feat(refactor.navigation): allow a fallback_function for goto_definition

`fallback_function` is called when nvim-treesitter can not resolve the
variable under the cursor.

README.md

@@ -184,9 +184,10 @@ EOF
 ## Refactor: navigation
 
 Provides "go to definition" for the symbol under the cursor,
-and lists the definitions from the current file.
-goto_next_usage/goto_previous_usage go to the next usage of the
-identifier under the cursor.
+and lists the definitions from the current file. If you use
+`goto_definition_lsp_fallback` instead of `goto_definition` in the config below 
+`vim.lsp.buf.definition` is used if nvim-treesitter can not resolve the variable.
+`goto_next_usage`/`goto_previous_usage` go to the next usage of the identifier under the cursor.
 
 
 ```lua

doc/nvim-treesitter.txt

@@ -244,6 +244,11 @@ Supported options:
 - keymaps:
   - goto_definition: go to the definition of the symbol under the cursor.
     Defaults to `gnd`.
+  - goto_definition_lsp_fallback: go to the definition of the symbol under
+    the cursor or use vim.lsp.buf.definition if the symbol can not be
+    resolved. You can use your own fallback function if create a mapping for
+    `lua require'nvim-treesitter.refactor.navigation(nil, fallback_function)<cr>` .
+    No default mapping
   - list_definitions: list all definitions from the current file.
     Defaults to `gnD`.
   - goto_next_usage: go to next usage of identifier under the cursor.

lua/nvim-treesitter/refactor/navigation.lua

@@ -8,16 +8,23 @@ local api = vim.api
 
 local M = {}
 
-function M.goto_definition(bufnr)
+function M.goto_definition(bufnr, fallback_function)
   local bufnr = bufnr or api.nvim_get_current_buf()
   local node_at_point = ts_utils.get_node_at_cursor()
 
   if not node_at_point then return end
 
-  local definition, _ = locals.find_definition(node_at_point, bufnr)
-  ts_utils.goto_node(definition)
+  local definition = locals.find_definition(node_at_point, bufnr)
+
+  if fallback_function and definition.id == node_at_point.id then
+    fallback_function()
+  else
+    ts_utils.goto_node(definition)
+  end
 end
 
+function M.goto_definition_lsp_fallback(bufnr) M.goto_definition(bufnr, vim.lsp.buf.definition) end
+
 function M.list_definitions(bufnr)
   local bufnr = bufnr or api.nvim_get_current_buf()
   local definitions = locals.get_definitions(bufnr)
@@ -57,7 +64,6 @@ function M.goto_adjacent_usage(bufnr, delta)
 
   local target_index = (index + delta + #usages - 1) % #usages + 1
   ts_utils.goto_node(usages[target_index])
-  return usages[target_index]
 end
 
 function M.goto_next_usage(bufnr) return M.goto_adjacent_usage(bufnr, 1) end