Add reorder_extern_crates and reorder_extern_crates_in_group config options

src/config.rs

@@ -558,6 +558,8 @@ create_config! {
                                             exceeds `chain_one_line_max`";
     imports_indent: IndentStyle, IndentStyle::Visual, "Indent of imports";
     imports_layout: ListTactic, ListTactic::Mixed, "Item layout inside a import block";
+    reorder_extern_crates: bool, true, "Reorder extern crate statements alphabetically";
+    reorder_extern_crates_in_group: bool, true, "Reorder extern crate statements in group";
     reorder_imports: bool, false, "Reorder import statements alphabetically";
     reorder_imports_in_group: bool, false, "Reorder import statements in group";
     reorder_imported_names: bool, true,

src/imports.rs

@@ -113,11 +113,14 @@ fn compare_view_paths(a: &ast::ViewPath_, b: &ast::ViewPath_) -> Ordering {
     }
 }
 
-fn compare_use_items(a: &ast::Item, b: &ast::Item) -> Option<Ordering> {
+fn compare_use_items(context: &RewriteContext, a: &ast::Item, b: &ast::Item) -> Option<Ordering> {
     match (&a.node, &b.node) {
         (&ast::ItemKind::Use(ref a_vp), &ast::ItemKind::Use(ref b_vp)) => {
             Some(compare_view_paths(&a_vp.node, &b_vp.node))
         }
+        (&ast::ItemKind::ExternCrate(..), &ast::ItemKind::ExternCrate(..)) => {
+            Some(context.snippet(a.span).cmp(&context.snippet(b.span)))
+        }
         _ => None,
     }
 }
@@ -214,7 +217,9 @@ impl<'a> FmtVisitor<'a> {
             .collect::<Vec<_>>();
         let pos_after_last_use_item = last_pos_of_prev_use_item;
         // Order the imports by view-path & other import path properties
-        ordered_use_items.sort_by(|a, b| compare_use_items(a.0, b.0).unwrap());
+        ordered_use_items.sort_by(|a, b| {
+            compare_use_items(&self.get_context(), a.0, b.0).unwrap()
+        });
         // First, output the span before the first import
         let prev_span_str = self.snippet(utils::mk_sp(self.last_pos, pos_before_first_use_item));
         // Look for purely trailing space at the start of the prefix snippet before a linefeed, or

src/visitor.rs

@@ -36,6 +36,13 @@ fn is_use_item(item: &ast::Item) -> bool {
     }
 }
 
+fn is_extern_crate(item: &ast::Item) -> bool {
+    match item.node {
+        ast::ItemKind::ExternCrate(..) => true,
+        _ => false,
+    }
+}
+
 pub struct FmtVisitor<'a> {
     pub parse_session: &'a ParseSess,
     pub codemap: &'a CodeMap,
@@ -627,19 +634,20 @@ impl<'a> FmtVisitor<'a> {
         false
     }
 
-    fn walk_mod_items(&mut self, m: &ast::Mod) {
-        let mut items_left: &[ptr::P<ast::Item>] = &m.items;
-        while !items_left.is_empty() {
-            // If the next item is a `use` declaration, then extract it and any subsequent `use`s
-            // to be potentially reordered within `format_imports`. Otherwise, just format the
-            // next item for output.
-            if self.config.reorder_imports() && is_use_item(&*items_left[0]) {
-                let reorder_imports_in_group = self.config.reorder_imports_in_group();
+    fn reorder_items<F>(
+        &mut self,
+        items_left: &[ptr::P<ast::Item>],
+        is_item: &F,
+        in_group: bool,
+    ) -> usize
+    where
+        F: Fn(&ast::Item) -> bool,
+    {
         let mut last = self.codemap.lookup_line_range(items_left[0].span());
-                let use_item_length = items_left
+        let item_length = items_left
             .iter()
             .take_while(|ppi| {
-                        is_use_item(&***ppi) && (!reorder_imports_in_group || {
+                is_item(&***ppi) && (!in_group || {
                     let current = self.codemap.lookup_line_range(ppi.span());
                     let in_same_group = current.lo < last.hi + 2;
                     last = current;
@@ -647,20 +655,44 @@ impl<'a> FmtVisitor<'a> {
                 })
             })
             .count();
-                let (use_items, rest) = items_left.split_at(use_item_length);
+        let items = &items_left[..item_length];
 
-                let at_least_one_in_file_lines = use_items
+        let at_least_one_in_file_lines = items
             .iter()
             .any(|item| !out_of_file_lines_range!(self, item.span));
 
         if at_least_one_in_file_lines {
-                    self.format_imports(use_items);
+            self.format_imports(items);
         } else {
-                    for item in use_items {
+            for item in items {
                 self.push_rewrite(item.span, None);
             }
         }
 
+        item_length
+    }
+
+    fn walk_mod_items(&mut self, m: &ast::Mod) {
+        let mut items_left: &[ptr::P<ast::Item>] = &m.items;
+        while !items_left.is_empty() {
+            // If the next item is a `use` declaration, then extract it and any subsequent `use`s
+            // to be potentially reordered within `format_imports`. Otherwise, just format the
+            // next item for output.
+            if self.config.reorder_imports() && is_use_item(&*items_left[0]) {
+                let used_items_len = self.reorder_items(
+                    &items_left,
+                    &is_use_item,
+                    self.config.reorder_imports_in_group(),
+                );
+                let (_, rest) = items_left.split_at(used_items_len);
+                items_left = rest;
+            } else if self.config.reorder_extern_crates() && is_extern_crate(&*items_left[0]) {
+                let used_items_len = self.reorder_items(
+                    &items_left,
+                    &is_extern_crate,
+                    self.config.reorder_extern_crates_in_group(),
+                );
+                let (_, rest) = items_left.split_at(used_items_len);
                 items_left = rest;
             } else {
                 // `unwrap()` is safe here because we know `items_left`