obslog: reverse order of predecessors in topo traversal

cli/src/commands/obslog.rs

@@ -113,7 +113,21 @@ pub(crate) fn cmd_obslog(
     let mut commits = topo_order_reverse_ok(
         vec![Ok(start_commit)],
         |commit: &Commit| commit.id().clone(),
-        |commit: &Commit| commit.predecessors().collect_vec(),
+        |commit: &Commit| {
+            let mut predecessors = commit.predecessors().collect_vec();
+            // Predecessors don't need to follow any defined order. However in
+            // practice, if there are multiple predecessors, then usually the
+            // first predecessor is the previous version of the same change, and
+            // the other predecessors are commits that were squashed into it. If
+            // multiple commits are squashed at once, then they are usually
+            // recorded in chronological order. We want to show squashed commits
+            // in reverse chronological order, and we also want to show squashed
+            // commits before the squash destination (since the destination's
+            // subgraph may contain earlier squashed commits as well), so we
+            // visit the predecessors in reverse order.
+            predecessors.reverse();
+            predecessors
+        },
     )?;
     if args.deprecated_limit.is_some() {
         writeln!(

cli/tests/test_obslog_command.rs

@@ -235,31 +235,53 @@ fn test_obslog_squash() {
     std::fs::write(repo_path.join("file1"), "foo\nbar\n").unwrap();
 
     let edit_script = test_env.set_up_fake_editor();
-    std::fs::write(edit_script, "write\nsquashed").unwrap();
+    std::fs::write(&edit_script, "write\nsquashed 1").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["squash"]);
+
+    test_env.jj_cmd_ok(&repo_path, &["describe", "-m", "third"]);
+    std::fs::write(repo_path.join("file1"), "foo\nbar\nbaz\n").unwrap();
+
+    std::fs::write(&edit_script, "write\nsquashed 2").unwrap();
     test_env.jj_cmd_ok(&repo_path, &["squash"]);
 
     let stdout = test_env.jj_cmd_success(&repo_path, &["obslog", "-p", "-r", "@-"]);
     insta::assert_snapshot!(stdout, @r###"
-    ◉    qpvuntsm [email protected] 2001-02-03 08:05:10 68647e34
-    ├─╮  squashed
+    ◉    qpvuntsm [email protected] 2001-02-03 08:05:12 1408a0a7
+    ├─╮  squashed 2
+    │ │  Modified regular file file1:
+    │ │     1    1: foo
+    │ │     2    2: bar
+    │ │          3: baz
+    │ ◉  zsuskuln hidden [email protected] 2001-02-03 08:05:12 7015a42c
+    │ │  third
+    │ │  Modified regular file file1:
+    │ │     1    1: foo
+    │ │     2    2: bar
+    │ │          3: baz
+    │ ◉  zsuskuln hidden [email protected] 2001-02-03 08:05:11 66645763
+    │ │  (empty) third
+    │ ◉  zsuskuln hidden [email protected] 2001-02-03 08:05:10 1c7afcb4
+    │    (empty) (no description set)
+    ◉    qpvuntsm hidden [email protected] 2001-02-03 08:05:10 e3c2a446
+    ├─╮  squashed 1
     │ │  Modified regular file file1:
     │ │     1    1: foo
     │ │          2: bar
-    ◉ │  qpvuntsm hidden [email protected] 2001-02-03 08:05:09 766420db
-    │ │  first
-    │ │  Added regular file file1:
-    │ │          1: foo
-    ◉ │  qpvuntsm hidden [email protected] 2001-02-03 08:05:08 fa15625b
-    │ │  (empty) first
-    ◉ │  qpvuntsm hidden [email protected] 2001-02-03 08:05:07 230dd059
-      │  (empty) (no description set)
-      ◉  kkmpptxz hidden [email protected] 2001-02-03 08:05:10 46acd22a
-      │  second
-      │  Modified regular file file1:
-      │     1    1: foo
-      │          2: bar
-      ◉  kkmpptxz hidden [email protected] 2001-02-03 08:05:09 cba41deb
-         (empty) second
+    │ ◉  kkmpptxz hidden [email protected] 2001-02-03 08:05:10 46acd22a
+    │ │  second
+    │ │  Modified regular file file1:
+    │ │     1    1: foo
+    │ │          2: bar
+    │ ◉  kkmpptxz hidden [email protected] 2001-02-03 08:05:09 cba41deb
+    │    (empty) second
+    ◉  qpvuntsm hidden [email protected] 2001-02-03 08:05:09 766420db
+    │  first
+    │  Added regular file file1:
+    │          1: foo
+    ◉  qpvuntsm hidden [email protected] 2001-02-03 08:05:08 fa15625b
+    │  (empty) first
+    ◉  qpvuntsm hidden [email protected] 2001-02-03 08:05:07 230dd059
+       (empty) (no description set)
     "###);
 }
 

cli/tests/test_squash_command.rs

@@ -972,10 +972,10 @@ fn test_squash_from_multiple_partial_no_op() {
     insta::assert_snapshot!(stdout, @r###"
     @    e178068add8c d
     ├─╮
-    ◉ │  b37ca1ee3306 d
-    ◉ │  1d9eb34614c9 d
-      ◉  b73077b08c59 b
-      ◉  a786561e909f b
+    │ ◉  b73077b08c59 b
+    │ ◉  a786561e909f b
+    ◉  b37ca1ee3306 d
+    ◉  1d9eb34614c9 d
     "###);
 
     // If no source commits match the paths, then the whole operation is a no-op