The harpoon list can have the wrong length

[abeldekat]

wrong_length.mp4

Hello @ThePrimeagen,

First off, thanks for merging this PR

Using my plugin harpoonline, I discovered that the length of the list can be wrong. I use:

require("harpoon"):list():length()

Up until recently this was working just fine.

See the video.

Reproduce:

1. Start from scratch
2. Harpoon 2 files
3. Open the UI
4. Delete both files
5. Reopen the UI: No items
6. Notice that harpoonline still shows 1: -> The latest call to length returned 1. See this code fragment
7. Use vim.print and notice that the length of the list is indeed 1 instead of 0

[ThePrimeagen]

Should be easy fix

[abeldekat]

I included a test for this scenario in the Harpoonline plugin.

[abeldekat]

When implementing toggle functionality in my config I found another side effect of this issue.

1. Open a file
2. require("harpoon"):list:add()
3. Open another file
4. require("harpoon"):list:add()
5. Go to the first file
6. require("harpoon"):list:remove_at(1)

Open the UI: There are two items. The first item is empty.

I would expect one item, and the second file on index 1.

I think this part might be the problem.

[abeldekat]

The toggle is working when using replace_at:

A.toggle = function()
  local list = H.get_current_list()
  local active_idx = H.find_active_idx(list)
  local len = #list.items
  if not active_idx or len == 0 then
    list:add()
  elseif active_idx == len then -- last item
    list:remove_at(active_idx) --
  else
    -- must replace with the last item in order to avoid gaps
    list:replace_at(active_idx, list.items[len])
  end
end

Unfortunately, I cannot submit a PR because I do not understand the purpose of methods determine_length and guess_length. As list.items is if of type HarpoonItem[], why not use table.insert and table.remove?