feat: extension sorter (#1181)

doc/nvim-tree-lua.txt

@@ -244,7 +244,7 @@ if the tree was previously open.
 
 *nvim-tree.sort_by*
 Changes how files within the same directory are sorted.
-Can be one of 'name', 'case_sensitive' or 'modification_time'.
+Can be one of 'name', 'case_sensitive', 'modification_time' or 'extension'.
   Type: `string`, Default: `"name"`
 
 *nvim-tree.hijack_unnamed_buffer_when_opening*

lua/nvim-tree/explorer/sorters.lua

@@ -124,12 +124,38 @@ function M.node_comparator_modification_time(a, b)
   return last_modified_b <= last_modified_a
 end
 
+function M.node_comparator_extension(a, b)
+  if not (a and b) then
+    return true
+  end
+
+  if a.nodes and not b.nodes then
+    return true
+  elseif not a.nodes and b.nodes then
+    return false
+  end
+
+  if not (a.extension and b.extension) then
+    return true
+  end
+
+  if a.extension and not b.extension then
+    return true
+  elseif not a.extension and b.extension then
+    return false
+  end
+
+  return a.extension:lower() <= b.extension:lower()
+end
+
 function M.setup(opts)
   M.sort_by = opts.sort_by
   if M.sort_by == "modification_time" then
     M.node_comparator = M.node_comparator_modification_time
   elseif M.sort_by == "case_sensitive" then
     M.node_comparator = M.node_comparator_name_case_sensisive
+  elseif M.sort_by == "extension" then
+    M.node_comparator = M.node_comparator_extension
   else
     M.node_comparator = M.node_comparator_name_ignorecase
   end