repo: abandon working copy only if no other workspaces reference it

Currently, if two workspaces are editing the same discardable commit and
one of them switches to editing a different commit, it is abandoned even
though the other workspace is still editing it. This commit treats
workspaces as referencing their working-copy commits so that they won't
be abandoned.

lib/src/repo.rs

@@ -1325,10 +1325,17 @@ impl MutableRepo {
         &mut self,
         workspace_id: &WorkspaceId,
     ) -> Result<(), EditCommitError> {
-        fn local_branch_target_ids(view: &View) -> impl Iterator<Item = &CommitId> {
-            view.local_branches()
-                .flat_map(|(_, target)| target.added_ids())
-        }
+        let is_commit_referenced = |view: &View, commit_id: &CommitId| -> bool {
+            view.wc_commit_ids()
+                .iter()
+                .filter(|&(ws_id, _)| ws_id != workspace_id)
+                .map(|(_, wc_id)| wc_id)
+                .chain(
+                    view.local_branches()
+                        .flat_map(|(_, target)| target.added_ids()),
+                )
+                .any(|id| id == commit_id)
+        };
 
         let maybe_wc_commit_id = self
             .view
@@ -1341,11 +1348,12 @@ impl MutableRepo {
             if wc_commit.is_discardable(self)?
                 && self
                     .view
-                    .with_ref(|v| local_branch_target_ids(v).all(|id| id != wc_commit.id()))
+                    .with_ref(|v| !is_commit_referenced(v, wc_commit.id()))
                 && self.view().heads().contains(wc_commit.id())
             {
-                // Abandon the working-copy commit we're leaving if it's empty, not pointed by
-                // local branch, and a head commit.
+                // Abandon the working-copy commit we're leaving if it's
+                // discardable, not pointed by local branch or other working
+                // copies, and a head commit.
                 self.record_abandoned_commit(wc_commit_id);
             }
         }

lib/tests/test_mut_repo.rs

@@ -216,6 +216,38 @@ fn test_edit_previous_empty_with_local_branch() {
     assert!(mut_repo.view().heads().contains(old_wc_commit.id()));
 }
 
+#[test]
+fn test_edit_previous_empty_with_other_workspace() {
+    // Test that MutableRepo::edit() does not abandon the previous commit if it
+    // is pointed by another workspace
+    let settings = testutils::user_settings();
+    let test_repo = TestRepo::init();
+    let repo = &test_repo.repo;
+
+    let mut tx = repo.start_transaction(&settings);
+    let mut_repo = tx.mut_repo();
+    let old_wc_commit = mut_repo
+        .new_commit(
+            &settings,
+            vec![repo.store().root_commit_id().clone()],
+            repo.store().empty_merged_tree_id(),
+        )
+        .write()
+        .unwrap();
+    let ws_id = WorkspaceId::default();
+    mut_repo.edit(ws_id.clone(), &old_wc_commit).unwrap();
+    let other_ws_id = WorkspaceId::new("other".to_string());
+    mut_repo.edit(other_ws_id.clone(), &old_wc_commit).unwrap();
+    let repo = tx.commit("test");
+
+    let mut tx = repo.start_transaction(&settings);
+    let mut_repo = tx.mut_repo();
+    let new_wc_commit = write_random_commit(mut_repo, &settings);
+    mut_repo.edit(ws_id, &new_wc_commit).unwrap();
+    mut_repo.rebase_descendants(&settings).unwrap();
+    assert!(mut_repo.view().heads().contains(old_wc_commit.id()));
+}
+
 #[test]
 fn test_edit_previous_empty_non_head() {
     // Test that MutableRepo::edit() does not abandon the previous commit if it