feat(clipboard): enable OSC 52 clipboard provider by default (#26064)

Use the XTGETTCAP sequence to determine if the host terminal supports
the OSC 52 sequence and, if it does, enable the OSC 52 clipboard
provider by default.

This is only done automatically when all of the following are true:

  1. Nvim is running in the TUI
  2. 'clipboard' is not set to unnamed or unnamedplus
  3. g:clipboard is unset
  4. Nvim is running in an SSH connection ($SSH_TTY is set)
  5. Nvim is not running inside tmux ($TMUX is unset)

2 files changed, 121 insertions, 46 deletions

diff --git a/runtime/lua/vim/termcap.lua b/runtime/lua/vim/termcap.lua
new file mode 100644
index 0000000000..0eefc5eee4
--- /dev/null
+++ b/runtime/lua/vim/termcap.lua
@@ -0,0 +1,60 @@
+local M = {}
+
+--- Query the host terminal emulator for terminfo capabilities.
+---
+--- This function sends the XTGETTCAP DCS sequence to the host terminal emulator asking the terminal
+--- to send us its terminal capabilities. These are strings that are normally taken from a terminfo
+--- file, however an up to date terminfo database is not always available (particularly on remote
+--- machines), and many terminals continue to misidentify themselves or do not provide their own
+--- terminfo file, making the terminfo database unreliable.
+---
+--- Querying the terminal guarantees that we get a truthful answer, but only if the host terminal
+--- emulator supports the XTGETTCAP sequence.
+---
+--- @param caps string|table A terminal capability or list of capabilities to query
+--- @param cb function(cap:string, seq:string) Function to call when a response is received
+function M.query(caps, cb)
+  vim.validate({
+    caps = { caps, { 'string', 'table' } },
+    cb = { cb, 'f' },
+  })
+
+  if type(caps) ~= 'table' then
+    caps = { caps }
+  end
+
+  local count = #caps
+
+  vim.api.nvim_create_autocmd('TermResponse', {
+    callback = function(args)
+      local resp = args.data ---@type string
+      local k, v = resp:match('^\027P1%+r(%x+)=(%x+)$')
+      if k and v then
+        local cap = vim.text.hexdecode(k)
+        local seq =
+          vim.text.hexdecode(v):gsub('\\E', '\027'):gsub('%%p%d', ''):gsub('\\(%d+)', string.char)
+
+        -- TODO: When libtermkey is patched to accept BEL as an OSC terminator, this workaround can
+        -- be removed
+        seq = seq:gsub('\007$', '\027\\')
+
+        cb(cap, seq)
+
+        count = count - 1
+        if count == 0 then
+          return true
+        end
+      end
+    end,
+  })
+
+  local encoded = {} ---@type string[]
+  for i = 1, #caps do
+    encoded[i] = vim.text.hexencode(caps[i])
+  end
+
+  local query = string.format('\027P+q%s\027\\', table.concat(encoded, ';'))
+  io.stdout:write(query)
+end
+
+return M
diff --git a/runtime/lua/vim/ui/clipboard/osc52.lua b/runtime/lua/vim/ui/clipboard/osc52.lua
index 035a6abb86..f1d454010f 100644
--- a/runtime/lua/vim/ui/clipboard/osc52.lua
+++ b/runtime/lua/vim/ui/clipboard/osc52.lua
@@ -1,60 +1,75 @@
 local M = {}
 
-function M.copy(lines)
-  local s = table.concat(lines, '\n')
-  io.stdout:write(string.format('\027]52;;%s\027\\', vim.base64.encode(s)))
+--- Return the OSC 52 escape sequence
+---
+--- @param clipboard string The clipboard to read from or write to
+--- @param contents string The Base64 encoded contents to write to the clipboard, or '?' to read
+---                        from the clipboard
+local function osc52(clipboard, contents)
+  return string.format('\027]52;%s;%s\027\\', clipboard, contents)
 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('\027%]52;%w?;([A-Za-z0-9+/=]*)')
-      if encoded then
-        contents = vim.base64.decode(encoded)
-        return true
-      end
-    end,
-  })
-
-  io.stdout:write('\027]52;;?\027\\')
-
-  local ok, res
-
-  -- Wait 1s first for terminals that respond quickly
-  ok, res = vim.wait(1000, function()
-    return contents ~= nil
-  end)
-
-  if res == -1 then
-    -- If no response was received after 1s, print a message and keep waiting
-    vim.api.nvim_echo(
-      { { 'Waiting for OSC 52 response from the terminal. Press Ctrl-C to interrupt...' } },
-      false,
-      {}
-    )
-    ok, res = vim.wait(9000, function()
+function M.copy(reg)
+  local clipboard = reg == '+' and 'c' or 's'
+  return function(lines)
+    local s = table.concat(lines, '\n')
+    io.stdout:write(osc52(clipboard, vim.base64.encode(s)))
+  end
+end
+
+function M.paste(reg)
+  local clipboard = reg == '+' and 'c' or 's'
+  return function()
+    local contents = nil
+    local id = vim.api.nvim_create_autocmd('TermResponse', {
+      callback = function(args)
+        local resp = args.data ---@type string
+        local encoded = resp:match('\027%]52;%w?;([A-Za-z0-9+/=]*)')
+        if encoded then
+          contents = vim.base64.decode(encoded)
+          return true
+        end
+      end,
+    })
+
+    io.stdout:write(osc52(clipboard, '?'))
+
+    local ok, res
+
+    -- Wait 1s first for terminals that respond quickly
+    ok, res = vim.wait(1000, function()
       return contents ~= nil
     end)
-  end
 
-  if not ok then
-    vim.api.nvim_del_autocmd(id)
     if res == -1 then
-      vim.notify(
-        'Timed out waiting for a clipboard response from the terminal',
-        vim.log.levels.WARN
+      -- If no response was received after 1s, print a message and keep waiting
+      vim.api.nvim_echo(
+        { { 'Waiting for OSC 52 response from the terminal. Press Ctrl-C to interrupt...' } },
+        false,
+        {}
       )
-    elseif res == -2 then
-      -- Clear message area
-      vim.api.nvim_echo({ { '' } }, false, {})
+      ok, res = vim.wait(9000, function()
+        return contents ~= nil
+      end)
+    end
+
+    if not ok then
+      vim.api.nvim_del_autocmd(id)
+      if res == -1 then
+        vim.notify(
+          'Timed out waiting for a clipboard response from the terminal',
+          vim.log.levels.WARN
+        )
+      elseif res == -2 then
+        -- Clear message area
+        vim.api.nvim_echo({ { '' } }, false, {})
+      end
+      return 0
     end
-    return 0
-  end
 
-  -- If we get here, contents should be non-nil
-  return vim.split(assert(contents), '\n')
+    -- If we get here, contents should be non-nil
+    return vim.split(assert(contents), '\n')
+  end
 end
 
 return M