So, without rancour or antipathy, I ask the entire list: has ANYONE gotten a
Dovecot/solr-fts-plugin setup to work that provides as a BASELINE, all of the
following functionality:

1) The ability to search for a string within any of the structured fields
(from/subject) that returns correct results?

Yes.

2) The ability to search for any string within the BODY of emails, including
the MIME attachment boundaries?

Yes.

3) The ability to do "ranging" searches for structures within emails that
decompose to "dates" or other simple-numeric data?

Dunno - I don't think I've needed that and I'm not sure how to do it.  My mail clients are Thunderbird and AquaMail (on Android).  If you'll give me either the desired Thunderbird steps or telnet-based IMAP command I'm happy to test.

OPTIONALLY, and this is probably way outside of the scope of the above,
despite the fact that it's listed as a "selling point" of SOLR versus other
full text search engines:

4) The ability to do searches against any attachments that are able to be
post-processed and hyper-indexed by SOLR+Tika?

Haven't tried.

SOLR seems to have "brand cachet", so presumably it actually works (for somebody).

It works - just sometimes needs more effort to setup than it should.

Dovecot has not a little "brand cachet", and for me, I have innate faith and
trust in Timo and his software.

I think we're all in agreement here.

But please, level with us faithful users.  Does this morass of Java B.S.
actually work, and if not, please just deprecate and remove this moribund
software, and stop trying to bury the only FTS plugin many of us HAVE actually
gotten to work.  (Pretty please?)

I respect that Messr. Moreau has made an earnest effort to get this JAVA B.S.
to actually work, as I have. 

He persevered where I'd given up. He's vocal about it, and now I'm chiming in
that this ornate collection of switchblades only cuts those who try to use them.

Short answer - it actually works.  Longer answer - I've gone through a hate/love/hate/like relationship with Solr myself.  The transition from v3 to v4 was a major headache - and I gave up for a while.  But versions 6 & 7 have been pretty good for me.  I'm neither a Dovecot nor a Solr developer - just enough of a fiddler to get them working to fulfill my own needs.

If my unreliable memory serves I believe the Dovecot fts-solr plugin hasn't needed to change much (I recall one significant change required when Solr changed it's protocol - I think an XML/JSON thing).  So having a stable interface let's Timo & Co. forget about on-going FTS development and continue focusing on things not provided by other tools.  Hopefully they'll revisit SIS...

I recall reading something about the Lucene library (which Squat & Solr are based on) and again my memory is the C version(s) weren't getting maintained as well as might be desired.  I think having the Solr/Lucene team focusing on Java development was another point of consideration for Dovecot's squat - but I could be totally off here.

Based on the errors reported by Joan I believe that system's problems are due to configuration - either Solr, Dovecot, or both.  They don't sound like Java related issues (which are a *major* pain to deal with!).  I've provided a copy of what is a working configuration *for me*.  I'm happy to continue helping as best I can - and if Joan, you, or anyone else would like my aid I'll do my best.  If you're crazy I-mean-trusting enough to have me SSH or remote view to your system I'm willing to take a look.  I've had enough people help me over the years for various packages that I'd like to pay it forward where I can.

--
Daniel