Sort by path before outputting directory diff so that the order is al…

…ways the same (#593)

* Sort by path before outputting directory diff so that the order is always the same

* Added feature flag --sort-paths (DFT_SORT_PATHS) to enable/disable sorting paths when diffing directory (default disabled)

src/main.rs

@@ -242,6 +242,8 @@ fn main() {
                     options::FileArgument::NamedPath(rhs_path),
                 ) if lhs_path.is_dir() && rhs_path.is_dir() => {
                     let encountered_changes = encountered_changes.clone();
+
+                    // Diffs in parallel when iterating this iterator.
                     let diff_iter = diff_directories(
                         lhs_path,
                         rhs_path,
@@ -263,32 +265,44 @@ fn main() {
 
                         display::json::print_directory(results);
                     } else {
-                        // We want to diff files in the directory in
-                        // parallel, but print the results serially (to
-                        // prevent display interleaving).
-                        // https://github.com/rayon-rs/rayon/issues/210#issuecomment-551319338
-                        let (send, recv) = std::sync::mpsc::sync_channel(1);
-
-                        let encountered_changes = encountered_changes.clone();
-                        let print_options = display_options.clone();
-
-                        let printing_thread = std::thread::spawn(move || {
-                            for diff_result in recv.into_iter() {
-                                print_diff_result(&print_options, &diff_result);
+                        if display_options.sort_paths {
+                            let mut result: Vec<DiffResult> = diff_iter.collect();
+                            result.sort_unstable_by(|a, b| a.display_path.cmp(&b.display_path));
+                            for diff_result in result {
+                                print_diff_result(&display_options, &diff_result);
 
                                 if diff_result.has_reportable_change() {
                                     encountered_changes.store(true, Ordering::Relaxed);
                                 }
                             }
-                        });
+                        } else {
+                            // We want to diff files in the directory in
+                            // parallel, but print the results serially (to
+                            // prevent display interleaving).
+                            // https://github.com/rayon-rs/rayon/issues/210#issuecomment-551319338
+                            let (send, recv) = std::sync::mpsc::sync_channel(1);
+
+                            let encountered_changes = encountered_changes.clone();
+                            let print_options = display_options.clone();
+
+                            let printing_thread = std::thread::spawn(move || {
+                                for diff_result in recv.into_iter() {
+                                    print_diff_result(&print_options, &diff_result);
+
+                                    if diff_result.has_reportable_change() {
+                                        encountered_changes.store(true, Ordering::Relaxed);
+                                    }
+                                }
+                            });
 
-                        diff_iter
-                            .try_for_each_with(send, |s, diff_result| s.send(diff_result))
-                            .expect("Receiver should be connected");
+                            diff_iter
+                                .try_for_each_with(send, |s, diff_result| s.send(diff_result))
+                                .expect("Receiver should be connected");
 
-                        printing_thread
-                            .join()
-                            .expect("Printing thread should not panic");
+                            printing_thread
+                                .join()
+                                .expect("Printing thread should not panic");
+                        }
                     }
                 }
                 _ => {

src/options.rs

@@ -42,6 +42,7 @@ pub(crate) struct DisplayOptions {
     pub(crate) display_width: usize,
     pub(crate) num_context_lines: u32,
     pub(crate) syntax_highlight: bool,
+    pub(crate) sort_paths: bool,
 }
 
 impl Default for DisplayOptions {
@@ -55,6 +56,7 @@ impl Default for DisplayOptions {
             display_width: 80,
             num_context_lines: 3,
             syntax_highlight: true,
+            sort_paths: false,
         }
     }
 }
@@ -287,6 +289,14 @@ When multiple overrides are specified, the first matching override wins."))
                 .hide(true)
                 .allow_invalid_utf8(true),
         )
+        .arg(
+            Arg::new("sort-paths").long("sort-paths")
+                .value_name("on/off")
+                .env("DFT_SORT_PATHS")
+                .possible_values(["on", "off"])
+                .default_value("off")
+                .help("Enable or disable sorting of paths when displaying results of directory diff.")
+        )
         .arg_required_else_help(true)
 }
 
@@ -574,6 +584,8 @@ pub(crate) fn parse_args() -> Mode {
 
     let syntax_highlight = matches.value_of("syntax-highlight") == Some("on");
 
+    let sort_paths = matches.value_of("sort-paths") == Some("on");
+
     let graph_limit = matches
         .value_of("graph-limit")
         .expect("Always present as we've given clap a default")
@@ -667,6 +679,7 @@ pub(crate) fn parse_args() -> Mode {
                 display_width,
                 num_context_lines,
                 syntax_highlight,
+                sort_paths,
             };
 
             let display_path = path.to_string_lossy().to_string();
@@ -703,6 +716,7 @@ pub(crate) fn parse_args() -> Mode {
         display_width,
         num_context_lines,
         syntax_highlight,
+        sort_paths,
     };
 
     Mode::Diff {