feat: highlight code chunks in quarto ft

without plugins

ftplugin/quarto.lua

@@ -1,3 +1,6 @@
+local api = vim.api
+local ts = vim.treesitter
+
 vim.b.slime_cell_delimiter = '```'
 vim.b['quarto_is_r_mode'] = nil
 vim.b['reticulate_running'] = false
@@ -13,7 +16,61 @@ vim.wo.showbreak = '|'
 vim.api.nvim_buf_set_var(0, 'did_ftplugin', true)
 
 -- markdown vs. quarto hacks
-local ns = vim.api.nvim_create_namespace 'quartoHighlight'
+local ns = vim.api.nvim_create_namespace 'QuartoHighlight'
 vim.api.nvim_set_hl(ns, '@markup.strikethrough', { strikethrough = false })
 vim.api.nvim_set_hl(ns, '@markup.doublestrikethrough', { strikethrough = true })
 vim.api.nvim_win_set_hl_ns(0, ns)
+
+-- highlight code cells similar to
+-- 'lukas-reineke/headlines.nvim'
+-- (disabled in lua/plugins/ui.lua)
+local buf = api.nvim_get_current_buf()
+
+local parsername = 'markdown'
+local parser = ts.get_parser(buf, parsername)
+local tsquery = '(fenced_code_block)@codecell'
+
+-- vim.api.nvim_set_hl(0, '@markup.codecell', { bg = '#000055' })
+vim.api.nvim_set_hl(0, '@markup.codecell', {
+  link = 'CursorLine',
+})
+
+local function clear_all()
+  local all = api.nvim_buf_get_extmarks(buf, ns, 0, -1, {})
+  for _, mark in ipairs(all) do
+    vim.api.nvim_buf_del_extmark(buf, ns, mark[1])
+  end
+end
+
+local function highlight_range(from, to)
+  for i = from, to do
+    vim.api.nvim_buf_set_extmark(buf, ns, i, 0, {
+      hl_eol = true,
+      line_hl_group = '@markup.codecell',
+    })
+  end
+end
+
+local function highlight_cells()
+  clear_all()
+
+  local query = ts.query.parse(parsername, tsquery)
+  local tree = parser:parse()
+  local root = tree[1]:root()
+  for _, match, _ in query:iter_matches(root, buf, 0, -1, { all = true }) do
+    for _, nodes in pairs(match) do
+      for _, node in ipairs(nodes) do
+        local start_line, _, end_line, _ = node:range()
+        pcall(highlight_range, start_line, end_line - 1)
+      end
+    end
+  end
+end
+
+highlight_cells()
+
+vim.api.nvim_create_autocmd({ 'ModeChanged', 'BufWrite' }, {
+  group = vim.api.nvim_create_augroup('QuartoCellHighlight', { clear = true }),
+  buffer = buf,
+  callback = highlight_cells,
+})