configuration file parsing fails when content_by_lua_block has long string

version: openresty/1.15.8.2

It's ok to have short lua string inside content_by_lua_block:

location / {
  content_by_lua_block {
    local s = [[aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa]]
  }
}

But if the string is long enough, more than 4000 in my case, configuration parsing fails:

location / {
  content_by_lua_block {
    local s = [[aaaaaaaaaa(many many characters, more than 4000 as)aaaaaaaaaaaaaaaaaaaaaa]]
  }
}

$ sbin/nginx -t
2020/02/12 15:20:29 [emerg] 56#56: Lua code block missing the closing long bracket "]]" in /usr/local/openresty/nginx/conf/nginx.conf:22
nginx: [emerg] Lua code block missing the closing long bracket "]]" in /usr/local/openresty/nginx/conf/nginx.conf:22
nginx: configuration file /usr/local/openresty/nginx/conf/nginx.conf test failed

Reproduce the failure with the content_by_lua_block example in nginx.conf and run sbin/nginx -t. Trace the configuration parsing entry point for content_by_lua_block, then verify that a Lua long string exceeding 4000 characters parses successfully and that the configuration test passes.