squash: fix -A -B behavior

and add the corresponding test. The children of the new commit were not
properly rebased on their parents.

fix: #7636

CHANGELOG.md

@@ -30,6 +30,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 * `jj metaedit --author-timestamp` twice with the same value no longer
 edits the change twice in some cases.
 
+* `jj squash`: fixed improper revision rebase when both `--insert-after` and
+  `--insert-before` were used.
+
 ## [0.34.0] - 2025-10-01
 
 ### Release highlights

cli/src/commands/squash.rs

@@ -13,6 +13,7 @@
 // limitations under the License.
 
 use std::collections::HashMap;
+use std::iter::once;
 
 use clap_complete::ArgValueCandidates;
 use clap_complete::ArgValueCompleter;
@@ -273,11 +274,21 @@ pub(crate) fn cmd_squash(
             .write()?;
         let mut rewritten = HashMap::new();
         tx.repo_mut()
-            .transform_descendants(child_ids, async |mut rewriter| {
+            .transform_descendants(child_ids.clone(), async |mut rewriter| {
                 let old_commit_id = rewriter.old_commit().id().clone();
                 for parent_id in &parent_ids {
                     rewriter.replace_parent(parent_id, [commit.id()]);
                 }
+                let new_parents = rewriter.new_parents();
+                if child_ids.contains(&old_commit_id) && !new_parents.contains(commit.id()) {
+                    rewriter.set_new_parents(
+                        new_parents
+                            .iter()
+                            .cloned()
+                            .chain(once(commit.id().clone()))
+                            .collect(),
+                    );
+                }
                 let new_commit = rewriter.rebase().await?.write()?;
                 rewritten.insert(old_commit_id, new_commit);
                 num_rebased += 1;

cli/tests/test_squash_command.rs

@@ -2211,6 +2211,41 @@ fn test_squash_to_new_commit() {
        -- operation a8bb9104802c new empty commit
     [EOF]
     ");
+
+    // --before and --after together
+    work_dir.run_jj(["op", "restore", &setup_opid]).success();
+    let output = work_dir.run_jj([
+        "squash",
+        "-m",
+        "file 3&4",
+        "-f",
+        "kkmpptxzrspx::",
+        "--insert-after",
+        "root()",
+        "--insert-before",
+        "rlvkpnrzqnoo",
+    ]);
+    insta::assert_snapshot!(output, @r"
+    ------- stderr -------
+    Created new commit pyoswmwk d5aa6638 file 3&4
+    Rebased 1 descendant commits
+    Working copy  (@) now at: yqnpwwmq 68513612 (empty) (no description set)
+    Parent commit (@-)      : rlvkpnrz ed79225c file2
+    [EOF]
+    ");
+
+    insta::assert_snapshot!(get_log_with_summary(&work_dir), @r"
+    @  yqnpwwmqtwyk
+    ○    rlvkpnrzqnoo file2
+    ├─╮  A file2
+    │ ○  pyoswmwkkqyt file 3&4
+    │ │  A file3
+    │ │  A file4
+    ○ │  qpvuntsmwlqt file1
+    ├─╯  A file1
+    ◆  zzzzzzzzzzzz
+    [EOF]
+    ");
 }
 
 #[must_use]