sql: support int2vector::string casts properly

Previously, casting an int2vector to a string would fail to use the
special int2vector formatting (space-separated elements instead of the
normal {}-wrapped and comma-separated elements format of arrays). This
was causing issues with SQLAlchemy.

This commit solves this problem and simplifies the code by removing the
DOidWrapper usages for int2vector and oidvector, in favor of a field on
DArray that contains a custom oid. This opens the door to teaching
DArray's format method about the special formatting, rather than having
it live only in pgwire, where it fails to be useful in the cast of e.g.
casts.

Release note (sql change): casting an int2vector to a string now
produces a Postgres-compatible result.

pkg/sql/pgwire/types.go

@@ -176,21 +176,8 @@ func (b *writeBuffer) writeTextDatum(
 		b.writeFromFmtCtx(b.textFormatter)
 
 	case *tree.DArray:
-		switch d.ResolvedType().Oid() {
-		case oid.T_int2vector, oid.T_oidvector:
-			// vectors are serialized as a string of space-separated values.
-			sep := ""
-			// TODO(justin): add a test for nested arrays when #32552 is
-			// addressed.
-			for _, d := range v.Array {
-				b.textFormatter.WriteString(sep)
-				b.textFormatter.FormatNode(d)
-				sep = " "
-			}
-		default:
-			// Uses the default pgwire text format for arrays.
-			b.textFormatter.FormatNode(v)
-		}
+		// Arrays have custom formatting depending on their OID.
+		b.textFormatter.FormatNode(d)
 		b.writeFromFmtCtx(b.textFormatter)
 
 	case *tree.DOid:

pkg/sql/sem/tree/datum.go

@@ -2993,6 +2993,9 @@ type DArray struct {
 	// HasNonNulls is set to true if any of the datums within the are non-null.
 	// This is used in expression serialization (FmtParsable).
 	HasNonNulls bool
+
+	// customOid, if non-0, is the oid of this array datum.
+	customOid oid.Oid
 }
 
 // NewDArray returns a DArray containing elements of the specified type.
@@ -3026,6 +3029,12 @@ func MustBeDArray(e Expr) *DArray {
 
 // ResolvedType implements the TypedExpr interface.
 func (d *DArray) ResolvedType() *types.T {
+	switch d.customOid {
+	case oid.T_int2vector:
+		return types.Int2Vector
+	case oid.T_oidvector:
+		return types.OidVector
+	}
 	return types.MakeArray(d.ParamTyp)
 }
 
@@ -3514,13 +3523,19 @@ func NewDName(d string) Datum {
 // NewDIntVectorFromDArray is a helper routine to create a *DIntVector
 // (implemented as a *DOidWrapper) initialized from an existing *DArray.
 func NewDIntVectorFromDArray(d *DArray) Datum {
-	return wrapWithOid(d, oid.T_int2vector)
+	ret := new(DArray)
+	*ret = *d
+	ret.customOid = oid.T_int2vector
+	return ret
 }
 
 // NewDOidVectorFromDArray is a helper routine to create a *DOidVector
 // (implemented as a *DOidWrapper) initialized from an existing *DArray.
 func NewDOidVectorFromDArray(d *DArray) Datum {
-	return wrapWithOid(d, oid.T_oidvector)
+	ret := new(DArray)
+	*ret = *d
+	ret.customOid = oid.T_oidvector
+	return ret
 }
 
 // DatumTypeSize returns a lower bound on the total size of a Datum

pkg/sql/sem/tree/eval.go

@@ -3610,11 +3610,9 @@ func (expr *IndirectionExpr) Eval(ctx *EvalContext) (Datum, error) {
 	arr := MustBeDArray(d)
 
 	// VECTOR types use 0-indexing.
-	if w, ok := d.(*DOidWrapper); ok {
-		switch w.Oid {
-		case oid.T_oidvector, oid.T_int2vector:
-			subscriptIdx++
-		}
+	switch arr.customOid {
+	case oid.T_oidvector, oid.T_int2vector:
+		subscriptIdx++
 	}
 	if subscriptIdx < 1 || subscriptIdx > arr.Len() {
 		return DNull, nil

pkg/sql/sem/tree/pgwire_encode.go

@@ -15,6 +15,8 @@ package tree
 import (
 	"bytes"
 	"unicode/utf8"
+
+	"github.com/lib/pq/oid"
 )
 
 func (d *DTuple) pgwireFormat(ctx *FmtCtx) {
@@ -88,6 +90,20 @@ func (d *DArray) pgwireFormat(ctx *FmtCtx) {
 	// instead printed as-is. Only non-valid characters get escaped to
 	// hex. So we delegate this formatting to a tuple-specific
 	// string printer called pgwireFormatStringInArray().
+	switch d.ResolvedType().Oid() {
+	case oid.T_int2vector, oid.T_oidvector:
+		// vectors are serialized as a string of space-separated values.
+		sep := ""
+		// TODO(justin): add a test for nested arrays when #32552 is
+		// addressed.
+		for _, d := range d.Array {
+			ctx.WriteString(sep)
+			ctx.FormatNode(d)
+			sep = " "
+		}
+		return
+	}
+
 	ctx.WriteByte('{')
 	comma := ""
 	for _, v := range d.Array {