Inspect nvim highlight groups under mouse cursor in a floating window

inspector.lua

local M = {}

-- Cache for module state
local state = {
  buf = nil,
  win = nil,
  ns = nil,
  width = 34,
  uses_mousemoveevent = vim.o.mousemoveevent,
}

-- Initialize the module
local function init()
  if not state.buf then
    state.buf = vim.api.nvim_create_buf(false, true)
    vim.bo[state.buf].filetype = "inspector"
    vim.bo[state.buf].bufhidden = "hide"
  end
  if not state.ns then
    state.ns = vim.api.nvim_create_namespace("inspect_word")
  end
end

-- Format the inspection info into displayable lines
local function format_inspect_info(inspect_info)
  local lines = {}
  local highlights = {}

  -- Helper to add a line with optional highlighting
  local function add_line(text, hl_group)
    table.insert(lines, text)
    if hl_group then
      table.insert(highlights, { line = #lines - 1, hl_group = hl_group })
    end
  end

  -- Treesitter highlights
  if inspect_info.treesitter and #inspect_info.treesitter > 0 then
    add_line("Treesitter", "@function.call.lua")
    for _, entry in ipairs(inspect_info.treesitter) do
      local text = string.format(
        "  • %s → %s [%s]",
        entry.hl_group or "none",
        entry.hl_group_link or "none",
        entry.lang or "?"
      )
      add_line(text)
    end
    add_line("")
  end

  -- Semantic tokens
  if inspect_info.semantic_tokens and #inspect_info.semantic_tokens > 0 then
    add_line("Semantic Tokens", "@function.lua")
    for _, entry in ipairs(inspect_info.semantic_tokens) do
      local text = string.format(
        "  • %s → %s (p:%d)",
        entry.opts.hl_group or "none",
        entry.opts.hl_group_link or "none",
        entry.opts.priority or 0
      )
      add_line(text)
    end
    add_line("")
  end

  -- Extmarks
  if inspect_info.extmarks and #inspect_info.extmarks > 0 then
    add_line("Extmarks", "@function.lua")
    for _, entry in ipairs(inspect_info.extmarks) do
      local text = "  • " .. (entry.opts.hl_group or "none")
      if entry.ns and #entry.ns > 0 then
        text = text .. " [" .. entry.ns .. "]"
      end
      add_line(text)
    end
    add_line("")
  end

  -- If no info found
  if #lines == 0 then
    add_line("No highlight information found")
  end

  return lines, highlights
end

-- Apply highlights to the buffer
local function apply_highlights(highlights)
  vim.api.nvim_buf_clear_namespace(state.buf, state.ns, 0, -1)
  for _, hl in ipairs(highlights) do
    vim.api.nvim_buf_add_highlight(state.buf, state.ns, hl.hl_group, hl.line, 0, -1)
  end
end

-- Inspect at current position in a split
function M.inspect_in_split()
  init()

  local pos = vim.api.nvim_win_get_cursor(0)
  local inspect_info = vim.inspect_pos(0, pos[1] - 1, pos[2])
  local lines, highlights = format_inspect_info(inspect_info)

  -- Set buffer content
  vim.api.nvim_buf_set_lines(state.buf, 0, -1, false, lines)
  apply_highlights(highlights)

  -- Open in split
  vim.cmd("botright split")
  vim.cmd("resize " .. math.min(#lines + 2, 15))
  vim.api.nvim_win_set_buf(0, state.buf)

  -- Set window options
  vim.wo.number = false
  vim.wo.relativenumber = false
  vim.wo.signcolumn = "no"
  vim.wo.foldcolumn = "0"
  vim.wo.statusline = " Inspector (q to close)"

  -- Add quit mapping for this buffer
  vim.api.nvim_buf_set_keymap(state.buf, "n", "q", "<cmd>close<cr>", {
    noremap = true,
    silent = true,
    nowait = true,
  })
end

-- Toggle float inspector with mouse tracking
function M.toggle_float_inspector()
  init()

  -- If window exists and is valid, close it
  if state.win and vim.api.nvim_win_is_valid(state.win) then
    vim.api.nvim_win_close(state.win, true)
    state.win = nil
    vim.o.mousemoveevent = state.uses_mousemoveevent
    return
  end

  -- Enable mouse move events
  vim.o.mousemoveevent = true

  -- Create floating window
  state.win = vim.api.nvim_open_win(state.buf, false, {
    relative = "cursor",
    width = 40,
    height = 1,
    row = 1,
    col = 1,
    style = "minimal",
    focusable = false,
    border = "rounded",
    zindex = 1000,
  })

  -- Initial content
  vim.api.nvim_buf_set_lines(state.buf, 0, -1, false, { " Move mouse to inspect... " })

  -- Update content on first call
  vim.schedule(function()
    M.update_float()
  end)
end

-- Update float window content based on mouse position
function M.update_float()
  if not state.win or not vim.api.nvim_win_is_valid(state.win) then
    return "<MouseMove>"
  end

  vim.schedule(function()
    local pos = vim.fn.getmousepos()

    -- Skip if position is invalid
    if not pos.winid or pos.winid == 0 then
      return
    end

    -- Get buffer from mouse position window
    local buf = vim.api.nvim_win_get_buf(pos.winid)
    local inspect_info = vim.inspect_pos(buf, pos.line - 1, pos.column - 1)
    local lines, highlights = format_inspect_info(inspect_info)

    -- Update buffer content
    vim.api.nvim_buf_set_lines(state.buf, 0, -1, false, lines)
    apply_highlights(highlights)

    -- Calculate window size
    local width = 0
    for _, line in ipairs(lines) do
      width = math.max(width, #line)
    end
    width = math.min(width + 2, 60)
    local height = math.min(#lines, 20)

    -- Update window configuration
    local screen_height = vim.o.lines
    local screen_width = vim.o.columns
    local row = pos.screenrow
    local col = pos.screencol

    -- Adjust position to keep window on screen
    if row + height + 2 > screen_height then
      row = math.max(1, row - height - 2)
    end
    if col + width > screen_width then
      col = math.max(1, screen_width - width)
    end

    vim.api.nvim_win_set_config(state.win, {
      relative = "editor",
      row = row,
      col = col,
      width = width,
      height = height,
    })
  end)

  return "<MouseMove>"
end

-- Set up mouse move autocmd
function M.setup_mouse_tracking()
  vim.keymap.set({ "", "i" }, "<MouseMove>", M.update_float, { expr = true, silent = true })

  -- Clean up when window is closed
  vim.api.nvim_create_autocmd("WinClosed", {
    pattern = "*",
    callback = function(event)
      if state.win and tonumber(event.match) == state.win then
        state.win = nil
        vim.o.mousemoveevent = state.uses_mousemoveevent
      end
    end,
  })
end

-- Inspect under cursor (simple version)
function M.inspect_under_cursor()
  local pos = vim.api.nvim_win_get_cursor(0)
  local inspect_info = vim.inspect_pos(0, pos[1] - 1, pos[2])

  -- Quick display in echo area
  local items = {}

  if inspect_info.treesitter and #inspect_info.treesitter > 0 then
    for _, entry in ipairs(inspect_info.treesitter) do
      table.insert(items, string.format("TS: %s", entry.hl_group or "none"))
    end
  end

  if inspect_info.semantic_tokens and #inspect_info.semantic_tokens > 0 then
    for _, entry in ipairs(inspect_info.semantic_tokens) do
      table.insert(items, string.format("LSP: %s", entry.opts.hl_group or "none"))
    end
  end

  if #items > 0 then
    vim.notify(table.concat(items, " | "), vim.log.levels.INFO)
  else
    vim.notify("No highlight groups found", vim.log.levels.WARN)
  end
end

return M