cli: commit, split: pass temporary commit object to description helper

cli/src/commands/commit.rs

@@ -89,8 +89,7 @@ new working-copy commit.
         matcher.as_ref(),
         format_instructions,
     )?;
-    let middle_tree = tx.repo().store().get_root_tree(&tree_id)?;
-    if !args.paths.is_empty() && middle_tree.id() == base_tree.id() {
+    if !args.paths.is_empty() && tree_id == base_tree.id() {
         writeln!(
             ui.warning_default(),
             "The given paths do not match any file: {}",
@@ -107,19 +106,17 @@ new working-copy commit.
         commit_builder.set_author(commit_builder.committer().clone());
     }
 
-    let template = description_template_for_commit(
-        ui,
-        command.settings(),
-        tx.base_workspace_helper(),
-        "",
-        commit.description(),
-        &base_tree,
-        &middle_tree,
-    )?;
-
     let description = if !args.message_paragraphs.is_empty() {
         join_message_paragraphs(&args.message_paragraphs)
     } else {
+        let temp_commit = commit_builder.write_hidden()?;
+        let template = description_template_for_commit(
+            ui,
+            command.settings(),
+            tx.base_workspace_helper(),
+            "",
+            &temp_commit,
+        )?;
         edit_description(tx.base_repo(), &template, command.settings())?
     };
     commit_builder.set_description(description);

cli/src/commands/split.rs

@@ -128,14 +128,13 @@ the operation will be aborted.
             .rewrite_commit(command.settings(), &commit)
             .detach();
         commit_builder.set_tree_id(selected_tree_id);
+        let temp_commit = commit_builder.write_hidden()?;
         let template = description_template_for_commit(
             ui,
             command.settings(),
             tx.base_workspace_helper(),
             "Enter a description for the first commit.",
-            commit.description(),
-            &base_tree,
-            &selected_tree,
+            &temp_commit,
         )?;
         let description = edit_description(tx.base_repo(), &template, command.settings())?;
         commit_builder.set_description(description);
@@ -145,13 +144,13 @@ the operation will be aborted.
     // Create the second commit, which includes everything the user didn't
     // select.
     let second_commit = {
-        let (new_tree, base_tree) = if args.parallel {
+        let new_tree = if args.parallel {
             // Merge the original commit tree with its parent using the tree
             // containing the user selected changes as the base for the merge.
             // This results in a tree with the changes the user didn't select.
-            (end_tree.merge(&selected_tree, &base_tree)?, &base_tree)
+            end_tree.merge(&selected_tree, &base_tree)?
         } else {
-            (end_tree, &selected_tree)
+            end_tree
         };
         let parents = if args.parallel {
             commit.parent_ids().to_vec()
@@ -173,14 +172,13 @@ the operation will be aborted.
             // second commit.
             "".to_string()
         } else {
+            let temp_commit = commit_builder.write_hidden()?;
             let template = description_template_for_commit(
                 ui,
                 command.settings(),
                 tx.base_workspace_helper(),
                 "Enter a description for the second commit.",
-                commit.description(),
-                base_tree,
-                &new_tree,
+                &temp_commit,
             )?;
             edit_description(tx.base_repo(), &template, command.settings())?
         };

cli/src/description_util.rs

@@ -1,7 +1,6 @@
 use itertools::Itertools;
 use jj_lib::commit::Commit;
 use jj_lib::matchers::EverythingMatcher;
-use jj_lib::merged_tree::MergedTree;
 use jj_lib::repo::ReadonlyRepo;
 use jj_lib::settings::UserSettings;
 
@@ -116,27 +115,24 @@ pub fn description_template_for_commit(
     settings: &UserSettings,
     workspace_command: &WorkspaceCommandHelper,
     intro: &str,
-    overall_commit_description: &str,
-    from_tree: &MergedTree,
-    to_tree: &MergedTree,
+    commit: &Commit,
 ) -> Result<String, CommandError> {
     let mut diff_summary_bytes = Vec::new();
     let diff_renderer = workspace_command.diff_renderer(vec![DiffFormat::Summary]);
-    diff_renderer.show_diff(
+    diff_renderer.show_patch(
         ui,
         &mut PlainTextFormatter::new(&mut diff_summary_bytes),
-        from_tree,
-        to_tree,
+        commit,
         &EverythingMatcher,
     )?;
     let mut template_chunks = Vec::new();
     if !intro.is_empty() {
         template_chunks.push(format!("JJ: {intro}\n"));
     }
-    template_chunks.push(if overall_commit_description.is_empty() {
+    template_chunks.push(if commit.description().is_empty() {
         settings.default_description()
     } else {
-        overall_commit_description.to_owned()
+        commit.description().to_owned()
     });
     if !diff_summary_bytes.is_empty() {
         template_chunks.push("\n".to_owned());