1 files changed, 58 insertions, 0 deletions
diff --git a/lua/nvim-treesitter/query_predicates.lua b/lua/nvim-treesitter/query_predicates.lua
new file mode 100644
index 00000000..00daa50d
--- /dev/null
+++ b/lua/nvim-treesitter/query_predicates.lua
@@ -0,0 +1,58 @@
+local utils = require'nvim-treesitter.utils'
+
+local M = {}
+
+local function get_nth_child(node, n)
+  if node:named_child_count() > n then
+    return node:named_child(n)
+  end
+end
+
+local function get_node(query, match, pred_item)
+  return utils.get_at_path(match, query.captures[pred_item]..'.node')
+end
+
+function M.check_predicate(query, match, pred)
+  local check_function = M[string.gsub('check_'..pred[1], "%?$", '')]
+  if check_function then
+    return check_function(query, match, pred)
+  else
+    return true
+  end
+end
+
+function M.check_negated_predicate(query, match, pred)
+  local check_function = M[string.gsub('check_'..string.sub(pred[1], #"not-" + 1), "%?$", '')]
+  if check_function then
+    return not check_function(query, match, pred)
+  else
+    return true
+  end
+end
+
+function M.check_first(query, match, pred)
+  if #pred ~= 2 then error("first? must have exactly one argument!") end
+  local node = get_node(query, match, pred[2])
+  if node and node:parent() then
+    return get_nth_child(node:parent(), 0) == node
+  end
+end
+
+function M.check_last(query, match, pred)
+  if #pred ~= 2 then error("first? must have exactly one argument!") end
+  local node = get_node(query, match, pred[2])
+  if node and node:parent() then
+    local num_children = node:parent():named_child_count()
+    return get_nth_child(node:parent(), num_children - 1) == node
+  end
+end
+
+function M.check_nth(query, match, pred)
+  if #pred ~= 3 then error("nth? must have exactly two arguments!") end
+  local node = get_node(query, match, pred[2])
+  if node and node:parent() then
+    return get_nth_child(node:parent(), pred[3] - 1) == node
+  end
+end
+
+return M