cli: make jj status not just care about the first parent

It seems like I forgot to update the `jj status` output when I decided
(years ago?) that the changes in a commit should always be compared to
the auto-merged parents. I was very confused before I realized that
`jj status` was showing the diff summary against the first parent. I
suppose the fact that `jj status` lists only one parent should have
been a hint. Thanks to ilyagr@ for finding this odd behavior. This
patch fixes it by making the command list all parents, and changes the
diff summary to be against the auto-merged parents.

CHANGELOG.md

@@ -110,6 +110,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   are now better at adding Git refs to prevent that.
   [#815](https://github.com/martinvonz/jj/issues/815)
 
+* When the working-copy commit was a merge, `jj status` would list only the
+  first parent, and the diff summary would be against that parent. The output
+  now lists all parents and the diff summary is against the auto-merged parents.
+
 ### Contributors
 
 Thanks to the people who made this release happen!

src/commands.rs

@@ -1953,16 +1953,18 @@ fn cmd_status(
     let mut formatter = ui.stdout_formatter();
     let formatter = formatter.as_mut();
     if let Some(wc_commit) = &maybe_checkout {
-        formatter.write_str("Parent commit: ")?;
         let workspace_id = workspace_command.workspace_id();
-        write_commit_summary(
-            formatter,
-            repo.as_repo_ref(),
-            &workspace_id,
-            &wc_commit.parents()[0],
-            ui.settings(),
-        )?;
-        formatter.write_str("\n")?;
+        for parent in wc_commit.parents() {
+            formatter.write_str("Parent commit: ")?;
+            write_commit_summary(
+                formatter,
+                repo.as_repo_ref(),
+                &workspace_id,
+                &parent,
+                ui.settings(),
+            )?;
+            formatter.write_str("\n")?;
+        }
         formatter.write_str("Working copy : ")?;
         write_commit_summary(
             formatter,
@@ -2023,7 +2025,7 @@ fn cmd_status(
     }
 
     if let Some(wc_commit) = &maybe_checkout {
-        let parent_tree = wc_commit.parents()[0].tree();
+        let parent_tree = merge_commit_trees(repo.as_repo_ref(), &wc_commit.parents());
         let tree = wc_commit.tree();
         if tree.id() == parent_tree.id() {
             formatter.write_str("The working copy is clean\n")?;

tests/test_resolve_command.rs

@@ -92,6 +92,7 @@ fn test_resolution() {
     insta::assert_snapshot!(test_env.jj_cmd_success(&repo_path, &["status"]), 
     @r###"
     Parent commit: 77c5ed9eda54 a
+    Parent commit: 7c4a3488ba53 b
     Working copy : 665f83829a6a conflict
     Working copy changes:
     M file
@@ -188,6 +189,7 @@ conflict
     insta::assert_snapshot!(test_env.jj_cmd_success(&repo_path, &["status"]), 
     @r###"
     Parent commit: 77c5ed9eda54 a
+    Parent commit: 7c4a3488ba53 b
     Working copy : cbd3d65d2612 conflict
     Working copy changes:
     M file
@@ -232,6 +234,7 @@ conflict
     insta::assert_snapshot!(test_env.jj_cmd_success(&repo_path, &["status"]), 
     @r###"
     Parent commit: 77c5ed9eda54 a
+    Parent commit: 7c4a3488ba53 b
     Working copy : d5b735448648 conflict
     Working copy changes:
     M file

tests/test_status_command.rs

@@ -0,0 +1,41 @@
+// Copyright 2022 The Jujutsu Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use common::TestEnvironment;
+
+pub mod common;
+
+#[test]
+fn test_status_merge() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    std::fs::write(repo_path.join("file"), "base").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["new", "-m=left"]);
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "left"]);
+    test_env.jj_cmd_success(&repo_path, &["new", "@-", "-m=right"]);
+    std::fs::write(repo_path.join("file"), "right").unwrap();
+    test_env.jj_cmd_success(&repo_path, &["new", "left", "@"]);
+
+    // The output should mention each parent, and the diff should be empty (compared
+    // to the auto-merged parents)
+    let stdout = test_env.jj_cmd_success(&repo_path, &["status"]);
+    insta::assert_snapshot!(stdout, @r###"
+    Parent commit: c4097d2ac7c9 left
+    Parent commit: 481d94cd6e34 right
+    Working copy : 92fb36a0639c (no description set)
+    The working copy is clean
+    "###);
+}