feat: add Repository::checkout_options().

It's a low-level set of options to drive (quite unsafe) checkouts.
They are unsafe as they may be configured to overwrite, and are in no
way similar to `git checkout`.

Author: Byron

gix/src/clone/checkout.rs

@@ -118,9 +118,7 @@ pub mod main_worktree {
                 })?;
             let mut index = gix_index::File::from_state(index, repo.index_path());
 
-            let mut opts = repo
-                .config
-                .checkout_options(repo, gix_worktree::stack::state::attributes::Source::IdMapping)?;
+            let mut opts = repo.checkout_options(gix_worktree::stack::state::attributes::Source::IdMapping)?;
             opts.destination_is_initially_empty = true;
 
             let mut files = progress.add_child_with_id("checkout".to_string(), ProgressId::CheckoutFiles.into());

gix/src/repository/checkout.rs

@@ -0,0 +1,14 @@
+use crate::{config, Repository};
+
+impl Repository {
+    /// Return options that can be used to drive a low-level checkout operation.
+    /// Use `attributes_source` to determine where `.gitattributes` files should be read from, which depends on
+    /// the presence of a worktree to begin with.
+    /// Here, typically this value would be [`gix_worktree::stack::state::attributes::Source::IdMapping`]
+    pub fn checkout_options(
+        &self,
+        attributes_source: gix_worktree::stack::state::attributes::Source,
+    ) -> Result<gix_worktree_state::checkout::Options, config::checkout_options::Error> {
+        self.config.checkout_options(self, attributes_source)
+    }
+}

gix/src/repository/mod.rs

@@ -20,7 +20,10 @@ pub enum Kind {
 #[cfg(any(feature = "attributes", feature = "excludes"))]
 pub mod attributes;
 mod cache;
+#[cfg(feature = "worktree-mutation")]
+mod checkout;
 mod config;
+
 ///
 #[cfg(feature = "blob-diff")]
 mod diff;