screenstring() doesn't recognize floating windows in child Neovim process

[echasnovski]

Describe the bug

The screenstring() executed inside child Neovim process through RPC doesn't recognize floating windows.

This seems to have the same root cause as #21886. When applying the workaround from that issue (spawn another process to attach a UI), it works locally, but probably has the same problems as in that issue.

This might also be related to #19020, which actually made screenstring() recognize floating windows.

Steps to reproduce

• Create 'init-child-screenstring_floating.lua' with the following content:

  init-child-screenstring_floating.lua

  _G.new_child = function(nvim_executable)
    -- Create new child process
    local stdin = vim.loop.new_pipe(true)
    local stdout = vim.loop.new_pipe(true)
    local stderr = vim.loop.new_pipe(true)
  
    local address = vim.fn.tempname()
  
    vim.loop.spawn(nvim_executable or 'nvim', {
      stdio = { stdin, stdout, stderr },
      args = { '--clean', '--listen', address },
    }, function() end)
  
    -- Wait for Neovim to open
    vim.loop.sleep(200)
  
    -- Connect
    local channel = vim.fn.sockconnect('pipe', address, { rpc = true })
  
    -- Follow advice from https://github.com/neovim/neovim/issues/21630
    stdin:close()
    stdout:close()
    stderr:close()
  
    -- Create helper methods for easier demonstration
    local child = { channel = channel }
  
    -- Call `screenstring()` inside child process
    child.screenstring = function(row, col)
      return vim.rpcrequest(channel, 'nvim_exec_lua', 'return vim.fn.screenstring(...)', { row, col })
    end
  
    -- Main setup: some normal text and floating window partially covering it
    child.setup_text_with_float = function()
      vim.rpcrequest(channel, 'nvim_buf_set_lines', 0, 0, -1, true, { 'aaaa' })
  
      local buf_id = vim.rpcrequest(channel, 'nvim_create_buf', true, true)
      vim.rpcrequest(channel, 'nvim_buf_set_lines', buf_id, 0, -1, true, { 'bb ' })
  
      vim.rpcrequest(
        channel,
        'nvim_open_win',
        buf_id,
        false,
        { relative = 'editor', width = 3, height = 1, row = 0, col = 0 }
      )
    end
  
    return child
  end

  It is basically a creation-connection to full child process (following advice from Can't receive an answer from RPC request to Neovim created as child process #21630) and then a couple helper wrappers to get and set information in child process through RPC requests.

• Assuming nvim_nightly_g825 is the executable for latest nightly, run nvim_nightly_g825 -u init-child-screenstring_floating.lua.

• :lua child = new_child('nvim_nightly_g825'). This should create and connect to child process running latest nightly.

• :lua child.setup_text_with_float(). This should add normal text aaaa covered by bb text in floating window. In total, bb a should be a visible text.

• Execute :lua print(child.screenstring(1, 1)). It prints a, but should print b.

Expected behavior

Always prints actually visible screen string.

There are three notes here:

• It works in Neovim 0.8.2 (with new_child('nvim'), assuming nvim is Neovim 0.8.2).

• It works if applied the workaround from screenstring() doesn't work for Command line in child Neovim process #21886. So adding these lines before local channel = ... makes it work locally:

  vim.loop.spawn(nvim_executable or 'nvim', {
    args = { '--remote-ui', '--server', address },
  }, function() end)

• It works if executed not in child process, but in "normal" one:

  • Create 'init-screenstring_floating.lua' with the following content:

  vim.api.nvim_buf_set_lines(0, 0, -1, true, { 'aaaa' })
  
  local buf_id = vim.api.nvim_create_buf(true, true)
  vim.api.nvim_buf_set_lines(buf_id, 0, -1, true, { 'bb ' })
  
  vim.api.nvim_open_win(buf_id, false, { relative = 'editor', width = 3, height = 1, row = 0, col = 0 })

  • Run nvim_nightly_g825 -u init-screenstring_floating.lua.
  • :echo screenstring(1, 1). It indeed prints b.

Neovim version (nvim -v)

NVIM v0.9.0-dev-825+g843c9025a

Vim (not Nvim) behaves the same?

No (doesn't have this functionality)

Operating system/version

EndeavourOS Linux x86_64 (6.1.7-arch1-1)

Terminal name/version

st-0.9

$TERM environment variable

st-256color

Installation

appimage

[echasnovski]

As suggested in #21886, using vim.fn.jobstart(..., { pty = true }) instead of vim.loop.spawn() fixes the issue. With the following 'init-child-screenstring_floating.lua' screenstring() returns expected result from floating windows:

init-child-screenstring_floating.lua

_G.new_child = function(nvim_executable)
  local address = vim.fn.tempname()

  vim.fn.jobstart({ nvim_executable or 'nvim', '--clean', '--listen', address }, { pty = true })

  -- Wait for Neovim to open
  vim.loop.sleep(200)

  -- Connect
  local channel = vim.fn.sockconnect('pipe', address, { rpc = true })

  -- Create helper methods for easier demonstration
  local child = { channel = channel }

  -- Call `screenstring()` inside child process
  child.screenstring = function(row, col)
    return vim.rpcrequest(channel, 'nvim_exec_lua', 'return vim.fn.screenstring(...)', { row, col })
  end

  -- Main setup: some normal text and floating window partially covering it
  child.setup_text_with_float = function()
    vim.rpcrequest(channel, 'nvim_buf_set_lines', 0, 0, -1, true, { 'aaaa' })

    local buf_id = vim.rpcrequest(channel, 'nvim_create_buf', true, true)
    vim.rpcrequest(channel, 'nvim_buf_set_lines', buf_id, 0, -1, true, { 'bb ' })

    vim.rpcrequest(
      channel,
      'nvim_open_win',
      buf_id,
      false,
      { relative = 'editor', width = 3, height = 1, row = 0, col = 0 }
    )
  end

  return child
end

I don't have problem with this being close, but it still seems to not be a good behavior to have in an otherwise valid child process.