feat(treesitter): add foldtext with treesitter highlighting (#25391)

1 files changed, 92 insertions, 0 deletions

diff --git a/runtime/lua/vim/treesitter/_fold.lua b/runtime/lua/vim/treesitter/_fold.lua
index 8bc08c9c2e..c6a4b48d4f 100644
--- a/runtime/lua/vim/treesitter/_fold.lua
+++ b/runtime/lua/vim/treesitter/_fold.lua
@@ -361,4 +361,96 @@ function M.foldexpr(lnum)
   return foldinfos[bufnr].levels[lnum] or '0'
 end
 
+---@package
+---@return { [1]: string, [2]: string[] }[]|string
+function M.foldtext()
+  local foldstart = vim.v.foldstart
+  local bufnr = api.nvim_get_current_buf()
+
+  ---@type boolean, LanguageTree
+  local ok, parser = pcall(ts.get_parser, bufnr)
+  if not ok then
+    return vim.fn.foldtext()
+  end
+
+  local query = ts.query.get(parser:lang(), 'highlights')
+  if not query then
+    return vim.fn.foldtext()
+  end
+
+  local tree = parser:parse({ foldstart - 1, foldstart })[1]
+
+  local line = api.nvim_buf_get_lines(bufnr, foldstart - 1, foldstart, false)[1]
+  if not line then
+    return vim.fn.foldtext()
+  end
+
+  ---@type { [1]: string, [2]: string[], range: { [1]: integer, [2]: integer } }[] | { [1]: string, [2]: string[] }[]
+  local result = {}
+
+  local line_pos = 0
+
+  for id, node, metadata in query:iter_captures(tree:root(), 0, foldstart - 1, foldstart) do
+    local name = query.captures[id]
+    local start_row, start_col, end_row, end_col = node:range()
+
+    local priority = tonumber(metadata.priority or vim.highlight.priorities.treesitter)
+
+    if start_row == foldstart - 1 and end_row == foldstart - 1 then
+      -- check for characters ignored by treesitter
+      if start_col > line_pos then
+        table.insert(result, {
+          line:sub(line_pos + 1, start_col),
+          { { 'Folded', priority } },
+          range = { line_pos, start_col },
+        })
+      end
+      line_pos = end_col
+
+      local text = line:sub(start_col + 1, end_col)
+      table.insert(result, { text, { { '@' .. name, priority } }, range = { start_col, end_col } })
+    end
+  end
+
+  local i = 1
+  while i <= #result do
+    -- find first capture that is not in current range and apply highlights on the way
+    local j = i + 1
+    while
+      j <= #result
+      and result[j].range[1] >= result[i].range[1]
+      and result[j].range[2] <= result[i].range[2]
+    do
+      for k, v in ipairs(result[i][2]) do
+        if not vim.tbl_contains(result[j][2], v) then
+          table.insert(result[j][2], k, v)
+        end
+      end
+      j = j + 1
+    end
+
+    -- remove the parent capture if it is split into children
+    if j > i + 1 then
+      table.remove(result, i)
+    else
+      -- highlights need to be sorted by priority, on equal prio, the deeper nested capture (earlier
+      -- in list) should be considered higher prio
+      if #result[i][2] > 1 then
+        table.sort(result[i][2], function(a, b)
+          return a[2] < b[2]
+        end)
+      end
+
+      result[i][2] = vim.tbl_map(function(tbl)
+        return tbl[1]
+      end, result[i][2])
+      result[i] = { result[i][1], result[i][2] }
+
+      i = i + 1
+    end
+  end
+
+  return result
+end
+
 return M