Ensure you never drop the working commit with --skip-empty

See jj-vcs#2766 for discussions

lib/src/rewrite.rs

@@ -158,7 +158,11 @@ pub fn rebase_commit_with_options(
             }
             EmptyBehaviour::AbandonAllEmpty => *parent.tree_id() == new_tree_id,
         };
-        if should_abandon {
+        // If the user runs `jj checkout foo`, then `jj rebase -s foo -d bar`, and we drop the
+        // checked out empty commit, then the user will unknowingly have done the equivalent of
+        // `jj edit foo` instead of `jj checkout foo`.
+        // Thus, we never allow dropping the working commit. See #2766 and #2760 for discussions.
+        if should_abandon && !mut_repo.view().is_wc_commit_id(&old_commit.id()) {
             // Record old_commit as being succeeded by the parent.
             // This ensures that when we stack commits, the second commit knows to
             // rebase on top of the parent commit, rather than the abandoned commit.

lib/tests/test_rewrite.rs

@@ -1621,7 +1621,9 @@ fn test_rebase_commit_via_rebase_api() {
 
     // Rebase B onto B2
     //
-    // C
+    // D (empty)  E (WC, empty)
+    // |         /
+    // C---------
     // |
     // B B2
     // |/
@@ -1636,12 +1638,26 @@ fn test_rebase_commit_via_rebase_api() {
         .set_parents(vec![commit_b.id().clone()])
         .write()
         .unwrap();
+    let commit_d = create_random_commit(tx.mut_repo(), &settings)
+        .set_parents(vec![commit_c.id().clone()])
+        .set_tree_id(commit_c.tree_id().clone())
+        .write()
+        .unwrap();
+    let commit_e = create_random_commit(tx.mut_repo(), &settings)
+        .set_parents(vec![commit_c.id().clone()])
+        .set_tree_id(commit_c.tree_id().clone())
+        .write()
+        .unwrap();
     let commit_b2 = create_random_commit(tx.mut_repo(), &settings)
         .set_parents(vec![commit_a.id().clone()])
         .set_tree_id(commit_b.tree_id().clone())
         .write()
         .unwrap();
 
+    tx.mut_repo()
+        .set_wc_commit(WorkspaceId::new("ws".to_string()), commit_e.id().clone())
+        .unwrap();
+
     let rebase_options = RebaseOptions {
         empty: EmptyBehaviour::AbandonAllEmpty,
     };
@@ -1657,12 +1673,15 @@ fn test_rebase_commit_via_rebase_api() {
         .mut_repo()
         .rebase_descendants_with_options_return_map(&settings, rebase_options)
         .unwrap();
-    assert_eq!(rebase_map.len(), 1);
+    assert_eq!(rebase_map.len(), 3);
     let new_commit_c =
         assert_rebased_onto(tx.mut_repo(), &rebase_map, &commit_c, &[&commit_b2.id()]);
+    assert_abandoned_with_parent(tx.mut_repo(), &rebase_map, &commit_d, new_commit_c.id());
+    let new_commit_e =
+        assert_rebased_onto(tx.mut_repo(), &rebase_map, &commit_e, &[&new_commit_c.id()]);
 
     assert_eq!(
         *tx.mut_repo().view().heads(),
-        hashset! {new_commit_c.id().clone()}
+        hashset! {new_commit_e.id().clone()}
     );
 }