Cannot launch osv at the beginning of a neovim configuration

[ramboman]

I would like to debug some code, in my neovim configuration, that executes at the start of nvim.

Setup

I made and reduced this setup solely for the purpose of reproducing the problem

OS: Debian 12
NVIM version: v0.10.0
NVIM package manager: lazy.nvim

~/.config/nvim/init.lua:

local lazydir = vim.fn.stdpath("data") .. "/lazy"

-- Debug
local osvpath = lazydir .. "/one-small-step-for-vimkind"
if (vim.uv or vim.loop).fs_stat(osvpath) then
  local nvim_debug = vim.fn.getenv("NVIM_DEBUG")
  if nvim_debug ~= vim.NIL and nvim_debug == "y" then
    vim.opt.rtp:prepend(osvpath)
    require("osv").launch({ port = 8086 })
    vim.print("Press any key to continue")
    vim.fn.getchar()
  end
end

-- Code to debug
local some_number = require("do_something").add_some(1)

-- lazy.nvim bootstrap
local lazypath = lazydir .. "/lazy.nvim"
if not (vim.uv or vim.loop).fs_stat(lazypath) then
  vim.fn.system({
    "git",
    "clone",
    "--filter=blob:none",
    "https://github.com/folke/lazy.nvim.git",
    "--branch=stable", -- latest stable release
    lazypath,
  })
end
vim.opt.rtp:prepend(lazypath)

vim.g.mapleader = " " -- Make sure to set `mapleader` before lazy so your mappings are correct
vim.g.maplocalleader = "\\" -- Same for `maplocalleader`

-- Keybindings
vim.api.nvim_set_keymap('n', '<F4>', [[:lua require"dapui".toggle({})<CR>]], { noremap = true })
vim.api.nvim_set_keymap('n', '<F8>', [[:lua require"dap".toggle_breakpoint()<CR>]], { noremap = true })
vim.api.nvim_set_keymap('n', '<F9>', [[:lua require"dap".continue()<CR>]], { noremap = true })
vim.api.nvim_set_keymap('n', '<F10>', [[:lua require"dap".step_over()<CR>]], { noremap = true })
vim.api.nvim_set_keymap('n', '<S-F10>', [[:lua require"dap".step_into()<CR>]], { noremap = true })
vim.api.nvim_set_keymap('n', '<F12>', [[:lua require"dap.ui.widgets".hover()<CR>]], { noremap = true })
vim.api.nvim_set_keymap('n', '<F5>', [[:lua require"osv".launch({port = 8086})<CR>]], { noremap = true })

-- Install packages
require("lazy").setup({
  { "mfussenegger/nvim-dap", },
  {
    "rcarriga/nvim-dap-ui",
    dependencies = {
      "mfussenegger/nvim-dap",
      "nvim-neotest/nvim-nio",
    },
    keys = {
    },
    config = function()
      local dap = require("dap")
      local dapui = require("dapui")
      dapui.setup()
      dap.listeners.after.event_initialized["dapui_config"] = function()
        dapui.open()
      end
      dap.listeners.before.event_terminated["dapui_config"] = function()
        dapui.close()
      end
      dap.listeners.before.event_exited["dapui_config"] = function()
        dapui.close()
      end
    end
  },
  {
    "jbyuki/one-small-step-for-vimkind",
    dependencies = { "mfussenegger/nvim-dap", },
    config = function()
      local dap = require("dap")
      dap.configurations.lua = {
        {
          type = "nlua",
          request = "attach",
          name = "Attach to running Neovim instance",
        },
      }
      dap.adapters.nlua = function(callback, conf)
        callback({
          type = "server",
          host = conf.host or "127.0.0.1",
          port = conf.port or 8086,
        })
      end
    end,
  },
})

~/.config/nvim/lua/do_something.lua:

local M = {
  add_some = function(a)
    local b = a + 1
    local c = b + 1
    local d = c + 1
    return d
  end,
}

return M

The general idea

I added a debug code (-- Debug) at the beginning of ~/.config/nvim/init.lua. I would like this code to launch osv if nvim was started with the environment variable NVIM_DEBUG equal "y". Right after osv is launched, nvim has to wait for a key press, so I have the time to setup the debugger on the other nvim. After I press any key on the debugged nvim, it has to continue its execution until it reaches a breakpoint.

How to reproduce the problem

• Start nvim so it setups everything
• Close nvim
• Open the file containing the code to debug:

$ nvim "~/.config/nvim/lua/do_something.lua"

• Place a break point in the add_some function
• Start a nvim instance to debug:

$ NVIM_DEBUG=y nvim

Expected course of action

• The debugged nvim instance launchs osv
• It waits for a key press
• I press <F4> in the client nvim to open the debug ui
• I press <F9> so the dap connects to the debugged nvim
• I press any key in the debugged nvim
• The debugged nvim stops at the break points so I can start debugging

Actual course of action:

• The debugged nvim prints this error message:

Server failed to launch on port 8086

Questions

• How can I launch osv properly at the beginning of a configuration so I can debug it?

[ramboman]

I made some modifications to my debug code:

• The nvim debug environment variable is now NVIM_CONFIG_DEBUG
• I temporarily change NVIM_CONFIG_DEBUG to something that is not "y" before launching osv and reset it back to its original value right after.

Here is the code:

local lazydir = vim.fn.stdpath("data") .. "/lazy"

-- Debug
local osvpath = lazydir .. "/one-small-step-for-vimkind"
if (vim.uv or vim.loop).fs_stat(osvpath) then
  local nvim_config_debug = vim.env.NVIM_CONFIG_DEBUG
  if nvim_config_debug ~= vim.NIL and nvim_config_debug == "y" then
    vim.opt.rtp:prepend(osvpath)
    vim.env.NVIM_CONFIG_DEBUG = ""
    require("osv").launch({ port = 8086 })
    vim.env.NVIM_CONFIG_DEBUG = nvim_config_debug
    vim.print("Press any key to continue")
    vim.fn.getchar()
  end
end

Now I can start the debugger at the beginning of the config.

I will leave this issue open since, osv, itself, alone, cannot be started at the beginning of the configuration. This is a hack to avoid this problem.

Thank you @jbyuki!

[jbyuki]

Nice one!

Yes, this is an on-going issue that needs better thought. Leaving it open will remind me/others that it's a problem that needs solving. Glad that it worked in your case for now.

[blakedietz]

I just ran into this very same issue the other day. Thanks for the recommendation @ramboman.

[jbyuki]

A more elegant way to debug configuration files has been added. The help file goes into more details on how it is done.

doc/osv.txt

I will close this for now as a more permanent solution has been now added to the plugin.

[jbyuki]

Here it is in action.

output.mp4