merge_tools: process "ui.diff-instructions" option by caller

This gets rid of the last UserSettings dependency from edit_diff_external().
I'm going to remove it from edit_diff() too, and let callers pass a
preconfigured MergeTool struct instead.

These changes will make it easier to add --tool=<name> argument jj-vcs#2575.

cli/src/cli_util.rs

@@ -1746,6 +1746,11 @@ impl WorkspaceCommandTransaction<'_> {
     ) -> Result<MergedTreeId, CommandError> {
         let base_ignores = self.helper.base_ignores()?;
         let settings = &self.helper.settings;
+        let instructions = if settings.diff_instructions() {
+            instructions
+        } else {
+            None
+        };
         Ok(crate::merge_tools::edit_diff(
             ui,
             left_tree,

cli/src/merge_tools/external.rs

@@ -17,7 +17,6 @@ use jj_lib::matchers::Matcher;
 use jj_lib::merge::{Merge, MergedTreeValue};
 use jj_lib::merged_tree::{MergedTree, MergedTreeBuilder};
 use jj_lib::repo_path::{RepoPath, RepoPathBuf};
-use jj_lib::settings::UserSettings;
 use jj_lib::store::Store;
 use jj_lib::working_copy::{CheckoutError, SnapshotOptions};
 use pollster::FutureExt;
@@ -429,7 +428,6 @@ pub fn edit_diff_external(
     matcher: &dyn Matcher,
     instructions: Option<&str>,
     base_ignores: Arc<GitIgnoreFile>,
-    settings: &UserSettings,
 ) -> Result<MergedTreeId, DiffEditError> {
     let got_output_field = find_all_variables(&editor.edit_args).contains(&"output");
     let store = left_tree.store();
@@ -452,8 +450,7 @@ pub fn edit_diff_external(
     let instructions_path_to_cleanup = output_wc_path.join("JJ-INSTRUCTIONS");
     // In the unlikely event that the file already exists, then the user will simply
     // not get any instructions.
-    let add_instructions = if settings.diff_instructions() && !instructions_path_to_cleanup.exists()
-    {
+    let add_instructions = if !instructions_path_to_cleanup.exists() {
         instructions
     } else {
         None

cli/src/merge_tools/mod.rs

@@ -150,7 +150,6 @@ pub fn edit_diff(
             matcher,
             instructions,
             base_ignores,
-            settings,
         ),
     }
 }

cli/tests/test_diffedit_command.rs

@@ -47,6 +47,22 @@ fn test_diffedit() {
     M file2
     "###);
 
+    // Try again with ui.diff-instructions=false
+    std::fs::write(&edit_script, "files-before file1 file2\0files-after file2").unwrap();
+    let (stdout, stderr) = test_env.jj_cmd_ok(
+        &repo_path,
+        &["diffedit", "--config-toml=ui.diff-instructions=false"],
+    );
+    insta::assert_snapshot!(stdout, @"");
+    insta::assert_snapshot!(stderr, @r###"
+    Nothing changed.
+    "###);
+    let stdout = test_env.jj_cmd_success(&repo_path, &["diff", "-s"]);
+    insta::assert_snapshot!(stdout, @r###"
+    D file1
+    M file2
+    "###);
+
     // Nothing happens if the diff-editor exits with an error
     std::fs::write(&edit_script, "rm file2\0fail").unwrap();
     insta::assert_snapshot!(&test_env.jj_cmd_failure(&repo_path, &["diffedit"]), @r###"
@@ -64,8 +80,8 @@ fn test_diffedit() {
     let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["diffedit"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
-    Created kkmpptxz 1930da4a (no description set)
-    Working copy now at: kkmpptxz 1930da4a (no description set)
+    Created kkmpptxz ae84b067 (no description set)
+    Working copy now at: kkmpptxz ae84b067 (no description set)
     Parent commit      : rlvkpnrz 613028a4 (no description set)
     Added 0 files, modified 1 files, removed 0 files
     "###);
@@ -80,10 +96,10 @@ fn test_diffedit() {
     let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["diffedit", "-r", "@-"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
-    Created rlvkpnrz c03ae967 (no description set)
+    Created rlvkpnrz 51a4f74c (no description set)
     Rebased 1 descendant commits
-    Working copy now at: kkmpptxz 2a4dc204 (no description set)
-    Parent commit      : rlvkpnrz c03ae967 (no description set)
+    Working copy now at: kkmpptxz 574af856 (no description set)
+    Parent commit      : rlvkpnrz 51a4f74c (no description set)
     Added 0 files, modified 1 files, removed 0 files
     "###);
     let contents = String::from_utf8(std::fs::read(repo_path.join("file3")).unwrap()).unwrap();
@@ -101,8 +117,8 @@ fn test_diffedit() {
     let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["diffedit", "--from", "@--"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
-    Created kkmpptxz 15f2c966 (no description set)
-    Working copy now at: kkmpptxz 15f2c966 (no description set)
+    Created kkmpptxz cd638328 (no description set)
+    Working copy now at: kkmpptxz cd638328 (no description set)
     Parent commit      : rlvkpnrz 613028a4 (no description set)
     Added 0 files, modified 0 files, removed 1 files
     "###);