fix: assure submodules are skipped everywhere

gix/src/object/tree/editor.rs

@@ -263,7 +263,7 @@ fn write_cursor<'repo>(cursor: &mut Cursor<'_, 'repo>) -> Result<Id<'repo>, writ
                     id: entry.oid,
                     source: err,
                 })?;
-                if !cursor.repo.has_object(entry.oid) {
+                if !entry.mode.is_commit() && !cursor.repo.has_object(entry.oid) {
                     return Err(write::Error::MissingObject {
                         filename: entry.filename.clone(),
                         kind: entry.mode.into(),

gix/src/reference/errors.rs

@@ -106,6 +106,19 @@ pub mod head_tree_id {
     }
 }
 
+///
+pub mod head_tree {
+    /// The error returned by [`Repository::head_tree`(…)](crate::Repository::head_tree()).
+    #[derive(Debug, thiserror::Error)]
+    #[allow(missing_docs)]
+    pub enum Error {
+        #[error(transparent)]
+        HeadCommit(#[from] crate::reference::head_commit::Error),
+        #[error(transparent)]
+        CommitTree(#[from] crate::object::commit::Error),
+    }
+}
+
 ///
 pub mod find {
     ///

gix/src/reference/mod.rs

@@ -10,7 +10,7 @@ pub mod iter;
 pub mod remote;
 
 mod errors;
-pub use errors::{edit, find, follow, head_commit, head_id, head_tree_id, peel};
+pub use errors::{edit, find, follow, head_commit, head_id, head_tree, head_tree_id, peel};
 
 use crate::ext::ObjectIdExt;
 

gix/src/repository/reference.rs

@@ -215,6 +215,16 @@ impl crate::Repository {
         Ok(self.head_commit()?.tree_id()?)
     }
 
+    /// Return the tree object the `HEAD^{tree}` reference currently points to after peeling it fully,
+    /// following symbolic references and tags until a tree is found.
+    ///
+    /// Note that this may fail for various reasons, most notably because the repository
+    /// is freshly initialized and doesn't have any commits yet. It could also fail if the
+    /// head does not point to a tree, unlikely but possible.
+    pub fn head_tree(&self) -> Result<crate::Tree<'_>, reference::head_tree::Error> {
+        Ok(self.head_commit()?.tree()?)
+    }
+
     /// Find the reference with the given partial or full `name`, like `main`, `HEAD`, `heads/branch` or `origin/other`,
     /// or return an error if it wasn't found.
     ///

gix/tests/gix/repository/object.rs

@@ -118,6 +118,20 @@ mod edit_tree {
         Ok(())
     }
 
+    #[test]
+    fn submodules_are_not_checked_for_existence() -> crate::Result {
+        let repo = crate::named_subrepo_opts("make_submodules.sh", "with-submodules", gix::open::Options::isolated())?
+            .with_object_memory();
+        let mut editor = repo.head_tree()?.edit()?;
+        let actual = editor.write()?;
+        assert_eq!(
+            actual,
+            repo.head_tree_id()?,
+            "Nothing changed, but it did validate the root tree that it would want to write"
+        );
+        Ok(())
+    }
+
     #[test]
     fn missing_objects_and_illformed_path_components_trigger_error() -> crate::Result {
         let (repo, _tmp) = crate::repo_rw("make_packed_and_loose.sh")?;