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" },
 
@@ -246,15 +256,70 @@ vim.lsp.buf.format({
 end
 
 require("nvim-paredit").setup({
-indent = {
-  enabled = true,
-  indentor = lsp_indent,
-},
+  indent = {
+    enabled = true,
+    indentor = lsp_indent,
+  },
 })
 ```
 
 </details>
 
+## Pairwise Dragging
+
+Nvim-paredit has support for dragging elements pairwise. If an element being dragged is within a form that contains
+pairs of elements (such as a clojure `map`) then the element will be dragged along with it's pair.
+
+For example:
+
+```clojure
+{:a 1
+ |:b 2}
+;; Drag backwards
+{|:b 2
+ :a 1}
+```
+
+This is enabled by default and can be disabled by setting `dragging.auto_drag_pairs = false`.
+
+Pairwise dragging works using treesitter queries to identify element pairs within some localized node. This means you
+can very easily extend the paredit pairwise implementation by simply adding new treesitter queries to your nvim
+configuration.
+
+You might want to extend if:
+
+1) You are a language extension author and want to add pairwise dragging support to your extension.
+2) You want to add support for some syntax not supported by nvim-paredit.
+
+This is especially useful if you have your own clojure macros that you want to enable pairwise dragging on.
+
+All you need to do to extend is to add a new file called `queries/<language>/paredit/pairwise.scm` in your nvim config
+directory. Make sure to include the `;; extends` directive to the file or you will overwrite any pre-existing queries
+defined by nvim-paredit or other language extensions.
+
+As an example if you want to add support for the following clojure macro:
+
+```clojure
+(defmacro my-custom-bindings [bindings & body]
+  ...)
+
+(my-custom-bindings [a 1
+                     b 2]
+  (println a b))
+```
+
+You can add the following TS query
+
+```scm
+;; extends
+
+(list_lit
+  (sym_lit) @fn-name
+  (vec_lit
+    (_) @pair)
+  (#eq? @fn-name "my-custom-bindings"))
+```
+
 ## Language Support
 
 As this is built using Treesitter it requires that you have the relevant Treesitter grammar installed for your language
@@ -332,6 +397,8 @@ 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 +1,8 @@
 local traversal = require("nvim-paredit.utils.traversal")
+local common = require("nvim-paredit.utils.common")
+local ts_utils = require("nvim-paredit.utils.ts")
 local ts = require("nvim-treesitter.ts_utils")
+local config = require("nvim-paredit.config")
 local langs = require("nvim-paredit.lang")
 
 local M = {}
@@ -44,24 +47,79 @@ function M.drag_form_backwards()
   ts.swap_nodes(root, sibling, buf, true)
 end
 
-function M.drag_element_forwards()
-  local lang = langs.get_language_api()
-  local current_node = lang.get_node_root(ts.get_node_at_cursor())
+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 sibling = current_node:next_named_sibling()
-  if not sibling then
+local function drag_node_in_pair(current_node, nodes, opts)
+  local direction = 1
+  if opts.reversed then
+    direction = -1
+  end
+
+  local pairs = common.chunk_table(nodes, 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)
+  if pair[2] and corresponding_pair[2] then
+    ts.swap_nodes(pair[2], corresponding_pair[2], buf, true)
+  end
+  if pair[1] and corresponding_pair[1] then
+    ts.swap_nodes(pair[1], corresponding_pair[1], buf, true)
+  end
 end
 
-function M.drag_element_backwards()
+local function drag_pair(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 pairwise_nodes = ts_utils.find_pairwise_nodes(current_node, opts)
+  if not pairwise_nodes then
+    local parent = current_node:parent()
+    if not parent then
+      return
+    end
+
+    pairwise_nodes = traversal.get_children_ignoring_comments(parent, {
+      lang = lang,
+    })
+  end
+
+  drag_node_in_pair(current_node, pairwise_nodes, opts)
+end
+
+local function drag_element(opts)
+  local lang = langs.get_language_api()
+  local current_node = lang.get_node_root(ts.get_node_at_cursor())
+
+  if opts.dragging.auto_drag_pairs then
+    local pairwise_nodes = ts_utils.find_pairwise_nodes(current_node, { lang = lang })
+    if pairwise_nodes then
+      return drag_node_in_pair(current_node, pairwise_nodes, opts)
+    end
+  end
+
+  local sibling
+  if opts.reversed then
+    sibling = current_node:prev_named_sibling()
+  else
+    sibling = current_node:next_named_sibling()
+  end
 
-  local sibling = current_node:prev_named_sibling()
   if not sibling then
     return
   end
@@ -70,4 +128,44 @@ 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_pair({
+    reversed = false,
+  })
+end
+
+function M.drag_pair_backwards()
+  drag_pair({
+    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/api/selections.lua

@@ -41,7 +41,7 @@ function M.get_range_around_form()
 end
 
 function M.get_range_around_top_level_form()
-  return get_range_around_form_impl(traversal.get_top_level_node_below_document)
+  return get_range_around_form_impl(traversal.find_local_root)
 end
 
 local function select_around_form_impl(range)
@@ -93,7 +93,7 @@ function M.get_range_in_form()
 end
 
 function M.get_range_in_top_level_form()
-  return get_range_in_form_impl(traversal.get_top_level_node_below_document)
+  return get_range_in_form_impl(traversal.find_local_root)
 end
 
 local function select_in_form_impl(range)

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

@@ -67,19 +67,23 @@ 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`
 --