feat(picker.diff): native diff now also highlights the language of the diffed code in the diff

lua/snacks/picker/core/preview.lua

@@ -24,6 +24,7 @@ M.__index = M
 
 local ns = vim.api.nvim_create_namespace("snacks.picker.preview")
 local ns_loc = vim.api.nvim_create_namespace("snacks.picker.preview.loc")
+local did_diff_setup = false
 
 -- HACK: work-around for buffer-local window options mess. From the docs:
 -- > When editing a buffer that has been edited before, the options from the window
@@ -281,6 +282,9 @@ function M:highlight(opts)
   end
   self:check_big()
   local lang = Snacks.util.get_lang(opts.lang or ft)
+  if lang == "diff" then
+    self:diff()
+  end
   if not (lang and pcall(vim.treesitter.start, self.win.buf, lang)) and ft then
     vim.bo[self.win.buf].syntax = ft
   end
@@ -411,4 +415,20 @@ function M:notify(msg, level, opts)
   self:highlight({ lang = "lua" })
 end
 
+function M:diff()
+  if did_diff_setup then
+    return
+  end
+  did_diff_setup = true
+  vim.treesitter.query.set(
+    "diff",
+    "injections",
+    [[; extends
+    (block
+      (new_file (filename) @injection.filename)
+      (hunks
+        (hunk changes: (changes) @injection.content
+            (#set! injection.include-children))))]]
+  )
+end
 return M