Debug Adapter does not support stepping backwards with undodb

[SteveWolligandt]

Hi!

With cpptools (OpenDebugAD7) and specifying miDebuggerPath=udb in the configuration nvim-dap says

Debug Adapter does not support stepping backwards

I know that cpptools can do this since there is a plugin for VSCode for udb that uses cpptools.
(https://marketplace.visualstudio.com/items?itemName=Undo.udb)

I am using this config:

function M.setup()
  local dap = require('dap')
  dap.adapters.cppdbg = {
    name = 'cppdbg',
    type = 'executable',
    command = vim.fn.stdpath('data') .. '/mason/bin/OpenDebugAD7',
  }
  dap.configurations.cpp = {
    {
      name = 'Debug Program',
      type = 'cppdbg',
      request = 'launch',
      MIMode = 'gdb',
      cwd = '${workspaceFolder}',
      udb='live',
      miDebuggerPath = 'udb',
      stopAtEntry = true,
      program = function()
        return M.inputAndWait('Select program')
      end,
    },
  }
end

Is that a bug of nvim-dap or is there really a flag that states that cpptools is not able to do reverse debugging?

Regards,
Steve

[SteveWolligandt]

When doing in the dap repl

-exec rn

for reverse next

I am getting this for like a thousand times:

Program received signal SIGSTOP, Stopped (signal).
The program has exited, but is still being debugged.
You can use UDB reverse commands to go backwards; see "help udb" for details.
0x00007ffff71b2da9 in _exit () from /lib64/libc.so.6

[SteveWolligandt]

That seems to be solvable in VSCode:
microsoft/vscode-cpptools#2130 (comment)

Unfortunately it does not work for nvim-dap

[mfussenegger]

The debug adapter would have to set the supportsStepBack capability. Based on the linked issue cpptools currently doesn't set it.

But the linked workaround sounds like it could work. What's the problem?

[SteveWolligandt]

Oh I just understood what that acutally does. Executing

require'dap'.continue()

then actually steps back. At least this is working.
Do you maybe know how I get cpptools to set the supportsStepBack capability? It feels as if that beast is not really well documented.

[SteveWolligandt]

It seems the cpptools guys are planning to do that:
microsoft/MIEngine#1037 (comment)
However than I have another question. I saw that there is the possiblity to create custom commands in the repl. Unfortunately I could not figure out how to define a custom commands. Is there a way to do this?

Or is there a way to execute repl commands from lua? That would even be better!

(BTW thanks for all the effort to develop nvim-dap. It is so useful!)

[SteveWolligandt]

By adding theses three lines in lua/dap/repl.lua

function M.exec(text)
  execute(text)
end

one can execute repl commands from lua by doing

local cmd = '...'
require('dap').repl.exec(cmd)

This would be a nice feature I think. I guess there are missing some sanity checks if a session is currently active.

[QuantumKuba]

Sorry for the bump, but was this added yet by any chance?