Implement pairwise element dragging

This adds two new APIs - `drag_pair_forwards` and its companion
`drag_pair_backwards` which allow dragging 'pairs' of elements within a
form.

An easy example is the key-value pairs within a map which typically are
meant to stay together when reordering.

This can, however, be used for any form. This means if you have some
vector containing logical pairs (because of the actual semantics of your
code) you can use a dedicated keybinding to drag them around together.

This change also introduces a new config option at:

`dragging.auto_drag_pairs = true|false`

which will alter the behaviour of the existing `drag_element_forwards`
and `drag_element_backwards` APIs in order to try infer whether they are
contained within a node that is made up of pairs.

For example if this setting is `true` and a `drag_element_forwards` is
used on the keys of a map then they will be dragged pairwise.

This new config option defaults to `true` under the assumption that this
is generally the desired behaviour.

README.md

@@ -65,6 +65,13 @@ paredit.setup({
   --              this case it will place the cursor on the moved edge
   cursor_behaviour = "auto", -- remain, follow, auto
 
+  dragging = {
+    -- If set to `true` paredit will attempt to infer if an element being
+    -- dragged is part of a 'paired' form like as a map. If so then the element
+    -- will be dragged along with it's pair.
+    auto_drag_pairs = true,
+  },
+
   indent = {
     -- This controls how nvim-paredit handles indentation when performing operations which
     -- should change the indentation of the form (such as when slurping or barfing).
@@ -88,6 +95,9 @@ paredit.setup({
     [">e"] = { paredit.api.drag_element_forwards, "Drag element right" },
     ["<e"] = { paredit.api.drag_element_backwards, "Drag element left" },
 
+    [">p"] = { api.drag_pair_forwards, "Drag element pairs right" },
+    ["<p"] = { api.drag_pair_backwards, "Drag element pairs left" },
+
     [">f"] = { paredit.api.drag_form_forwards, "Drag form right" },
     ["<f"] = { paredit.api.drag_form_backwards, "Drag form left" },
 
@@ -287,6 +297,9 @@ require("nvim-paredit").setup({
       -- Accepts a Treesitter node and should return true or false depending on whether the given node
       -- can be considered a 'comment'
       node_is_comment = function(node) end,
+      -- Accepts a Treesitter node and should return a boolean indicating whether or not the given node contains
+      -- 'paired' elements. For example a clojure map (`{:a 1 :b 2}`)
+      node_contains_pairs = function(node) end,
       -- Accepts a Treesitter node representing a form and should return the 'edges' of the node. This
       -- includes the node text and the range covered by the node
       get_form_edges = function(node)
@@ -332,6 +345,8 @@ paredit.api.slurp_forwards()
 - **`barf_backwards`**
 - **`drag_element_forwards`**
 - **`drag_element_backwards`**
+- **`drag_pair_forwards`**
+- **`drag_pair_backwards`**
 - **`drag_form_forwards`**
 - **`drag_form_backwards`**
 - **`raise_element`**

lua/nvim-paredit/api/dragging.lua

@@ -1,5 +1,7 @@
 local traversal = require("nvim-paredit.utils.traversal")
+local common = require("nvim-paredit.utils.common")
 local ts = require("nvim-treesitter.ts_utils")
+local config = require("nvim-paredit.config")
 local langs = require("nvim-paredit.lang")
 
 local M = {}
@@ -44,24 +46,65 @@ function M.drag_form_backwards()
   ts.swap_nodes(root, sibling, buf, true)
 end
 
-function M.drag_element_forwards()
+local function find_current_pair(pairs, current_node)
+  for i, pair in ipairs(pairs) do
+    for _, node in ipairs(pair) do
+      if node:equal(current_node) then
+        return i, pair
+      end
+    end
+  end
+end
+
+local function drag_pairs(opts)
   local lang = langs.get_language_api()
   local current_node = lang.get_node_root(ts.get_node_at_cursor())
+  if not current_node then
+    return
+  end
 
-  local sibling = current_node:next_named_sibling()
-  if not sibling then
+  local direction = 1
+  if opts.reversed then
+    direction = -1
+  end
+
+  local parent = current_node:parent()
+  if not parent then
+    return
+  end
+
+  local children = traversal.get_children_ignoring_comments(parent, {
+    lang = lang,
+  })
+  local pairs = common.chunk_table(children, 2)
+  local chunk_index, pair = find_current_pair(pairs, current_node)
+
+  local corresponding_pair = pairs[chunk_index + direction]
+  if not corresponding_pair then
     return
   end
 
   local buf = vim.api.nvim_get_current_buf()
-  ts.swap_nodes(current_node, sibling, buf, true)
+  ts.swap_nodes(pair[2], corresponding_pair[2], buf, true)
+  ts.swap_nodes(pair[1], corresponding_pair[1], buf, true)
 end
 
-function M.drag_element_backwards()
+local function drag_element(opts)
   local lang = langs.get_language_api()
   local current_node = lang.get_node_root(ts.get_node_at_cursor())
 
-  local sibling = current_node:prev_named_sibling()
+  local parent = current_node:parent()
+  if opts.dragging.auto_drag_pairs and lang.node_contains_pairs and lang.node_contains_pairs(parent) then
+    return drag_pairs(opts)
+  end
+
+  local sibling
+  if opts.reversed then
+    sibling = current_node:prev_named_sibling()
+  else
+    sibling = current_node:next_named_sibling()
+  end
+
   if not sibling then
     return
   end
@@ -70,4 +113,44 @@ function M.drag_element_backwards()
   ts.swap_nodes(current_node, sibling, buf, true)
 end
 
+function M.drag_element_forwards(opts)
+  local drag_opts = vim.tbl_deep_extend(
+    "force",
+    {
+      dragging = config.config.dragging or {},
+    },
+    opts or {},
+    {
+      reversed = false,
+    }
+  )
+  drag_element(drag_opts)
+end
+
+function M.drag_element_backwards(opts)
+  local drag_opts = vim.tbl_deep_extend(
+    "force",
+    {
+      dragging = config.config.dragging or {},
+    },
+    opts or {},
+    {
+      reversed = true,
+    }
+  )
+  drag_element(drag_opts)
+end
+
+function M.drag_pair_forwards()
+  drag_pairs({
+    reversed = false,
+  })
+end
+
+function M.drag_pair_backwards()
+  drag_pairs({
+    reversed = true,
+  })
+end
+
 return M

lua/nvim-paredit/api/init.lua

@@ -15,6 +15,10 @@ local M = {
 
   drag_element_forwards = dragging.drag_element_forwards,
   drag_element_backwards = dragging.drag_element_backwards,
+
+  drag_pair_forwards = dragging.drag_pair_forwards,
+  drag_pair_backwards = dragging.drag_pair_backwards,
+
   drag_form_forwards = dragging.drag_form_forwards,
   drag_form_backwards = dragging.drag_form_backwards,
 

lua/nvim-paredit/defaults.lua

@@ -4,7 +4,7 @@ local unwrap = require("nvim-paredit.api.unwrap")
 local M = {}
 
 M.default_keys = {
-  ["<localleader>@"] = { unwrap.unwrap_form_under_cursor, "Splice sexp", },
+  ["<localleader>@"] = { unwrap.unwrap_form_under_cursor, "Splice sexp" },
 
   [">)"] = { api.slurp_forwards, "Slurp forwards" },
   [">("] = { api.barf_backwards, "Barf backwards" },
@@ -15,6 +15,9 @@ M.default_keys = {
   [">e"] = { api.drag_element_forwards, "Drag element right" },
   ["<e"] = { api.drag_element_backwards, "Drag element left" },
 
+  [">p"] = { api.drag_pair_forwards, "Drag element pairs right" },
+  ["<p"] = { api.drag_pair_backwards, "Drag element pairs left" },
+
   [">f"] = { api.drag_form_forwards, "Drag form right" },
   ["<f"] = { api.drag_form_backwards, "Drag form left" },
 
@@ -107,6 +110,12 @@ M.default_keys = {
 M.defaults = {
   use_default_keys = true,
   cursor_behaviour = "auto", -- remain, follow, auto
+  dragging = {
+    -- If set to `true` paredit will attempt to infer if an element being
+    -- dragged is part of a 'paired' form like as a map. If so then the element
+    -- will be dragged along with it's pair.
+    auto_drag_pairs = true,
+  },
   indent = {
     enabled = false,
     indentor = require("nvim-paredit.indentation.native").indentor,

lua/nvim-paredit/lang/clojure.lua

@@ -12,6 +12,17 @@ local form_types = {
   "anon_fn_lit",
 }
 
+local base_pair_types = {
+  map_lit = 0,
+  -- case = 2,
+  -- cond = 1,
+  -- condp = 3,
+}
+
+local fn_pair_names = {
+  vec_lit = { "let", "loop", "binding", "with-open", "with-redefs" },
+}
+
 M.whitespace_chars = { " ", "," }
 
 local function find_next_parent_form(current_node)
@@ -59,6 +70,31 @@ function M.node_is_comment(node)
   return node:type() == "comment"
 end
 
+function M.node_contains_pairs(node)
+  local node_type = node:type()
+  for type, offset in pairs(base_pair_types) do
+    if type == node_type then
+      return true, offset
+    end
+  end
+
+  local fn = traversal.get_prev_sibling_ignoring_comments(node, {
+    lang = M,
+  })
+  if not fn then
+    return false
+  end
+
+  local fn_name = vim.treesitter.get_node_text(fn, 0)
+
+  local fn_names = fn_pair_names[node:type()]
+  if fn_names and common.included_in_table(fn_names, fn_name) then
+    return true
+  end
+
+  return false
+end
+
 function M.get_form_edges(node)
   local outer_range = { node:range() }
 
@@ -67,19 +103,23 @@ function M.get_form_edges(node)
   local left_bracket_range = { form:field("open")[1]:range() }
   local right_bracket_range = { form:field("close")[1]:range() }
 
+  -- stylua: ignore
   local left_range = {
     outer_range[1], outer_range[2],
     left_bracket_range[3], left_bracket_range[4]
   }
+  -- stylua: ignore
   local right_range = {
     right_bracket_range[1], right_bracket_range[2],
     outer_range[3], outer_range[4],
   }
 
+  -- stylua: ignore
   local left_text = vim.api.nvim_buf_get_text(0,
     left_range[1], left_range[2],
     left_range[3], left_range[4],
     {})
+  -- stylua: ignore
   local right_text = vim.api.nvim_buf_get_text(0,
     right_range[1], right_range[2],
     right_range[3], right_range[4],

lua/nvim-paredit/lang/init.lua

@@ -1,5 +1,3 @@
-local common = require("nvim-paredit.utils.common")
-
 local langs = {
   clojure = require("nvim-paredit.lang.clojure"),
 }
@@ -14,13 +12,14 @@ local function keys(tbl)
   return result
 end
 
+--- @return table<string, function>
 function M.get_language_api()
   for l in string.gmatch(vim.bo.filetype, "[^.]+") do
     if langs[l] ~= nil then
       return langs[l]
     end
   end
-  return nil
+  error("Could not find language extension for filetype " .. vim.bo.filetype, vim.log.levels.ERROR)
 end
 
 function M.add_language_extension(filetype, api)

lua/nvim-paredit/utils/common.lua

@@ -9,6 +9,20 @@ function M.included_in_table(table, item)
   return false
 end
 
+function M.chunk_table(tbl, chunk_size)
+  local result = {}
+  for i = 1, #tbl, chunk_size do
+    local chunk = {}
+    for j = 0, chunk_size - 1 do
+      if tbl[i + j] then
+        table.insert(chunk, tbl[i + j])
+      end
+    end
+    table.insert(result, chunk)
+  end
+  return result
+end
+
 -- Compares the two given { col, row } position tuples and returns -1/0/1 depending
 -- on whether `a` is less than, equal to or greater than `b`
 --

lua/nvim-paredit/utils/traversal.lua

@@ -16,6 +16,22 @@ function M.find_nearest_form(current_node, opts)
   end
 end
 
+function M.get_children_ignoring_comments(node, opts)
+  local children = {}
+
+  local index = 0
+  local child = node:named_child(index)
+  while child do
+    if not child:extra() and not opts.lang.node_is_comment(child) then
+      table.insert(children, child)
+    end
+    index = index + 1
+    child = node:named_child(index)
+  end
+
+  return children
+end
+
 local function get_child_ignoring_comments(node, index, opts)
   if index < 0 or index >= node:named_child_count() then
     return