merge tools: split DiffEditWorkingCopies from DiffWorkingCopies

As suggested by @yuja in https://github.com/martinvonz/jj/pull/3296#discussion_r1525829712

cli/src/merge_tools/diff_working_copies.rs

@@ -36,7 +36,6 @@ pub(crate) struct DiffWorkingCopies {
     left_tree_state: TreeState,
     right_tree_state: TreeState,
     output_tree_state: Option<TreeState>,
-    instructions_path_to_cleanup: Option<PathBuf>,
 }
 
 impl DiffWorkingCopies {
@@ -177,21 +176,26 @@ pub(crate) fn check_out_trees(
         left_tree_state,
         right_tree_state,
         output_tree_state,
-        instructions_path_to_cleanup: None,
     })
 }
 
-/// Checks out the trees, populates JJ_INSTRUCTIONS, and makes appropriate sides
-/// readonly.
-pub fn check_out_trees_for_diffedit(
+pub(crate) struct DiffEditWorkingCopies {
+    pub working_copies: DiffWorkingCopies,
+    instructions_path_to_cleanup: Option<PathBuf>,
+}
+
+impl DiffEditWorkingCopies {
+    /// Checks out the trees, populates JJ_INSTRUCTIONS, and makes appropriate
+    /// sides readonly.
+    pub fn check_out(
         store: &Arc<Store>,
         left_tree: &MergedTree,
         right_tree: &MergedTree,
         matcher: &dyn Matcher,
         output_is: Option<DiffSide>,
         instructions: Option<&str>,
-) -> Result<DiffWorkingCopies, DiffEditError> {
-    let mut diff_wc = check_out_trees(store, left_tree, right_tree, matcher, output_is)?;
+    ) -> Result<Self, DiffEditError> {
+        let diff_wc = check_out_trees(store, left_tree, right_tree, matcher, output_is)?;
         let got_output_field = output_is.is_some();
 
         set_readonly_recursively(diff_wc.left_working_copy_path())
@@ -252,20 +256,23 @@ diff editing in mind and be a little inaccurate.
             output_instructions_file
                 .write_all(instructions.as_bytes())
                 .map_err(ExternalToolError::SetUpDir)?;
-        diff_wc.instructions_path_to_cleanup = Some(output_instructions_path);
+        };
+
+        Ok(Self {
+            working_copies: diff_wc,
+            instructions_path_to_cleanup: add_instructions.map(|_| output_instructions_path),
+        })
     }
 
-    Ok(diff_wc)
-}
-
-pub fn snapshot_diffedit_results(
-    diff_wc: DiffWorkingCopies,
+    pub fn snapshot_results(
+        self,
         base_ignores: Arc<GitIgnoreFile>,
     ) -> Result<MergedTreeId, DiffEditError> {
-    if let Some(path) = diff_wc.instructions_path_to_cleanup {
+        if let Some(path) = self.instructions_path_to_cleanup {
             std::fs::remove_file(path).ok();
         }
 
+        let diff_wc = self.working_copies;
         // Snapshot changes in the temporary output directory.
         let mut output_tree_state = diff_wc
             .output_tree_state
@@ -278,3 +285,4 @@ pub fn snapshot_diffedit_results(
         })?;
         Ok(output_tree_state.current_tree_id().clone())
     }
+}

cli/src/merge_tools/external.rs

@@ -16,8 +16,7 @@ use regex::{Captures, Regex};
 use thiserror::Error;
 
 use super::diff_working_copies::{
-    check_out_trees, check_out_trees_for_diffedit, new_utf8_temp_dir, set_readonly_recursively,
-    snapshot_diffedit_results, DiffSide,
+    check_out_trees, new_utf8_temp_dir, set_readonly_recursively, DiffEditWorkingCopies, DiffSide,
 };
 use super::{ConflictResolveError, DiffEditError, DiffGenerateError};
 use crate::config::CommandNameAndArgs;
@@ -261,7 +260,7 @@ pub fn edit_diff_external(
 ) -> Result<MergedTreeId, DiffEditError> {
     let got_output_field = find_all_variables(&editor.edit_args).contains(&"output");
     let store = left_tree.store();
-    let diff_wc = check_out_trees_for_diffedit(
+    let diffedit_wc = DiffEditWorkingCopies::check_out(
         store,
         left_tree,
         right_tree,
@@ -270,7 +269,7 @@ pub fn edit_diff_external(
         instructions,
     )?;
 
-    let patterns = diff_wc.to_command_variables();
+    let patterns = diffedit_wc.working_copies.to_command_variables();
     let mut cmd = Command::new(&editor.program);
     cmd.args(interpolate_variables(&editor.edit_args, &patterns));
     tracing::info!(?cmd, "Invoking the external diff editor:");
@@ -286,7 +285,7 @@ pub fn edit_diff_external(
         }));
     }
 
-    snapshot_diffedit_results(diff_wc, base_ignores)
+    diffedit_wc.snapshot_results(base_ignores)
 }
 
 /// Generates textual diff by the specified `tool`, and writes into `writer`.