feat(clipboard): add OSC 52 clipboard support

This is opt-in as not all terminal emulators support OSC 52, so it is up
to the user to enable it explicitly.

runtime/doc/news.txt

@@ -208,6 +208,9 @@ The following new APIs and features were added.
 • The |TermResponse| autocommand event can be used with |v:termresponse| to
   read escape sequence responses from the terminal.
 
+• A clipboard provider which uses OSC 52 to copy the selection to the system
+  clipboard is now bundled by default. |clipboard-osc52|
+
 ==============================================================================
 CHANGED FEATURES                                                 *news-changed*
 

runtime/doc/provider.txt

@@ -253,7 +253,35 @@ For Windows WSL, try this g:clipboard definition:
                 \   },
                 \   'cache_enabled': 0,
                 \ }
+<
+							    *clipboard-osc52*
+Nvim bundles a clipboard provider that allows copying to the system clipboard
+using OSC 52. OSC 52 is an Operating System Command control sequence that
+writes the copied text to the terminal emulator. If the terminal emulator
+supports OSC 52 then it will write the copied text into the system clipboard.
 
+This is most useful when using Nvim remotely (e.g. via ssh) as Nvim does not
+have direct access to the system clipboard in that case.
+
+Because not all terminal emulators support OSC 52, this provider must be opted
+into explicitly by setting the following |g:clipboard| definition: >lua
+
+    vim.g.clipboard = {
+      name = 'OSC 52',
+      copy = {
+        ['+'] = require('vim.clipboard.osc52').copy,
+        ['*'] = require('vim.clipboard.osc52').copy,
+      },
+      paste = {
+        ['+'] = require('vim.clipboard.osc52').paste,
+        ['*'] = require('vim.clipboard.osc52').paste,
+      },
+    }
+<
+Note that not all terminal emulators support reading from the system clipboard
+(and even for those that do, users should be aware of the security
+implications), so using OSC 52 for pasting may not be possible.
+<
 ==============================================================================
 Paste							*provider-paste* *paste*
 

runtime/lua/vim/clipboard/osc52.lua

@@ -0,0 +1,38 @@
+local M = {}
+
+function M.copy(lines)
+  local s = table.concat(lines, '\n')
+  io.stdout:write(string.format('\x1b]52;;%s\x1b\\', vim.base64.encode(s)))
+end
+
+function M.paste()
+  local contents = nil
+  local id = vim.api.nvim_create_autocmd('TermResponse', {
+    callback = function(args)
+      local resp = args.data ---@type string
+      local encoded = resp:match('\x1b%]52;%w?;([A-Za-z0-9+/=]*)')
+      if encoded then
+        contents = vim.base64.decode(encoded)
+        return true
+      end
+    end,
+  })
+
+  io.stdout:write('\x1b]52;;?\x1b\\')
+
+  vim.wait(1000, function()
+    return contents ~= nil
+  end)
+
+  -- Delete the autocommand if it didn't already delete itself
+  pcall(vim.api.nvim_del_autocmd, id)
+
+  if contents then
+    return vim.split(contents, '\n')
+  end
+
+  vim.notify('Timed out waiting for a clipboard response from the terminal', vim.log.levels.WARN)
+  return 0
+end
+
+return M