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.

src/backend/utils/adt/tsvector_op.c

@@ -1276,12 +1276,13 @@ 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,
@@ -1347,6 +1348,11 @@ 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
 			{

src/test/regress/expected/tstypes.out

@@ -533,6 +533,24 @@ SELECT 'a b:89  ca:23A,64c cb:80b d:34c'::tsvector @@ 'd:AC & c:*B' as "true";
  t
 (1 row)
 
+SELECT 'wa:1D wb:2A'::tsvector @@ 'w:*D & w:*A'::tsquery as "true";
+ true 
+------
+ t
+(1 row)
+
+SELECT 'wa:1D wb:2A'::tsvector @@ 'w:*D <-> w:*A'::tsquery as "true";
+ true 
+------
+ t
+(1 row)
+
+SELECT 'wa:1A wb:2D'::tsvector @@ 'w:*D <-> w:*A'::tsquery as "false";
+ false 
+-------
+ f
+(1 row)
+
 SELECT 'supernova'::tsvector @@ 'super'::tsquery AS "false";
  false 
 -------

src/test/regress/sql/tstypes.sql

@@ -101,6 +101,9 @@ SELECT 'a b:89  ca:23A,64b d:34c'::tsvector @@ 'd:AC & c:*CB' as "true";
 SELECT 'a b:89  ca:23A,64b cb:80c d:34c'::tsvector @@ 'd:AC & c:*C' as "true";
 SELECT 'a b:89  ca:23A,64c cb:80b d:34c'::tsvector @@ 'd:AC & c:*C' as "true";
 SELECT 'a b:89  ca:23A,64c cb:80b d:34c'::tsvector @@ 'd:AC & c:*B' as "true";
+SELECT 'wa:1D wb:2A'::tsvector @@ 'w:*D & w:*A'::tsquery as "true";
+SELECT 'wa:1D wb:2A'::tsvector @@ 'w:*D <-> w:*A'::tsquery as "true";
+SELECT 'wa:1A wb:2D'::tsvector @@ 'w:*D <-> w:*A'::tsquery as "false";
 
 SELECT 'supernova'::tsvector @@ 'super'::tsquery AS "false";
 SELECT 'supeanova supernova'::tsvector @@ 'super'::tsquery AS "false";