caller)]
+    pub fn mut_subcommands<F>(mut self, f: F) -> Self
+    where
+        F: FnMut(Command) -> Command,
+    {
+        self.subcommands = self.subcommands.into_iter().map(f).collect();
+        self
+    }
+
     /// Adds an [`ArgGroup`] to the application.
     ///
     /// [`ArgGroup`]s are a family of related arguments.