Tweak BRIN minmax operator class

In the union support proc, we were not checking the hasnulls flag of
value A early enough, so it could be skipped if the "allnulls" flag in
value B is set.  Also, a check on the allnulls flag of value "B" was
redundant, so remove it.

Also change inet_minmax_ops to not be the default opclass for type inet,
as a future inclusion operator class would be more useful and it's
pretty difficult to change default opclass for a datatype later on.
(There is no catversion bump for this catalog change; this shouldn't be
a problem.)

Extracted from a larger patch to add an "inclusion" operator class.

Author: Emre Hasegeli

src/backend/access/brin/brin_minmax.c

@@ -256,23 +256,24 @@ brin_minmax_union(PG_FUNCTION_ARGS)
 
 	Assert(col_a->bv_attno == col_b->bv_attno);
 
-	/* If there are no values in B, there's nothing to do */
+	/* Adjust "hasnulls" */
+	if (!col_a->bv_hasnulls && col_b->bv_hasnulls)
+		col_a->bv_hasnulls = true;
+
+	/* If there are no values in B, there's nothing left to do */
 	if (col_b->bv_allnulls)
 		PG_RETURN_VOID();
 
 	attno = col_a->bv_attno;
 	attr = bdesc->bd_tupdesc->attrs[attno - 1];
 
-	/* Adjust "hasnulls" */
-	if (col_b->bv_hasnulls && !col_a->bv_hasnulls)
-		col_a->bv_hasnulls = true;
-
 	/*
-	 * Adjust "allnulls".  If B has values but A doesn't, just copy the values
-	 * from B into A, and we're done.  (We cannot run the operators in this
-	 * case, because values in A might contain garbage.)
+	 * Adjust "allnulls".  If A doesn't have values, just copy the values
+	 * from B into A, and we're done.  We cannot run the operators in this
+	 * case, because values in A might contain garbage.  Note we already
+	 * established that B contains values.
 	 */
-	if (!col_b->bv_allnulls && col_a->bv_allnulls)
+	if (col_a->bv_allnulls)
 	{
 		col_a->bv_allnulls = false;
 		col_a->bv_values[0] = datumCopy(col_b->bv_values[0],

src/include/catalog/pg_opclass.h

@@ -252,7 +252,7 @@ DATA(insert (	3580	float8_minmax_ops		PGNSP PGUID 4070   701 t 0 ));
 DATA(insert (	3580	abstime_minmax_ops		PGNSP PGUID 4072   702 t 0 ));
 DATA(insert (	3580	reltime_minmax_ops		PGNSP PGUID 4073   703 t 0 ));
 DATA(insert (	3580	macaddr_minmax_ops		PGNSP PGUID 4074   829 t 0 ));
-DATA(insert (	3580	inet_minmax_ops			PGNSP PGUID 4075   869 t 0 ));
+DATA(insert (	3580	inet_minmax_ops			PGNSP PGUID 4075   869 f 0 ));
 DATA(insert (	3580	bpchar_minmax_ops		PGNSP PGUID 4076  1042 t 0 ));
 DATA(insert (	3580	time_minmax_ops			PGNSP PGUID 4077  1083 t 0 ));
 DATA(insert (	3580	date_minmax_ops			PGNSP PGUID 4059  1082 t 0 ));

src/test/regress/expected/brin.out

@@ -65,7 +65,7 @@ CREATE INDEX brinidx ON brintest USING brin (
 	float4col,
 	float8col,
 	macaddrcol,
-	inetcol,
+	inetcol inet_minmax_ops,
 	bpcharcol,
 	datecol,
 	timecol,

src/test/regress/sql/brin.sql

@@ -68,7 +68,7 @@ CREATE INDEX brinidx ON brintest USING brin (
 	float4col,
 	float8col,
 	macaddrcol,
-	inetcol,
+	inetcol inet_minmax_ops,
 	bpcharcol,
 	datecol,
 	timecol,