feat: add sort_by "filetype"

doc/nvim-tree-lua.txt

@@ -568,15 +568,16 @@ Reloads the explorer every time a buffer is written to.
 
 *nvim-tree.sort_by*
 Changes how files within the same directory are sorted.
-Can be one of `name`, `case_sensitive`, `modification_time`, `extension` or a
-function.
+Can be one of `name`, `case_sensitive`, `modification_time`, `extension`,
+`filetype` or a function.
   Type: `string` | `function(nodes)`, Default: `"name"`
 
   Function may perform a sort or return a string with one of the above
   methods. It is passed a table of nodes to be sorted, each node containing:
   - `absolute_path`: `string`
   - `executable`:    `boolean`
   - `extension`:     `string`
+  - `filetype`:      `string`
   - `link_to`:       `string`
   - `name`:          `string`
   - `type`:          `"directory"` | `"file"` | `"link"`

lua/nvim-tree/explorer/sorters.lua

@@ -80,6 +80,7 @@ function M.sort(t)
         absolute_path = n.absolute_path,
         executable = n.executable,
         extension = n.extension,
+        filetype = vim.filetype.match { filename = n.name },
         link_to = n.link_to,
         name = n.name,
         type = n.type,
@@ -191,6 +192,32 @@ function C.extension(a, b)
   return a.extension:lower() <= b.extension:lower()
 end
 
+function C.filetype(a, b)
+  local a_ft = vim.filetype.match { filename = a.name }
+  local b_ft = vim.filetype.match { filename = b.name }
+
+  -- directories first
+  if a.nodes and not b.nodes then
+    return true
+  elseif not a.nodes and b.nodes then
+    return false
+  end
+
+  -- one is nil, the other wins
+  if a_ft and not b_ft then
+    return true
+  elseif not a_ft and b_ft then
+    return false
+  end
+
+  -- same filetype or both nil, sort by name
+  if a_ft == b_ft then
+    return C.name(a, b)
+  end
+
+  return a_ft < b_ft
+end
+
 function M.setup(opts)
   M.config = {}
   M.config.sort_by = opts.sort_by