pg_catalog: indoption was not encoded correctly

Previously, the indoption field inside pg_index was encoded incorrectly,
which could cause problems for binary clients. Specifically, an int8 was
being sent across the wire, then int2vectors are supposed to be made of
int2. To address this, this patch ensures that an int2 is used and adds
assertion inside the conversion code (for int2vector) to avoid future
problems.

Fixes: cockroachdb#111907

Release note (bug fix): indoption inside pg_index was not properly
encoded, causing clients to be unable to decode it as int2vector.

pkg/sql/pg_catalog.go

@@ -1879,7 +1879,7 @@ https://www.postgresql.org/docs/9.5/catalog-pg-index.html`,
 					// Also fill in indoption for each column to indicate if the index
 					// is ASC/DESC and if nulls appear first/last.
 					collationOids := tree.NewDArray(types.Oid)
-					indoption := tree.NewDArray(types.Int)
+					indoption := tree.NewDArray(types.Int2)
 
 					colAttNums := make([]descpb.ColumnID, 0, index.NumKeyColumns())
 					exprs := make([]string, 0, index.NumKeyColumns())

pkg/sql/sem/tree/datum.go

@@ -5922,6 +5922,10 @@ func NewDName(d string) Datum {
 // NewDIntVectorFromDArray is a helper routine to create a new *DArray,
 // initialized from an existing *DArray, with the special oid for IntVector.
 func NewDIntVectorFromDArray(d *DArray) Datum {
+	// Sanity: Validate the type of the array, since it should be int2.
+	if d.ParamTyp != types.Int2 {
+		panic(errors.AssertionFailedf("int2vector can only be made from int2 not %v", d.ParamTyp))
+	}
 	ret := new(DArray)
 	*ret = *d
 	ret.customOid = oid.T_int2vector