How to create conditional breakpoints

[CharlesARoy]

From issues such as this it seems like nvim-dap supports creating conditional breakpoints, but I can't find any documentation on how.

When I look at the available commands for DAP, I see DapToggleBreakpoint but nothing for conditional breakpoints.

Any help is appreciated!

[mfussenegger]

See :help dap.toggle_breakpoint

[CharlesARoy]

Thanks @mfussenegger! I don't mean to be obtuse but I'm still a little confused about two things:

1. I thought that a conditional breakpoint was a breakpoint that triggered when some condition was met irrespective of line/location in the script. E.g. the script stops if the variable i equals 5 anywhere in the script. Does such functionality exist?
2. I tried to use a conditional breakpoint in a simple Python script but it didn't seem to work as expected.

I ran this command in Nvim: :lua require('dap').toggle_breakpoint(i==5) which created a breakpoint as seen here:

Then when I run the script, it stopped at the breakpoint even though the variable i was not equal to 5. Is that normal?

[mfussenegger]

1. Conditional breakpoints are still depending on the line where you place them. Variables can be in different scopes and it needs to know which ones you're referring to.

2. works fine for me. Make sure the condition is a string. :lua require('dap').toggle_breakpoint('i==5') otherwise i == 5 gets treated as lua and is evaluated to false (assuming i doesn't exist as global variable in the lua interpreter)

[leosmaia21]

Hello, in codelldb how can i set a break with a function, like break if i == strlen(s)?

[fidelski]

Thanks a lot for this functionality! It's great to have that in neovim! I am still struggling to make conditional breakpoints work. I can specify the condition, it is shown in the dap-ui Breakpoints window and repl does not report any error. Still the debugger stops at the breakpoint even though the condition is not met.

So e.g. I set the condition to 'i == 38' in a for-loop over an incrementing i but the debugger stops there for every value of i.

Another example, I set the condition to 'result == false' on this code:

result = validate_checksum(fops, fp, header.checksum, header.size);
if (result) { // <- Breakpoint set here
     fops.seek(fp, next_pos, SEEK_SET);
}

But the debugger stops every time the breakpoint is reached, no matter what result is.

I tried to set the condition as string with 'result == false' and without quotes as result == false but no difference, it doesn't work either way.

What am I missing?

[sleeptightAnsiC]

Take a look at code from PR #1325; it enhances DapToggleBreakpoint command with optional condition.

[fidelski]

Thanks for the hint! I indeed didn't catch up with the latest changes. I can confirm that my problem does not exist anymore. I can now successfully create conditional breakpoints that correctly get hit only when the condition is true.

[johan-lejdung]

Here are the keymaps I use specifically for breakpoints, it could perhaps help someone:

Lazyvim

return {
  "mfussenegger/nvim-dap",
  dependencies = {
    ...
  },
  keys = {
    ....,
    {
      "<leader>db",
      function()
        require("dap").toggle_breakpoint()
      end,
      desc = "Debug: Toggle Breakpoint",
    },
    {
      "<leader>dB",
      function()
        local condition = vim.fn.input("Breakpoint condition (optional): ")
        local hit_condition = vim.fn.input("Hit count (optional): ")

        -- Convert empty strings to nil
        condition = condition ~= "" and condition or nil
        hit_condition = hit_condition ~= "" and hit_condition or nil

        require("dap").toggle_breakpoint(condition, hit_condition)
      end,
      desc = "Debug: Toggle Advanced Breakpoint",
    },
  },
  ...
}