treesitter: add string parser (#13008)

runtime/lua/vim/treesitter.lua

@@ -21,7 +21,9 @@ function Parser:parse()
     return self.tree
   end
   local changes
-  self.tree, changes = self._parser:parse_buf(self.bufnr)
+
+  self.tree, changes = self._parser:parse(self:input_source())
+
   self.valid = true
 
   if not vim.tbl_isempty(changes) then
@@ -33,6 +35,10 @@ function Parser:parse()
   return self.tree, changes
 end
 
+function Parser:input_source()
+  return self.bufnr or self.str
+end
+
 function Parser:_on_bytes(bufnr, changed_tick,
                           start_row, start_col, start_byte,
                           old_row, old_col, old_byte,
@@ -152,4 +158,18 @@ function M.get_parser(bufnr, lang, buf_attach_cbs)
   return parsers[id]
 end
 
+function M.get_string_parser(str, lang)
+  vim.validate {
+    str = { str, 'string' },
+    lang = { lang, 'string' }
+  }
+  language.require_language(lang)
+
+  local self = setmetatable({str=str, lang=lang, valid=false}, Parser)
+  self._parser = vim._create_ts_parser(lang)
+  self:parse()
+
+  return self
+end
+
 return M