assure submodule status doesn't operate if there is no worktree checkout

gix/src/submodule/mod.rs

@@ -382,6 +382,9 @@ pub mod status {
                 return Ok(status);
             }
 
+            if !state.worktree_checkout {
+                return Ok(status);
+            }
             let statusses = adjust_options(sm_repo.status(gix_features::progress::Discard)?)
                 .index_worktree_options_mut(|opts| {
                     if ignore == config::Ignore::Untracked {
@@ -408,7 +411,7 @@ pub mod status {
         /// Return `None` if the repository clone or the worktree are missing entirely, which would leave
         /// it to the caller to determine if that's considered dirty or not.
         pub fn is_dirty(&self) -> Option<bool> {
-            if !self.state.worktree_checkout && !self.state.repository_exists {
+            if !self.state.worktree_checkout || !self.state.repository_exists {
                 return None;
             }
             let is_dirty =

gix/tests/fixtures/make_submodules.sh

@@ -21,6 +21,15 @@ git init submodule-head-changed
   cd m1 && git checkout @~1
 )
 
+git init submodule-head-changed-no-worktree
+(cd submodule-head-changed-no-worktree
+  git submodule add ../module1 m1
+  git commit -m "add submodule"
+
+  (cd m1 && git checkout @~1)
+  rm -Rf m1 && mkdir m1
+)
+
 git init modified-and-untracked
 (cd modified-and-untracked
   git submodule add ../module1 m1

gix/tests/submodule/mod.rs

@@ -63,7 +63,7 @@ mod open {
                         worktree_checkout: false,
                         superproject_configuration: true,
                     },
-                    Some(true),
+                    None,
                 )],
             ),
         ] {
@@ -241,6 +241,39 @@ mod open {
             Ok(())
         }
 
+        #[test]
+        fn changed_head_empty_worktree() -> crate::Result {
+            let repo = repo("submodule-head-changed-no-worktree")?;
+            let sm = repo.submodules()?.into_iter().flatten().next().expect("one submodule");
+
+            let status = sm.status(gix::submodule::config::Ignore::None, false)?;
+            assert_eq!(
+                status.state,
+                gix::submodule::State {
+                    repository_exists: true,
+                    is_old_form: false,
+                    worktree_checkout: false,
+                    superproject_configuration: true,
+                }
+            );
+            assert_eq!(
+                status.is_dirty(),
+                None,
+                "a missing worktree counts as no-dirty, even though the checked out HEAD changed. \
+                 Git does the same, even though as we express it as 'not determined'"
+            );
+            assert_ne!(
+                status.index_id, status.checked_out_head_id,
+                "not considered dirty despite head mismatch"
+            );
+            assert!(
+                status.changes.is_none(),
+                "Detailed changes are never done if there is no worktree"
+            );
+
+            Ok(())
+        }
+
         #[test]
         fn is_dirty_skips_expensive_checks() -> crate::Result {
             let repo = repo("submodule-head-changed-and-modified")?;