feat(treesitter): upstream is_parent()

Util from the nvim-treesitter project.
Renamed is_parent to is_ancestor for clarity.

runtime/lua/vim/treesitter.lua

@@ -118,4 +118,27 @@ function M.get_string_parser(str, lang, opts)
   return LanguageTree.new(str, lang, opts)
 end
 
+--- Determines whether a node is the ancestor of another
+---
+---@param dest table the possible ancestor
+---@param source table the possible descendant node
+---
+---@returns (boolean) True if dest is an ancestor of source
+function M.is_ancestor(dest, source)
+  if not (dest and source) then
+    return false
+  end
+
+  local current = source
+  while current ~= nil do
+    if current == dest then
+      return true
+    end
+
+    current = current:parent()
+  end
+
+  return false
+end
+
 return M

test/functional/treesitter/utils_spec.lua

@@ -0,0 +1,29 @@
+local helpers = require('test.functional.helpers')(after_each)
+
+local clear = helpers.clear
+local insert = helpers.insert
+local eq = helpers.eq
+local exec_lua = helpers.exec_lua
+
+before_each(clear)
+
+describe('treesitter utils', function()
+  clear()
+  it('can find an ancestor', function()
+    insert([[
+      int main() {
+        int x = 3;
+      }]])
+
+    exec_lua([[
+      parser = vim.treesitter.get_parser(0, "c")
+      tree = parser:parse()[1]
+      root = tree:root()
+      ancestor = root:child(0)
+      child = ancestor:child(0)
+    ]])
+
+    eq(true, exec_lua('return vim.treesitter.is_ancestor(ancestor, child)'))
+    eq(false, exec_lua('return vim.treesitter.is_ancestor(child, ancestor)'))
+  end)
+end)