diff: extract inter-diff helper

This isn't as primitive as show_diff() or show_patch(), but there are three
callers. Let's add a helper method to remove repo argument.

cli/src/commands/evolog.rs

@@ -16,8 +16,6 @@ use itertools::Itertools;
 use jj_lib::commit::Commit;
 use jj_lib::dag_walk::topo_order_reverse_ok;
 use jj_lib::matchers::EverythingMatcher;
-use jj_lib::repo::Repo;
-use jj_lib::rewrite::rebase_to_dest_parent;
 use tracing::instrument;
 
 use super::log::get_node_template;
@@ -80,7 +78,6 @@ pub(crate) fn cmd_evolog(
     args: &EvologArgs,
 ) -> Result<(), CommandError> {
     let workspace_command = command.workspace_helper(ui)?;
-    let repo = workspace_command.repo().as_ref();
 
     let start_commit = workspace_command.resolve_single_rev(&args.revision)?;
 
@@ -164,7 +161,7 @@ pub(crate) fn cmd_evolog(
             if let Some(renderer) = &diff_renderer {
                 let mut formatter = ui.new_formatter(&mut buffer);
                 let width = usize::saturating_sub(ui.term_width(), graph_width());
-                show_predecessor_patch(ui, repo, renderer, formatter.as_mut(), &commit, width)?;
+                show_predecessor_patch(ui, renderer, formatter.as_mut(), &commit, width)?;
             }
             let node_symbol = format_template(ui, &Some(commit.clone()), &node_template);
             graph.add_node(
@@ -180,7 +177,7 @@ pub(crate) fn cmd_evolog(
                 .write(formatter, |formatter| template.format(&commit, formatter))?;
             if let Some(renderer) = &diff_renderer {
                 let width = ui.term_width();
-                show_predecessor_patch(ui, repo, renderer, formatter, &commit, width)?;
+                show_predecessor_patch(ui, renderer, formatter, &commit, width)?;
             }
         }
     }
@@ -190,22 +187,18 @@ pub(crate) fn cmd_evolog(
 
 fn show_predecessor_patch(
     ui: &Ui,
-    repo: &dyn Repo,
     renderer: &DiffRenderer,
     formatter: &mut dyn Formatter,
     commit: &Commit,
     width: usize,
 ) -> Result<(), CommandError> {
     let predecessors: Vec<_> = commit.predecessors().try_collect()?;
-    let predecessor_tree = rebase_to_dest_parent(repo, &predecessors, commit)?;
+    renderer.show_inter_diff(
-    let tree = commit.tree()?;
-    renderer.show_diff(
         ui,
         formatter,
-        &predecessor_tree,
+        &predecessors,
-        &tree,
+        &commit,
         &EverythingMatcher,
-        &Default::default(),
         width,
     )?;
     Ok(())

cli/src/commands/interdiff.rs

@@ -15,7 +15,6 @@
 use std::slice;
 
 use clap::ArgGroup;
-use jj_lib::rewrite::rebase_to_dest_parent;
 use tracing::instrument;
 
 use crate::cli_util::CommandHelper;
@@ -55,25 +54,17 @@ pub(crate) fn cmd_interdiff(
     let from =
         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(),
-        slice::from_ref(&from),
-        &to,
-    )?;
-    let to_tree = to.tree()?;
     let matcher = workspace_command
         .parse_file_patterns(&args.paths)?
         .to_matcher();
     let diff_renderer = workspace_command.diff_renderer_for(&args.format)?;
     ui.request_pager();
-    diff_renderer.show_diff(
+    diff_renderer.show_inter_diff(
         ui,
         ui.stdout_formatter().as_mut(),
-        &from_tree,
+        slice::from_ref(&from),
-        &to_tree,
+        &to,
         matcher.as_ref(),
-        &Default::default(),
         ui.term_width(),
     )?;
     Ok(())

cli/src/commands/operation/diff.rs

@@ -34,7 +34,6 @@ use jj_lib::repo::ReadonlyRepo;
 use jj_lib::repo::Repo;
 use jj_lib::revset;
 use jj_lib::revset::RevsetIteratorExt as _;
-use jj_lib::rewrite::rebase_to_dest_parent;
 
 use crate::cli_util::short_change_hash;
 use crate::cli_util::short_operation_hash;
@@ -260,7 +259,6 @@ pub fn show_op_diff(
                     show_change_diff(
                         ui,
                         formatter.as_mut(),
-                        current_repo,
                         diff_renderer,
                         modified_change,
                         width,
@@ -287,14 +285,7 @@ pub fn show_op_diff(
                 )?;
                 if let Some(diff_renderer) = &diff_renderer {
                     let width = ui.term_width();
-                    show_change_diff(
+                    show_change_diff(ui, formatter, diff_renderer, modified_change, width)?;
-                        ui,
-                        formatter,
-                        current_repo,
-                        diff_renderer,
-                        modified_change,
-                        width,
-                    )?;
                 }
             }
         }
@@ -563,7 +554,6 @@ fn compute_operation_commits_diff(
 fn show_change_diff(
     ui: &Ui,
     formatter: &mut dyn Formatter,
-    repo: &dyn Repo,
     diff_renderer: &DiffRenderer,
     change: &ModifiedChange,
     width: usize,
@@ -572,15 +562,12 @@ fn show_change_diff(
         (predecessors @ ([] | [_]), [commit]) => {
             // New or modified change. If the modification involved a rebase,
             // show diffs from the rebased tree.
-            let predecessor_tree = rebase_to_dest_parent(repo, predecessors, commit)?;
+            diff_renderer.show_inter_diff(
-            let tree = commit.tree()?;
-            diff_renderer.show_diff(
                 ui,
                 formatter,
-                &predecessor_tree,
+                predecessors,
-                &tree,
+                commit,
                 &EverythingMatcher,
-                &Default::default(),
                 width,
             )?;
         }

cli/src/diff_util.rs

@@ -51,6 +51,7 @@ use jj_lib::object_id::ObjectId;
 use jj_lib::repo::Repo;
 use jj_lib::repo_path::RepoPath;
 use jj_lib::repo_path::RepoPathUiConverter;
+use jj_lib::rewrite::rebase_to_dest_parent;
 use jj_lib::settings::ConfigResultExt as _;
 use jj_lib::settings::UserSettings;
 use jj_lib::store::Store;
@@ -357,6 +358,32 @@ impl<'a> DiffRenderer<'a> {
         Ok(())
     }
 
+    /// Generates diff between `from_commits` and `to_commit` based off their
+    /// parents. The `from_commits` will temporarily be rebased onto the
+    /// `to_commit` parents to exclude unrelated changes.
+    pub fn show_inter_diff(
+        &self,
+        ui: &Ui,
+        formatter: &mut dyn Formatter,
+        from_commits: &[Commit],
+        to_commit: &Commit,
+        matcher: &dyn Matcher,
+        width: usize,
+    ) -> Result<(), DiffRenderError> {
+        let from_tree = rebase_to_dest_parent(self.repo, from_commits, to_commit)?;
+        let to_tree = to_commit.tree()?;
+        let copy_records = CopyRecords::default(); // TODO
+        self.show_diff(
+            ui,
+            formatter,
+            &from_tree,
+            &to_tree,
+            matcher,
+            &copy_records,
+            width,
+        )
+    }
+
     /// Generates diff of the given `commit` compared to its parents.
     pub fn show_patch(
         &self,