cli: obslog: show diffs from all predecessors, not first predecessor

Suppose a squash node in obslog is analogous to a merge in revisions log, it
makes sense to show diffs from auto-merge (or auto-squash) parents. This
basically means a non-partial squash node no longer shows diffs.

This also fixes missing diffs at the root predecessors if there were.

CHANGELOG.md

@@ -38,6 +38,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 * `jj --at-op=@` no longer merges concurrent operations if explicitly specified.
 
+* `jj obslog -p` no longer shows diffs at non-partial squash operations.
+  Previously, it showed the same diffs as the second predecessor.
+
 ### Deprecations
 
 * The original configuration syntax for `jj fix` is now deprecated in favor of

cli/src/commands/interdiff.rs

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::slice;
+
 use clap::ArgGroup;
 use jj_lib::rewrite::rebase_to_dest_parent;
 use tracing::instrument;
@@ -53,7 +55,11 @@ pub(crate) fn cmd_interdiff(
         workspace_command.resolve_single_rev(args.from.as_ref().unwrap_or(&RevisionArg::AT))?;
     let to = workspace_command.resolve_single_rev(args.to.as_ref().unwrap_or(&RevisionArg::AT))?;
 
-    let from_tree = rebase_to_dest_parent(workspace_command.repo().as_ref(), &from, &to)?;
+    let from_tree = rebase_to_dest_parent(
+        workspace_command.repo().as_ref(),
+        slice::from_ref(&from),
+        &to,
+    )?;
     let to_tree = to.tree()?;
     let matcher = workspace_command
         .parse_file_patterns(&args.paths)?

cli/src/commands/obslog.rs

@@ -190,12 +190,8 @@ fn show_predecessor_patch(
     commit: &Commit,
     width: usize,
 ) -> Result<(), CommandError> {
-    let mut predecessors = commit.predecessors();
-    let predecessor = match predecessors.next() {
-        Some(predecessor) => predecessor?,
-        None => return Ok(()),
-    };
-    let predecessor_tree = rebase_to_dest_parent(repo, &predecessor, commit)?;
+    let predecessors: Vec<_> = commit.predecessors().try_collect()?;
+    let predecessor_tree = rebase_to_dest_parent(repo, &predecessors, commit)?;
     let tree = commit.tree()?;
     renderer.show_diff(
         ui,

cli/src/commands/operation/diff.rs

@@ -556,8 +556,8 @@ fn show_change_diff(
     width: usize,
 ) -> Result<(), CommandError> {
     match (&*change.removed_commits, &*change.added_commits) {
-        ([predecessor], [commit]) => {
-            let predecessor_tree = rebase_to_dest_parent(repo, predecessor, commit)?;
+        (predecessors @ [_], [commit]) => {
+            let predecessor_tree = rebase_to_dest_parent(repo, predecessors, commit)?;
             let tree = commit.tree()?;
             diff_renderer.show_diff(
                 ui,

cli/tests/test_obslog_command.rs

@@ -234,7 +234,7 @@ fn test_obslog_squash() {
     test_env.jj_cmd_ok(&repo_path, &["new", "-m", "second"]);
     std::fs::write(repo_path.join("file1"), "foo\nbar\n").unwrap();
 
-    // full
+    // not partial
     test_env.jj_cmd_ok(&repo_path, &["squash", "-m", "squashed 1"]);
 
     test_env.jj_cmd_ok(&repo_path, &["describe", "-m", "third"]);
@@ -267,10 +267,6 @@ fn test_obslog_squash() {
     insta::assert_snapshot!(stdout, @r###"
     ○      qpvuntsm [email protected] 2001-02-03 08:05:15 d49749bf
     ├─┬─╮  squashed 3
-    │ │ │  Added regular file file4:
-    │ │ │          1: foo4
-    │ │ │  Added regular file file5:
-    │ │ │          1: foo5
     │ │ ○  vruxwmqv hidden [email protected] 2001-02-03 08:05:15 8f2ae2b5
     │ │ │  fifth
     │ │ │  Added regular file file5:
@@ -285,10 +281,10 @@ fn test_obslog_squash() {
     │    (empty) fourth
     ○    qpvuntsm hidden [email protected] 2001-02-03 08:05:12 1408a0a7
     ├─╮  squashed 2
-    │ │  Modified regular file file1:
-    │ │     1    1: foo
-    │ │     2    2: bar
-    │ │          3: baz
+    │ │  Removed regular file file2:
+    │ │     1     : foo2
+    │ │  Removed regular file file3:
+    │ │     1     : foo3
     │ ○  zsuskuln hidden [email protected] 2001-02-03 08:05:12 c9460789
     │ │  third
     │ │  Modified regular file file1:
@@ -305,9 +301,6 @@ fn test_obslog_squash() {
     │    (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
     │ ○  kkmpptxz hidden [email protected] 2001-02-03 08:05:10 46acd22a
     │ │  second
     │ │  Modified regular file file1:

lib/src/rewrite.rs

@@ -303,20 +303,25 @@ pub fn rebase_commit_with_options(
     }
 }
 
+/// Moves changes from `sources` to the `destination` parent, returns new tree.
 pub fn rebase_to_dest_parent(
     repo: &dyn Repo,
-    source: &Commit,
+    sources: &[Commit],
     destination: &Commit,
 ) -> BackendResult<MergedTree> {
-    if source.parent_ids() == destination.parent_ids() {
-        Ok(source.tree()?)
-    } else {
-        let destination_parent_tree = destination.parent_tree(repo)?;
-        let source_parent_tree = source.parent_tree(repo)?;
-        let source_tree = source.tree()?;
-        let rebased_tree = destination_parent_tree.merge(&source_parent_tree, &source_tree)?;
-        Ok(rebased_tree)
+    if let [source] = sources {
+        if source.parent_ids() == destination.parent_ids() {
+            return source.tree();
+        }
     }
+    sources.iter().try_fold(
+        destination.parent_tree(repo)?,
+        |destination_tree, source| {
+            let source_parent_tree = source.parent_tree(repo)?;
+            let source_tree = source.tree()?;
+            destination_tree.merge(&source_parent_tree, &source_tree)
+        },
+    )
 }
 
 #[derive(Clone, Copy, Default, PartialEq, Eq, Debug)]