Fix parsing of complex morphs to tsquery

When to_tsquery() or websearch_to_tsquery() meet a complex morph containing
multiple words residing adjacent position, these words are connected
with OP_AND operator.  That leads to surprising results.  For instace,
both websearch_to_tsquery('"pg_class pg"') and to_tsquery('pg_class <-> pg')
produce '( pg & class ) <-> pg' tsquery.  This tsquery requires
'pg' and 'class' words to reside on the same position and doesn't match
to to_tsvector('pg_class pg').  It appears to be ridiculous behavior, which
needs to be fixed.

This commit makes to_tsquery() or websearch_to_tsquery() connect words
residing adjacent position with OP_PHRASE.  Therefore, now those words are
normally chained with other OP_PHRASE operator.  The examples of above now
produces 'pg <-> class <-> pg' tsquery, which matches to
to_tsvector('pg_class pg').

Another effect of this commit is that complex morph word positions now need to
match the tsvector even if there is no surrounding OP_PHRASE.  This behavior
change generally looks like an improvement but making this commit not
backpatchable.

Reported-by: Barry Pederson
Bug: #16592
Discussion: https://postgr.es/m/16592-70b110ff9731c07d@postgresql.org
Discussion: https://postgr.es/m/CAPpHfdv0EzVhf6CWfB1_TTZqXV_2Sn-jSY3zSd7ePH%3D-%2B1V2DQ%40mail.gmail.com
Author: Alexander Korotkov
Reviewed-by: Tom Lane, Neil Chen

1 files changed, 38 insertions, 3 deletions

diff --git a/src/backend/tsearch/to_tsany.c b/src/backend/tsearch/to_tsany.c
index e4ad661a8ba..f4ddfc01059 100644
--- a/src/backend/tsearch/to_tsany.c
+++ b/src/backend/tsearch/to_tsany.c
@@ -20,10 +20,20 @@
 #include "utils/jsonfuncs.h"
 
 
+/*
+ * Opaque data structure, which is passed by parse_tsquery() to pushval_morph().
+ */
 typedef struct MorphOpaque
 {
 	Oid			cfg_id;
-	int			qoperator;		/* query operator */
+
+	/*
+	 * Single tsquery morph could be parsed into multiple words.  When these
+	 * words reside in adjacent positions, they are connected using this
+	 * operator.  Usually, that is OP_PHRASE, which requires word positions of
+	 * a complex morph to exactly match the tsvector.
+	 */
+	int			qoperator;
 } MorphOpaque;
 
 typedef struct TSVectorBuildState
@@ -573,7 +583,14 @@ to_tsquery_byid(PG_FUNCTION_ARGS)
 	MorphOpaque data;
 
 	data.cfg_id = PG_GETARG_OID(0);
-	data.qoperator = OP_AND;
+
+	/*
+	 * Passing OP_PHRASE as a qoperator makes tsquery require matching of word
+	 * positions of a complex morph exactly match the tsvector.  Also, when
+	 * the complex morphs are connected with OP_PHRASE operator, we connect
+	 * all their words into the OP_PHRASE sequence.
+	 */
+	data.qoperator = OP_PHRASE;
 
 	query = parse_tsquery(text_to_cstring(in),
 						  pushval_morph,
@@ -603,6 +620,12 @@ plainto_tsquery_byid(PG_FUNCTION_ARGS)
 	MorphOpaque data;
 
 	data.cfg_id = PG_GETARG_OID(0);
+
+	/*
+	 * parse_tsquery() with P_TSQ_PLAIN flag takes the whole input text as a
+	 * single morph.  Passing OP_PHRASE as a qoperator makes tsquery require
+	 * matching of all words independently on their positions.
+	 */
 	data.qoperator = OP_AND;
 
 	query = parse_tsquery(text_to_cstring(in),
@@ -634,6 +657,12 @@ phraseto_tsquery_byid(PG_FUNCTION_ARGS)
 	MorphOpaque data;
 
 	data.cfg_id = PG_GETARG_OID(0);
+
+	/*
+	 * parse_tsquery() with P_TSQ_PLAIN flag takes the whole input text as a
+	 * single morph.  Passing OP_PHRASE as a qoperator makes tsquery require
+	 * matching of word positions.
+	 */
 	data.qoperator = OP_PHRASE;
 
 	query = parse_tsquery(text_to_cstring(in),
@@ -665,7 +694,13 @@ websearch_to_tsquery_byid(PG_FUNCTION_ARGS)
 
 	data.cfg_id = PG_GETARG_OID(0);
 
-	data.qoperator = OP_AND;
+	/*
+	 * Passing OP_PHRASE as a qoperator makes tsquery require matching of word
+	 * positions of a complex morph exactly match the tsvector.  Also, when
+	 * the complex morphs are given in quotes, we connect all their words into
+	 * the OP_PHRASE sequence.
+	 */
+	data.qoperator = OP_PHRASE;
 
 	query = parse_tsquery(text_to_cstring(in),
 						  pushval_morph,