Don't store empty segments. When inserting empty strings, the code

was writing out a segment made up of a single leaf node containing the
\0 header.  LeafReader assumed that leaf nodes always contained at
least one term, so assertions would fail.

While it would be possible to support reading and merging empty
segments, there's no reason to do so.  While this change could have
been done in writeZeroSegment(), I put it in leafWriterFlush() so that
it would work right if segmentMerge() created an empty segment, which
could happen with future changes to how deleted documents are handled. (CVS 3484)

FossilOrigin-Name: fed79beec7da24a26ae94494bdc0c98dd102bc06

ext/fts2/fts2.c

@@ -3785,6 +3785,9 @@ static int leafWriterFlush(fulltext_vtab *v, LeafWriter *pWriter){
   rc = leafWriterRootInfo(v, pWriter, &pRootInfo, &nRootInfo, &iEndBlockid);
   if( rc!=SQLITE_OK ) return rc;
 
+  /* Don't bother storing an entirely empty segment. */
+  if( iEndBlockid==0 && nRootInfo==1 ) return SQLITE_OK;
+
   return segdir_set(v, pWriter->iLevel, pWriter->idx,
                     pWriter->iStartBlockid, pWriter->iEndBlockid,
                     iEndBlockid, pRootInfo, nRootInfo);

manifest

@@ -1,5 +1,5 @@
-C dup\sfts1\stests\sand\sedit\sfor\sfts2.\s\sfts1porter.test\somitted\sbecause\sit\ndepends\son\sbeing\sable\sto\spoke\sthrough\sto\s%_term\stable.\s(CVS\s3482)
-D 2006-10-19T23:36:26
+C Don't\sstore\sempty\ssegments.\s\sWhen\sinserting\sempty\sstrings,\sthe\scode\nwas\swriting\sout\sa\ssegment\smade\sup\sof\sa\ssingle\sleaf\snode\scontaining\sthe\n\\0\sheader.\s\sLeafReader\sassumed\sthat\sleaf\snodes\salways\scontained\sat\nleast\sone\sterm,\sso\sassertions\swould\sfail.\n\nWhile\sit\swould\sbe\spossible\sto\ssupport\sreading\sand\smerging\sempty\nsegments,\sthere's\sno\sreason\sto\sdo\sso.\s\sWhile\sthis\schange\scould\shave\nbeen\sdone\sin\swriteZeroSegment(),\sI\sput\sit\sin\sleafWriterFlush()\sso\sthat\nit\swould\swork\sright\sif\ssegmentMerge()\screated\san\sempty\ssegment,\swhich\ncould\shappen\swith\sfuture\schanges\sto\show\sdeleted\sdocuments\sare\shandled.\s(CVS\s3484)
+D 2006-10-25T05:21:55
 F Makefile.in 4379c909d46b38b8c5db3533084601621d4f14b2
 F Makefile.linux-gcc 2d8574d1ba75f129aba2019f0b959db380a90935
 F README 9c4e2d6706bdcc3efdd773ce752a8cdab4f90028
@@ -33,7 +33,7 @@ F ext/fts1/fulltext.h 08525a47852d1d62a0be81d3fc3fe2d23b094efd
 F ext/fts1/simple_tokenizer.c 1844d72f7194c3fd3d7e4173053911bf0661b70d
 F ext/fts1/tokenizer.h 0c53421b832366d20d720d21ea3e1f6e66a36ef9
 F ext/fts2/README.txt 8c18f41574404623b76917b9da66fcb0ab38328d
-F ext/fts2/fts2.c ddfca6aecbc5cbf13633f92aac29c2a8f24d6dec
+F ext/fts2/fts2.c 8f5e5fccec924c13c5e36382ddabf8a0bf075859
 F ext/fts2/fts2.h bbdab26d34f91974d5b9ade8b7836c140a7c4ce1
 F ext/fts2/fts2_hash.c b3f22116d4ef0bc8f2da6e3fdc435c86d0951a9b
 F ext/fts2/fts2_hash.h e283308156018329f042816eb09334df714e105e
@@ -418,7 +418,7 @@ F www/tclsqlite.tcl bb0d1357328a42b1993d78573e587c6dcbc964b9
 F www/vdbe.tcl 87a31ace769f20d3627a64fa1fade7fed47b90d0
 F www/version3.tcl 890248cf7b70e60c383b0e84d77d5132b3ead42b
 F www/whentouse.tcl 97e2b5cd296f7d8057e11f44427dea8a4c2db513
-P b01c4371d861a087623a34c38cb8db74eca95348
-R c24a94afe5bc7f2d9a795aaefd9ab181
+P 2806c3415841b98d52163fa672a747d0a47ffd41
+R 5cdccaf3295b3f3b1078e6d0239b59c8
 U shess
-Z ebbb22449f830ff82b909fcef8d93031
+Z 9691b521636d92a41ca36d38cbd27e9e

manifest.uuid

@@ -1 +1 @@
-2806c3415841b98d52163fa672a747d0a47ffd41
+fed79beec7da24a26ae94494bdc0c98dd102bc06