Solr 7.7 UpdateRequestProcessor broken

[Andreas Hubold]

Hi,

while trying to update from Solr 7.6 to 7.7 I run into some unexpected 
incompatibilites with UpdateRequestProcessors.

The SolrInputDocument passed to UpdateRequestProcessor#processAdd does 
not return Strings for string fields anymore but instances of 
org.apache.solr.common.util.ByteArrayUtf8CharSequence. I found some 
related JIRA issues (SOLR-12983?) but nothing under the "Upgrade Notes" 
section.

I can adapt our UpdateRequestProcessor implementations but at least the 
org.apache.solr.update.processor.LangDetectLanguageIdentifierUpdateProcessor 
is broken now as well and needs to be fixed in Solr. It expects String 
values and logs messages such as the following now:

2019-02-14 13:14:47.537 WARN  (qtp802600647-19) [   x:studio] 
o.a.s.u.p.LangDetectLanguageIdentifierUpdateProcessor Field 
name_tokenized not a String value, not including in detection

I wonder what kind of plugins are affected by the change. Does this only 
affect UpdateRequestProcessors or more plugins? Do I need to handle 
these ByteArrayUtf8CharSequence instances in SolrJ clients now as well?

Cheers,
Andreas