Fix YA text phrase search bug.

checkcondition_str() failed to report multiple matches for a prefix
pattern correctly: it would dutifully merge the match positions, but
then after exiting that loop, if the last prefix-matching word had
had no suitable positions, it would report there were no matches.
The upshot would be failing to recognize a match that the query
should match.

It looks like you need all of these conditions to see the bug:
* a phrase search (else we don't ask for match position details)
* a prefix search item (else we don't get to this code)
* a weight restriction (else checkclass_str won't fail)

Noted while investigating a problem report from Pavel Borisov,
though this is distinct from the issue he was on about.

Back-patch to 9.6 where phrase search was added.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/backend/utils/adt/tsvector_op.c b/src/backend/utils/adt/tsvector_op.c
index d571b93ddb8..5dc988f139b 100644
--- a/src/backend/utils/adt/tsvector_op.c
+++ b/src/backend/utils/adt/tsvector_op.c
@@ -1326,12 +1326,13 @@ checkcondition_str(void *checkval, QueryOperand *val, ExecPhraseData *data)
 	WordEntry  *StopLow = chkval->arrb;
 	WordEntry  *StopHigh = chkval->arre;
 	WordEntry  *StopMiddle = StopHigh;
-	int			difference = -1;
 	bool		res = false;
 
 	/* Loop invariant: StopLow <= val < StopHigh */
 	while (StopLow < StopHigh)
 	{
+		int			difference;
+
 		StopMiddle = StopLow + (StopHigh - StopLow) / 2;
 		difference = tsCompareString(chkval->operand + val->distance,
 									 val->length,
@@ -1397,6 +1398,11 @@ checkcondition_str(void *checkval, QueryOperand *val, ExecPhraseData *data)
 					memcpy(allpos + npos, data->pos, sizeof(WordEntryPos) * data->npos);
 					npos += data->npos;
 				}
+				else
+				{
+					/* at loop exit, res must be true if we found matches */
+					res = (npos > 0);
+				}
 			}
 			else
 			{