added "en" command

Fixes #1655

src/cli/en.rs

@@ -0,0 +1,58 @@
+use std::path::PathBuf;
+use crate::cli::exec::Exec;
+
+use crate::env;
+
+/// starts a new shell with the mise environment built from the current configuration
+///
+/// This is an alternative to `mise activate` that allows you to explicitly start a mise session.
+/// It will have the tools and environment variables in the configs loaded.
+/// Note that changing directories will not update the mise environment.
+#[derive(Debug, clap::Args)]
+#[clap(verbatim_doc_comment, after_long_help = AFTER_LONG_HELP)]
+pub struct En {
+    /// Directory to start the shell in
+    #[clap(default_value = ".", verbatim_doc_comment)]
+    pub dir: PathBuf,
+
+    /// Shell to start
+    ///
+    /// Defaults to $SHELL
+    #[clap(verbatim_doc_comment, long, short = 's')]
+    pub shell: Option<String>,
+}
+
+impl En {
+    pub fn run(self) -> eyre::Result<()> {
+        let shell = self.shell.or_else(|| {
+            match env::var("SHELL") {
+                Ok(shell) => {
+                    let shell_type = shell.split('/').last().unwrap_or(&shell);
+                    let shell = match shell_type {
+                        "fish" => format!("{shell} -N"),
+                        _ => shell,
+                    };
+                    Some(shell)
+                }
+                Err(_) => None,
+            }
+        }).unwrap_or("sh".into());
+        env::set_current_dir(&self.dir)?;
+        Exec {
+            tool: vec![],
+            raw: false,
+            jobs: None,
+            c: Some(shell.into()),
+            command: None,
+        }.run()
+    }
+}
+
+static AFTER_LONG_HELP: &str = color_print::cstr!(
+    r#"<bold><underline>Examples:</underline></bold>
+
+    $ <bold>mise en .</bold>
+    $ <bold>node -v</bold>
+    v20.0.0
+"#
+);

src/cli/mod.rs

@@ -16,6 +16,7 @@ mod current;
 mod deactivate;
 mod direnv;
 mod doctor;
+mod en;
 mod env;
 pub mod exec;
 mod external;
@@ -70,6 +71,7 @@ pub enum Commands {
     Deactivate(deactivate::Deactivate),
     Direnv(direnv::Direnv),
     Doctor(doctor::Doctor),
+    En(en::En),
     Env(env::Env),
     Exec(exec::Exec),
     Global(global::Global),
@@ -125,6 +127,7 @@ impl Commands {
             Self::Deactivate(cmd) => cmd.run(),
             Self::Direnv(cmd) => cmd.run(),
             Self::Doctor(cmd) => cmd.run(),
+            Self::En(cmd) => cmd.run(),
             Self::Env(cmd) => cmd.run(),
             Self::Exec(cmd) => cmd.run(),
             Self::Global(cmd) => cmd.run(),