tree-sitter: split tree-sitter lua interface from demo code

runtime/lua/vim/tree_sitter.lua

@@ -0,0 +1,47 @@
+local a = vim.api
+
+function parse_tree(tsstate, force)
+  if tsstate.valid and not force then
+    return tsstate.tree
+  end
+  tsstate.tree = tsstate.parser:parse_buf(tsstate.bufnr)
+  tsstate.valid = true
+  return tsstate.tree
+end
+
+local function change_cb(tsstate, ev, bufnr, tick, start_row, oldstopline, stop_row)
+  local start_byte = a.nvim_buf_get_offset(bufnr,start_row)
+  -- a bit messy, should we expose edited but not reparsed tree?
+  -- are multiple edits safe in general?
+  local root = tsstate.parser:tree():root()
+  -- TODO: add proper lookup function!
+  local inode = root:descendant_for_point_range(oldstopline+9000,0, oldstopline,0)
+  if inode == nil then
+    local stop_byte = a.nvim_buf_get_offset(bufnr,stop_row)
+    tsstate.parser:edit(start_byte,stop_byte,stop_byte,start_row,0,stop_row,0,stop_row,0)
+  else
+    local fakeoldstoprow, fakeoldstopcol, fakebyteoldstop = inode:start()
+    local fake_rows = fakeoldstoprow-oldstopline
+    local fakestop = stop_row+fake_rows
+    local fakebytestop = a.nvim_buf_get_offset(bufnr,fakestop)+fakeoldstopcol
+    tsstate.parser:edit(start_byte,fakebyteoldstop,fakebytestop,start_row,0,fakeoldstoprow,fakeoldstopcol,fakestop,fakeoldstopcol)
+  end
+  tsstate.valid = false
+end
+
+function create_parser(bufnr)
+  if bufnr == 0 then
+    bufnr = a.nvim_get_current_buf()
+  end
+  local ft = a.nvim_buf_get_option(bufnr, "filetype")
+  local tsstate = {}
+  tsstate.bufnr = bufnr
+  tsstate.parser = vim.ts_parser(ft.."_parser.so", ft)
+  parse_tree(tsstate)
+  local function cb(ev, ...)
+    return change_cb(tsstate, ev, ...)
+  end
+  a.nvim_buf_attach(tsstate.bufnr, false, {on_lines=cb})
+  return tsstate
+end
+