Fix pairwise drag dragging beyond form boundaries

The pairwise drag implementation would collect all nodes marker as a
pair within the local node tree.

This means that pairs found and other levels in the tree were considered
for dragging and would allow eroneously dragging pairs outside of form 
boundaries.

This fixes the issue by first filtering the matches nodes by those
contained within the current form.

lua/nvim-paredit/treesitter/pairs.lua

@@ -1,4 +1,5 @@
 local ts_utils = require("nvim-paredit.treesitter.utils")
+local ts_forms = require("nvim-paredit.treesitter.forms")
 
 local M = {}
 
@@ -9,6 +10,10 @@ local M = {}
 -- matched nodes.
 function M.find_pairwise_nodes(target_node, opts)
   local root_node = ts_utils.find_local_root(target_node)
+  local enclosing_form = ts_forms.find_nearest_form(target_node, opts)
+  if not enclosing_form then
+    return
+  end
 
   local bufnr = vim.api.nvim_get_current_buf()
   local lang = vim.treesitter.language.get_lang(vim.bo.filetype)
@@ -27,9 +32,11 @@ function M.find_pairwise_nodes(target_node, opts)
   for id, node in captures do
     if query.captures[id] == "pair" then
       if not ts_utils.node_is_comment(node, opts) then
-        table.insert(pairwise_nodes, node)
-        if node:equal(target_node) then
-          found = true
+        if node:parent():equal(enclosing_form) then
+          table.insert(pairwise_nodes, node)
+          if node:equal(target_node) then
+            found = true
+          end
         end
       end
     end

tests/nvim-paredit/pair_drag_spec.lua

@@ -47,6 +47,20 @@ describe("pair dragging ::", function()
       })
     end)
 
+    it("should stop dragging at pair boundaries", function()
+      prepare_buffer({
+        "{:entity {|:a 1 :b 2}}",
+      })
+      paredit.drag_element_backwards({
+        dragging = {
+          auto_drag_pairs = true,
+        },
+      })
+      expect({
+        "{:entity {|:a 1 :b 2}}",
+      })
+    end)
+
     it("should detect various types", function()
       expect_all(function()
         paredit.drag_element_forwards({ dragging = { auto_drag_pairs = true } })