diff --git a/cli/src/commands/rebase.rs b/cli/src/commands/rebase.rs
index 8b6ffc68cd..58547e58cc 100644
--- a/cli/src/commands/rebase.rs
+++ b/cli/src/commands/rebase.rs
@@ -20,7 +20,6 @@ use std::sync::Arc;
 use clap::ArgGroup;
 use indexmap::IndexSet;
 use itertools::Itertools;
-use jj_lib::backend::CommitId;
 use jj_lib::commit::{Commit, CommitIteratorExt};
 use jj_lib::object_id::ObjectId;
 use jj_lib::repo::{ReadonlyRepo, Repo};
@@ -356,96 +355,45 @@ fn rebase_revision(
     new_parents: &[Commit],
     rev_arg: &RevisionArg,
 ) -> Result<(), CommandError> {
-    let old_commit = workspace_command.resolve_single_rev(rev_arg)?;
-    workspace_command.check_rewritable([old_commit.id()])?;
-    if new_parents.contains(&old_commit) {
+    let to_rebase_commit = workspace_command.resolve_single_rev(rev_arg)?;
+    workspace_command.check_rewritable([to_rebase_commit.id()])?;
+    if new_parents.contains(&to_rebase_commit) {
         return Err(user_error(format!(
             "Cannot rebase {} onto itself",
-            short_commit_hash(old_commit.id()),
+            short_commit_hash(to_rebase_commit.id()),
         )));
     }
 
-    let children_expression = RevsetExpression::commit(old_commit.id().clone()).children();
-    let child_commits: Vec<_> = children_expression
-        .evaluate_programmatic(workspace_command.repo().as_ref())
-        .unwrap()
-        .iter()
-        .commits(workspace_command.repo().store())
-        .try_collect()?;
-    // Currently, immutable commits are defined so that a child of a rewriteable
-    // commit is always rewriteable.
-    debug_assert!(workspace_command
-        .check_rewritable(child_commits.iter().ids())
-        .is_ok());
-
-    // First, rebase the children of `old_commit`.
     let mut tx = workspace_command.start_transaction();
     let mut rebased_commit_ids = HashMap::new();
-    for child_commit in child_commits {
-        let new_child_parent_ids: Vec<CommitId> = child_commit
-            .parents()
-            .iter()
-            .flat_map(|c| {
-                if c == &old_commit {
-                    old_commit.parent_ids().to_vec()
-                } else {
-                    [c.id().clone()].to_vec()
-                }
-            })
-            .collect();
-
-        // Some of the new parents may be ancestors of others as in
-        // `test_rebase_single_revision`.
-        let new_child_parents_expression = RevsetExpression::commits(new_child_parent_ids.clone())
-            .minus(
-                &RevsetExpression::commits(new_child_parent_ids.clone())
-                    .parents()
-                    .ancestors(),
-            );
-        let new_child_parents = new_child_parents_expression
-            .evaluate_programmatic(tx.base_repo().as_ref())
-            .unwrap()
-            .iter()
-            .collect_vec();
 
-        rebased_commit_ids.insert(
-            child_commit.id().clone(),
-            rebase_commit(settings, tx.mut_repo(), child_commit, new_child_parents)?
-                .id()
-                .clone(),
-        );
-    }
-    // Now, rebase the descendants of the children.
+    // First, rebase the descendants of `to_rebase_commit`.
     // TODO(ilyagr): Consider making it possible for these descendants to become
     // emptied, like --skip_empty. This would require writing careful tests.
-    rebased_commit_ids.extend(tx.mut_repo().rebase_descendants_return_map(settings)?);
+    tx.mut_repo().transform_descendants(
+        settings,
+        vec![to_rebase_commit.id().clone()],
+        |mut rewriter| {
+            let old_commit = rewriter.old_commit();
+            let old_commit_id = old_commit.id().clone();
+
+            // Replace references to `to_rebase_commit` with its parents.
+            rewriter.replace_parent(to_rebase_commit.id(), to_rebase_commit.parent_ids());
+            if rewriter.parents_changed() {
+                let builder = rewriter.rebase(settings)?;
+                let commit = builder.write()?;
+                rebased_commit_ids.insert(old_commit_id, commit.id().clone());
+            }
+            Ok(())
+        },
+    )?;
+
     let num_rebased_descendants = rebased_commit_ids.len();
 
     // We now update `new_parents` to account for the rebase of all of
-    // `old_commit`'s descendants. Even if some of the original `new_parents`
-    // were descendants of `old_commit`, this will no longer be the case after
+    // `to_rebase_commit`'s descendants. Even if some of the original `new_parents`
+    // were descendants of `to_rebase_commit`, this will no longer be the case after
     // the update.
-    //
-    // To make the update simpler, we assume that each commit was rewritten only
-    // once; we don't have a situation where both `(A,B)` and `(B,C)` are in
-    // `rebased_commit_ids`.
-    //
-    // TODO(BUG #2650): There is something wrong with this assumption, the next TODO
-    // seems to be a little optimistic. See the panicked test in
-    // `test_rebase_with_child_and_descendant_bug_2600`.
-    //
-    // TODO(ilyagr): This assumption relies on the fact that, after
-    // `rebase_descendants`, a descendant of `old_commit` cannot also be a
-    // direct child of `old_commit`. This fact will likely change, see
-    // https://github.com/martinvonz/jj/issues/2600. So, the code needs to be
-    // updated before that happens. This would also affect
-    // `test_rebase_with_child_and_descendant_bug_2600`.
-    //
-    // The issue is that if a child and a descendant of `old_commit` were the
-    // same commit (call it `Q`), it would be rebased first by `rebase_commit`
-    // above, and then the result would be rebased again by
-    // `rebase_descendants_return_map`. Then, if we were trying to rebase
-    // `old_commit` onto `Q`, new_parents would only account for one of these.
     let new_parents = new_parents
         .iter()
         .map(|new_parent| {
@@ -456,20 +404,20 @@ fn rebase_revision(
         })
         .collect();
 
-    let tx_description = format!("rebase commit {}", old_commit.id().hex());
-    // Finally, it's safe to rebase `old_commit`. We can skip rebasing if it is
-    // already a child of `new_parents`. Otherwise, at this point, it should no
-    // longer have any children; they have all been rebased and the originals
+    let tx_description = format!("rebase commit {}", to_rebase_commit.id().hex());
+    // Finally, it's safe to rebase `to_rebase_commit`. We can skip rebasing if it
+    // is already a child of `new_parents`. Otherwise, at this point, it should
+    // no longer have any children; they have all been rebased and the originals
     // have been abandoned.
-    let skipped_commit_rebase = if old_commit.parent_ids() == new_parents {
+    let skipped_commit_rebase = if to_rebase_commit.parent_ids() == new_parents {
         if let Some(mut formatter) = ui.status_formatter() {
             write!(formatter, "Skipping rebase of commit ")?;
-            tx.write_commit_summary(formatter.as_mut(), &old_commit)?;
+            tx.write_commit_summary(formatter.as_mut(), &to_rebase_commit)?;
             writeln!(formatter)?;
         }
         true
     } else {
-        rebase_commit(settings, tx.mut_repo(), old_commit, new_parents)?;
+        rebase_commit(settings, tx.mut_repo(), to_rebase_commit, new_parents)?;
         debug_assert_eq!(tx.mut_repo().rebase_descendants(settings)?, 0);
         false
     };
diff --git a/cli/tests/common/mod.rs b/cli/tests/common/mod.rs
index 880046ee61..72f4eb5a51 100644
--- a/cli/tests/common/mod.rs
+++ b/cli/tests/common/mod.rs
@@ -227,6 +227,7 @@ impl TestEnvironment {
     /// Run a `jj` command, check that it failed with code 101, and return its
     /// stderr
     #[must_use]
+    #[allow(dead_code)]
     pub fn jj_cmd_panic(&self, current_dir: &Path, args: &[&str]) -> String {
         let assert = self.jj_cmd(current_dir, args).assert().code(101).stdout("");
         self.normalize_output(&get_stderr_string(&assert))
diff --git a/cli/tests/test_rebase_command.rs b/cli/tests/test_rebase_command.rs
index 0dd41d2919..f137983db5 100644
--- a/cli/tests/test_rebase_command.rs
+++ b/cli/tests/test_rebase_command.rs
@@ -266,63 +266,64 @@ fn test_rebase_single_revision() {
     let repo_path = test_env.env_root().join("repo");
 
     create_commit(&test_env, &repo_path, "a", &[]);
-    create_commit(&test_env, &repo_path, "b", &[]);
-    create_commit(&test_env, &repo_path, "c", &["a", "b"]);
-    create_commit(&test_env, &repo_path, "d", &["c"]);
+    create_commit(&test_env, &repo_path, "b", &["a"]);
+    create_commit(&test_env, &repo_path, "c", &["a"]);
+    create_commit(&test_env, &repo_path, "d", &["b", "c"]);
+    create_commit(&test_env, &repo_path, "e", &["d"]);
     // Test the setup
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
-    @  d
-    ◉    c
+    @  e
+    ◉    d
     ├─╮
-    │ ◉  b
-    ◉ │  a
+    │ ◉  c
+    ◉ │  b
     ├─╯
+    ◉  a
     ◉
     "###);
 
-    // Descendants of the rebased commit "b" should be rebased onto parents. First
-    // we test with a non-merge commit. Normally, the descendant "c" would still
-    // have 2 parents afterwards: the parent of "b" -- the root commit -- and
-    // "a". However, since the root commit is an ancestor of "a", we don't
-    // actually want both to be parents of the same commit. So, only "a" becomes
-    // a parent.
-    let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["rebase", "-r", "b", "-d", "a"]);
+    // Descendants of the rebased commit "c" should be rebased onto parents. First
+    // we test with a non-merge commit.
+    let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["rebase", "-r", "c", "-d", "b"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Also rebased 2 descendant commits onto parent of rebased commit
-    Working copy now at: vruxwmqv 7e15b97a d | d
-    Parent commit      : royxmykx 934236c8 c | c
+    Working copy now at: znkkpsqq 2668ffbe e | e
+    Parent commit      : vruxwmqv 7b370c85 d | d
     Added 0 files, modified 0 files, removed 1 files
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
-    ◉  b
-    │ @  d
-    │ ◉  c
+    ◉  c
+    │ @  e
+    │ ◉  d
+    ╭─┤
+    ◉ │  b
     ├─╯
     ◉  a
     ◉
     "###);
     test_env.jj_cmd_ok(&repo_path, &["undo"]);
 
-    // Now, let's try moving the merge commit. After, both parents of "c" ("a" and
-    // "b") should become parents of "d".
-    let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["rebase", "-r", "c", "-d", "root()"]);
+    // Now, let's try moving the merge commit. After, both parents of "d" ("b" and
+    // "c") should become parents of "e".
+    let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["rebase", "-r", "d", "-d", "a"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Also rebased 1 descendant commits onto parent of rebased commit
-    Working copy now at: vruxwmqv bf87078f d | d
-    Parent commit      : zsuskuln d370aee1 b | b
-    Parent commit      : rlvkpnrz 2443ea76 a | a
+    Working copy now at: znkkpsqq ed210c15 e | e
+    Parent commit      : zsuskuln 1394f625 b | b
+    Parent commit      : royxmykx c0cb3a0b c | c
     Added 0 files, modified 0 files, removed 1 files
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
-    ◉  c
-    │ @    d
+    ◉  d
+    │ @    e
     │ ├─╮
-    │ │ ◉  a
+    │ │ ◉  c
     ├───╯
     │ ◉  b
     ├─╯
+    ◉  a
     ◉
     "###);
 }
@@ -354,17 +355,17 @@ fn test_rebase_single_revision_merge_parent() {
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Also rebased 1 descendant commits onto parent of rebased commit
-    Working copy now at: vruxwmqv c62d0789 d | d
-    Parent commit      : zsuskuln d370aee1 b | b
+    Working copy now at: vruxwmqv a37531e8 d | d
     Parent commit      : rlvkpnrz 2443ea76 a | a
+    Parent commit      : zsuskuln d370aee1 b | b
     Added 0 files, modified 0 files, removed 1 files
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
     ◉  c
     │ @  d
     ╭─┤
-    ◉ │  a
     │ ◉  b
+    ◉ │  a
     ├─╯
     ◉
     "###);
@@ -694,7 +695,8 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     test_env.jj_cmd_ok(test_env.env_root(), &["init", "repo", "--git"]);
     let repo_path = test_env.env_root().join("repo");
 
-    create_commit(&test_env, &repo_path, "base", &[]);
+    create_commit(&test_env, &repo_path, "notroot", &[]);
+    create_commit(&test_env, &repo_path, "base", &["notroot"]);
     create_commit(&test_env, &repo_path, "a", &["base"]);
     create_commit(&test_env, &repo_path, "b", &["base", "a"]);
     create_commit(&test_env, &repo_path, "c", &["b"]);
@@ -708,16 +710,17 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     │ ◉  a
     ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
     // ===================== rebase -s tests =================
     let (stdout, stderr) =
-        test_env.jj_cmd_ok(&repo_path, &["rebase", "-s", "base", "-d", "root()"]);
+        test_env.jj_cmd_ok(&repo_path, &["rebase", "-s", "base", "-d", "notroot"]);
     insta::assert_snapshot!(stdout, @"");
     // This should be a no-op
     insta::assert_snapshot!(stderr, @r###"
-    Skipping rebase of commit rlvkpnrz 0c61db1b base | base
+    Skipping rebase of commit zsuskuln 0a7fb8f6 base | base
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
     @  c
@@ -726,6 +729,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     │ ◉  a
     ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
@@ -734,7 +738,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     insta::assert_snapshot!(stdout, @"");
     // This should be a no-op
     insta::assert_snapshot!(stderr, @r###"
-    Skipping rebase of commit zsuskuln 2c5b7858 a | a
+    Skipping rebase of commit royxmykx 86a06598 a | a
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
     @  c
@@ -743,6 +747,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     │ ◉  a
     ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
@@ -751,8 +756,8 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Rebased 3 commits
-    Working copy now at: vruxwmqv 2b10f149 c | c
-    Parent commit      : royxmykx 3b233bd8 b | b
+    Working copy now at: znkkpsqq cf8ecff5 c | c
+    Parent commit      : vruxwmqv 24e1a270 b | b
     "###);
     // Commit "a" should be rebased onto the root commit. Commit "b" should have
     // "base" and "a" as parents as before.
@@ -762,6 +767,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     ├─╮
     │ ◉  a
     ◉ │  base
+    ◉ │  notroot
     ├─╯
     ◉
     "###);
@@ -776,6 +782,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     │ ◉  a
     ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
@@ -784,7 +791,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     // The commits in roots(base..c), i.e. commit "a" should be rebased onto "base",
     // which is a no-op
     insta::assert_snapshot!(stderr, @r###"
-    Skipping rebase of commit zsuskuln 2c5b7858 a | a
+    Skipping rebase of commit royxmykx 86a06598 a | a
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
     @  c
@@ -793,6 +800,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     │ ◉  a
     ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
@@ -801,8 +809,8 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Rebased 2 commits
-    Working copy now at: vruxwmqv 2fc4ef73 c | c
-    Parent commit      : royxmykx 9912ef4b b | b
+    Working copy now at: znkkpsqq 76914dcc c | c
+    Parent commit      : vruxwmqv f73f03c7 b | b
     "###);
     // The commits in roots(a..c), i.e. commit "b" should be rebased onto "a",
     // which means "b" loses its "base" parent
@@ -811,6 +819,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     ◉  b
     ◉  a
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
@@ -819,7 +828,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     insta::assert_snapshot!(stdout, @"");
     // This should be a no-op
     insta::assert_snapshot!(stderr, @r###"
-    Skipping rebase of commit rlvkpnrz 0c61db1b base | base
+    Skipping rebase of commit rlvkpnrz 39f28e63 notroot | notroot
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
     @  c
@@ -828,6 +837,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     │ ◉  a
     ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
@@ -841,6 +851,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     │ ◉  a
     ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
@@ -848,134 +859,66 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
         test_env.jj_cmd_ok(&repo_path, &["rebase", "-r", "base", "-d", "root()"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
-    Skipping rebase of commit rlvkpnrz 0c61db1b base | base
-    Rebased 4 descendant commits onto parent of commit
-    Working copy now at: vruxwmqv 57aaa944 c | c
-    Parent commit      : royxmykx c8495a71 b | b
+    Also rebased 3 descendant commits onto parent of rebased commit
+    Working copy now at: znkkpsqq 45371aaf c | c
+    Parent commit      : vruxwmqv c0a76bf4 b | b
     Added 0 files, modified 0 files, removed 1 files
     "###);
     // The user would expect unsimplified ancestry here.
-    // ◉  base
-    // │ @  c
-    // │ ◉    b
-    // │ ├─╮
-    // │ │ ◉  a
-    // │ ├─╯
-    // ├─╯
-    // ◉
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
-    @  c
-    ◉  b
-    ◉  a
-    │ ◉  base
+    ◉  base
+    │ @  c
+    │ ◉    b
+    │ ├─╮
+    │ │ ◉  a
+    │ ├─╯
+    │ ◉  notroot
     ├─╯
     ◉
     "###);
 
-    // TODO(#2650) !!!!! The panic here is a BUG !!!
-    // This tests the algorithm for rebasing onto descendants. The result should be
-    // simplified if and only if it's simplified in the above case.
+    // This tests the algorithm for rebasing onto descendants. The result should
+    // have unsimplified ancestry.
     test_env.jj_cmd_ok(&repo_path, &["op", "restore", &setup_opid]);
-    let stderr = test_env.jj_cmd_panic(&repo_path, &["rebase", "-r", "base", "-d", "b"]);
-    assert!(stderr.contains("graph has cycle"));
-    // // At time of writing:
-    // insta::assert_snapshot!(stderr, @r###"
-    // thread 'main' panicked at lib/src/dag_walk.rs:113:13:
-    // graph has cycle
-    // stack backtrace:
-    //    0: rust_begin_unwind
-    //              at
-    // /rustc/6cf088810f66fff15d05bf7135c5f5888b7c93b4/library/std/src/panicking.rs:
-    // 645:5    1: core::panicking::panic_fmt
-    //              at
-    // /rustc/6cf088810f66fff15d05bf7135c5f5888b7c93b4/library/core/src/panicking.
-    // rs:72:14    2: jj_lib::dag_walk::topo_order_forward_ok
-    //              at
-    // /usr/local/google/home/ilyagr/dev/jj/lib/src/dag_walk.rs:113:13
-    //    3: jj_lib::dag_walk::topo_order_reverse_ok
-    //              at
-    // /usr/local/google/home/ilyagr/dev/jj/lib/src/dag_walk.rs:160:22
-    //    4: jj_lib::dag_walk::topo_order_reverse
-    //              at
-    // /usr/local/google/home/ilyagr/dev/jj/lib/src/dag_walk.rs:142:5
-    //    5: jj_lib::rewrite::DescendantRebaser::new
-    //              at
-    // /usr/local/google/home/ilyagr/dev/jj/lib/src/rewrite.rs:306:24
-    //    6: jj_lib::repo::MutableRepo::create_descendant_rebaser
-    //              at /usr/local/google/home/ilyagr/dev/jj/lib/src/repo.rs:844:9
-    //    7: jj_lib::repo::MutableRepo::rebase_descendants_return_rebaser
-    //              at /usr/local/google/home/ilyagr/dev/jj/lib/src/repo.rs:861:27
-    //    8: jj_lib::repo::MutableRepo::rebase_descendants_with_options
-    //              at /usr/local/google/home/ilyagr/dev/jj/lib/src/repo.rs:872:12
-    //    9: jj_lib::repo::MutableRepo::rebase_descendants
-    //              at /usr/local/google/home/ilyagr/dev/jj/lib/src/repo.rs:878:9
-    //   10: jj_cli::commands::rebase::rebase_revision
-    //              at
-    // /usr/local/google/home/ilyagr/dev/jj/cli/src/commands/rebase.rs:420:22
-    //   11: jj_cli::commands::rebase::cmd_rebase
-    //              at
-    // /usr/local/google/home/ilyagr/dev/jj/cli/src/commands/rebase.rs:197:9
-    //   12: jj_cli::commands::run_command
-    //              at
-    // /usr/local/google/home/ilyagr/dev/jj/cli/src/commands/mod.rs:187:39   13:
-    // core::ops::function::FnOnce::call_once              at
-    // /rustc/6cf088810f66fff15d05bf7135c5f5888b7c93b4/library/core/src/ops/
-    // function.rs:250:5   14: core::ops::function::FnOnce::call_once{{vtable.
-    // shim}}              at
-    // /rustc/6cf088810f66fff15d05bf7135c5f5888b7c93b4/library/core/src/ops/
-    // function.rs:250:5   15: <alloc::boxed::Box<F,A> as
-    // core::ops::function::FnOnce<Args>>::call_once              at
-    // /rustc/6cf088810f66fff15d05bf7135c5f5888b7c93b4/library/alloc/src/boxed.rs:
-    // 2007:9   16: jj_cli::cli_util::CliRunner::run_internal
-    //              at
-    // /usr/local/google/home/ilyagr/dev/jj/cli/src/cli_util.rs:2867:9
-    //   17: jj_cli::cli_util::CliRunner::run
-    //              at
-    // /usr/local/google/home/ilyagr/dev/jj/cli/src/cli_util.rs:2884:22
-    //   18: jj::main
-    //              at /usr/local/google/home/ilyagr/dev/jj/cli/src/main.rs:18:5
-    //   19: core::ops::function::FnOnce::call_once
-    //              at
-    // /rustc/6cf088810f66fff15d05bf7135c5f5888b7c93b4/library/core/src/ops/
-    // function.rs:250:5 note: Some details are omitted, run with
-    // `RUST_BACKTRACE=full` for a verbose backtrace. "###);
-    //
-    // Unsimlified ancestry would look like
-    // @  c
-    // │ ◉  base
-    // ├─╯
-    // ◉    b
-    // ├─╮
-    // │ ◉  a
-    // ├─╯
-    // ◉
+    let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["rebase", "-r", "base", "-d", "b"]);
+    insta::assert_snapshot!(stdout, @"");
+    insta::assert_snapshot!(stderr, @r###"
+    Also rebased 3 descendant commits onto parent of rebased commit
+    Working copy now at: znkkpsqq e28fa972 c | c
+    Parent commit      : vruxwmqv 8d0eeb6a b | b
+    Added 0 files, modified 0 files, removed 1 files
+    "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
-    @  c
+    ◉  base
+    │ @  c
+    ├─╯
     ◉    b
     ├─╮
     │ ◉  a
     ├─╯
-    ◉  base
+    ◉  notroot
     ◉
     "###);
 
-    // This tests the algorithm for rebasing onto descendants. The result should be
-    // simplified if and only if it's simplified in the above case.
+    // This tests the algorithm for rebasing onto descendants. The result should
+    // have unsimplified ancestry.
     test_env.jj_cmd_ok(&repo_path, &["op", "restore", &setup_opid]);
     let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["rebase", "-r", "base", "-d", "a"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
-    Also rebased 4 descendant commits onto parent of rebased commit
-    Working copy now at: vruxwmqv 0b91d0eb c | c
-    Parent commit      : royxmykx fb944989 b | b
+    Also rebased 3 descendant commits onto parent of rebased commit
+    Working copy now at: znkkpsqq a9da974c c | c
+    Parent commit      : vruxwmqv 0072139c b | b
     Added 0 files, modified 0 files, removed 1 files
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
     ◉  base
     │ @  c
     │ ◉  b
+    ╭─┤
+    ◉ │  a
     ├─╯
-    ◉  a
+    ◉  notroot
     ◉
     "###);
 
@@ -988,6 +931,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     │ ◉  a
     ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
@@ -995,8 +939,8 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Also rebased 2 descendant commits onto parent of rebased commit
-    Working copy now at: vruxwmqv f366e099 c | c
-    Parent commit      : royxmykx bfc7c538 b | b
+    Working copy now at: znkkpsqq 7210b05e c | c
+    Parent commit      : vruxwmqv da3f7511 b | b
     Added 0 files, modified 0 files, removed 1 files
     "###);
     // In this case, it is unclear whether the user would always prefer unsimplified
@@ -1006,6 +950,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     │ @  c
     │ ◉  b
     │ ◉  base
+    │ ◉  notroot
     ├─╯
     ◉
     "###);
@@ -1015,44 +960,44 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Also rebased 1 descendant commits onto parent of rebased commit
-    Working copy now at: vruxwmqv 4d1fd267 c | c
-    Parent commit      : zsuskuln 2c5b7858 a | a
+    Working copy now at: znkkpsqq f280545e c | c
+    Parent commit      : zsuskuln 0a7fb8f6 base | base
+    Parent commit      : royxmykx 86a06598 a | a
     Added 0 files, modified 0 files, removed 1 files
     "###);
     // The user would expect unsimplified ancestry here.
-    // ◉  b
-    // │ @  c
-    // │ ├─╮
-    // │ │ ◉  a
-    // │ ├─╯
-    // │ ◉  base
-    // ├─╯
-    // ◉
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
     ◉  b
-    │ @  c
-    │ ◉  a
+    │ @    c
+    │ ├─╮
+    │ │ ◉  a
+    │ ├─╯
     │ ◉  base
+    │ ◉  notroot
     ├─╯
     ◉
     "###);
 
-    // This tests the algorithm for rebasing onto descendants. The result should be
-    // simplified if and only if it's simplified in the above case.
+    // This tests the algorithm for rebasing onto descendants. The result should
+    // have unsimplified ancestry.
     test_env.jj_cmd_ok(&repo_path, &["op", "restore", &setup_opid]);
     let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["rebase", "-r", "b", "-d", "c"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Also rebased 1 descendant commits onto parent of rebased commit
-    Working copy now at: vruxwmqv 0bacac66 c | c
-    Parent commit      : zsuskuln 2c5b7858 a | a
+    Working copy now at: znkkpsqq c0a7cd80 c | c
+    Parent commit      : zsuskuln 0a7fb8f6 base | base
+    Parent commit      : royxmykx 86a06598 a | a
     Added 0 files, modified 0 files, removed 1 files
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
     ◉  b
-    @  c
-    ◉  a
+    @    c
+    ├─╮
+    │ ◉  a
+    ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 
@@ -1062,8 +1007,8 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["rebase", "-r", "c", "-d", "a"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
-    Working copy now at: vruxwmqv e64d4b0d c | c
-    Parent commit      : zsuskuln 2c5b7858 a | a
+    Working copy now at: znkkpsqq 7a3bc050 c | c
+    Parent commit      : royxmykx 86a06598 a | a
     Added 0 files, modified 0 files, removed 1 files
     "###);
     insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
@@ -1073,6 +1018,7 @@ fn test_rebase_with_child_and_descendant_bug_2600() {
     ◉ │  a
     ├─╯
     ◉  base
+    ◉  notroot
     ◉
     "###);
 }