Add predicates module

2 files changed, 70 insertions, 1 deletions

diff --git a/lua/nvim-treesitter/query.lua b/lua/nvim-treesitter/query.lua
index 896b11dad..678c7b683 100644
--- a/lua/nvim-treesitter/query.lua
+++ b/lua/nvim-treesitter/query.lua
@@ -2,6 +2,7 @@ local api = vim.api
 local ts = vim.treesitter
 local utils = require'nvim-treesitter.utils'
 local parsers = require'nvim-treesitter.parsers'
+local predicates = require'nvim-treesitter.query_predicates'
 
 local M = {}
 
@@ -129,7 +130,7 @@ function M.iter_prepared_matches(query, qnode, bufnr, start_row, end_row)
 
   local matches = query:iter_matches(qnode, bufnr, start_row, end_row)
 
-  return function()
+  local function iterator()
     local pattern, match = matches()
     if pattern ~= nil then
       local prepared_match = {}
@@ -147,15 +148,25 @@ function M.iter_prepared_matches(query, qnode, bufnr, start_row, end_row)
       local preds = query.info.patterns[pattern]
       if preds then
         for _, pred in pairs(preds) do
+          -- functions
           if pred[1] == "set!" and type(pred[2]) == "string" then
             insert_to_path(prepared_match, split(pred[2]), pred[3])
           end
+
+          -- predicates
+          if type(pred[1]) == 'string' then
+            if not predicates.check_predicate(query, prepared_match, pred) or
+               not predicates.check_negated_predicate(query, prepared_match, pred) then
+              return iterator()
+            end
+          end
         end
       end
 
       return prepared_match
     end
   end
+  return iterator
 end
 
 --- Return all nodes corresponding to a specific capture path (like @definition.var, @reference.type)
diff --git a/lua/nvim-treesitter/query_predicates.lua b/lua/nvim-treesitter/query_predicates.lua
new file mode 100644
index 000000000..00daa50d3
--- /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