Nvim-dap, Pytest, Debugpy and Docker

Firstly, this isn’t an issue with the plugin at all, more of a general question on being able to use vim-ultest to debug remotely into a Docker container.

With my current config (for reference rather than to understand), I use a pretty hefty command to pass to the command line which triggers Docker to wait for any feedback from nvim-dap:

docker-compose -f "./docker-compose.yml" exec -T -w /usr/src/app debug python -m debugpy --listen ' ..
                debug_host .. ':' .. debug_port .. ' --wait-for-client -m pytest ' .. test_method[1]

Where test_method is the test name for the nearest test (something I pinched from vim-test). Using the instructions in the vim-ultest docs, combined with my previous setup, I form the following:

require("ultest").setup({
        builders = {
            ['python#pytest'] = function(cmd)
                local debug_host = '0.0.0.0'
                local debug_port = 5678

                local test_method = fn['test#python#pytest#build_position']('nearest', {
                    file = fn['expand']('%'),
                    line = fn['line']('.'),
                    col = fn['col']('.')
                })

                local args = 'docker-compose -f "./docker-compose.yml" exec -T -w /usr/src/app debug python -m debugpy --listen ' .. debug_host .. ':' .. debug_port .. ' --wait-for-client -m pytest ' .. test_method[1]
                return {
                    dap = {
                        type = "python",
                        request = "attach",
                        connect = {
                            host = debug_host,
                            port = debug_port
                        },
                        args = args,
                        mode = "remote",
                        name = "Remote Attached Debugger",
                        cwd = fn.getcwd(),
                        pathMappings = {{
                            localRoot = fn.getcwd(), -- Wherever your Python code lives locally.
                            remoteRoot = "/usr/src/app" -- Wherever your Python code lives in the container.
                        }}
                    }
                }
            end
        }
    })

When I run this with UltestDebugNearest I get Invalid adapter: nil which is an nvim-dap error. Which seems odd as I use it with nvim-dap in my previous setup.

Is there anything obvious I may be overlooking? Granted I need to actually make use of the vim-ultest cmd function to pass to nvim-dap.

[rcarriga]

That’s great to hear! 😁 As an alternative to the wait, could you add the -d flag to the exec command to detach? If that works OK (provided debugpy doesn’t require an interactive session for some reason) then it should be as simple as swapping

            g.debug_job_id = fn.jobstart(docker_cmd)

with

            g.debug_job_id = fn.system(docker_cmd)

which will block until it returns.

I’d definitely like to add this to the wiki btw!

[rcarriga]

So I’m not too familiar with the docker side of nvim-dap but to me it looks like config you’re returning to vim-ultest is the wrong one.

From what I can tell you should be running your docker command as a separate job (using vim.loop.spawn, jobstart or whatever) and then return the pythonAttachConfig from the example in the docs. So it’d be something like

require("ultest").setup(
  {
    builders = {
      ["python#pytest"] = function(cmd)
        local docker_cmd =
          'docker-compose -f "./docker-compose.yml" exec -T -w /usr/src/app debug python -m debugpy --listen 0.0.0.0:5678 --wait-for-client -m ' ..
          table.concat(cmd, " ")

        -- You can attach output handlers but anything needed by vim-ultest should be caught by the "attach" adapter
        vim.fn.jobstart(docker_cmd)

        return {
          dap = {
            type = "python",
            request = "attach",
            connect = {
              port = 5678, -- Need to open bind this port to your container
              host = "0.0.0.0"
            },
            mode = "remote",
            name = "Remote Attached Debugger",
            cwd = vim.fn.getcwd(),
            pathMappings = {
              {
                localRoot = vim.fn.getcwd(),
                remoteRoot = "/usr/src/app" -- Likely need to change this
              }
            }
          }
        }
      end
    }
  }
)