sql: populate the pg_enum catalog table

Fixes #48359.

Release note (sql change): Populate the catalog table
`pg_catalog.pg_enum`.

pkg/sql/logictest/testdata/logic_test/pg_catalog

@@ -916,13 +916,22 @@ JOIN pg_constraint ON objid=pg_constraint.oid AND refobjid=pg_constraint.conindi
 contype
 f
 
-## pg_catalog.pg_type
-
-# Create some user defined types for testing.
+## pg_catalog.pg_enum
 statement ok
 CREATE TYPE newtype1 AS ENUM ('v1', 'v2');
 CREATE TYPE newtype2 AS ENUM ('v3', 'v4')
 
+query OORT colnames
+SELECT * FROM pg_enum
+----
+oid  enumtypid  enumsortorder  enumlabel
+1043025669  100063  0  v1
+1043025861  100063  1  v2
+1865129000  100064  0  v3
+1865129192  100064  1  v4
+
+## pg_catalog.pg_type
+
 query OTOOIBT colnames
 SELECT oid, typname, typnamespace, typowner, typlen, typbyval, typtype
 FROM pg_catalog.pg_type
@@ -1626,13 +1635,6 @@ SELECT objoid, classoid, description FROM pg_catalog.pg_shdescription
 ----
 objoid  classoid  description
 
-## pg_catalog.pg_enum
-
-query OORT colnames
-SELECT * FROM pg_catalog.pg_enum
-----
-oid  enumtypid  enumsortorder  enumlabel
-
 ## pg_catalog.pg_event_trigger
 
 query TTOOTT colnames

pkg/sql/pg_catalog.go

@@ -1436,8 +1436,43 @@ CREATE TABLE pg_catalog.pg_enum (
   enumsortorder FLOAT4,
   enumlabel STRING
 )`,
-	populate: func(_ context.Context, p *planner, _ *DatabaseDescriptor, addRow func(...tree.Datum) error) error {
-		// Enum types are not currently supported.
+	populate: func(ctx context.Context, p *planner, dbContext *DatabaseDescriptor, addRow func(...tree.Datum) error) error {
+		h := makeOidHasher()
+		descs, err := p.Tables().getAllDescriptors(ctx, p.txn)
+		if err != nil {
+			return err
+		}
+		for _, desc := range descs {
+			typDesc, ok := desc.(*sqlbase.TypeDescriptor)
+			if !ok {
+				continue
+			}
+			if dbContext != nil && typDesc.ParentID != dbContext.ID {
+				continue
+			}
+			if typDesc.Kind != sqlbase.TypeDescriptor_ENUM {
+				continue
+			}
+			// Generate a row for each member of the enum. We don't represent enums
+			// internally using floats for ordering like Postgres, so just pick a
+			// float entry for the rows.
+			typ := types.MakeEnum(uint32(typDesc.ID))
+			if err := typDesc.HydrateTypeInfo(typ); err != nil {
+				return err
+			}
+			enumData := typ.TypeMeta.EnumData
+			typOID := tree.NewDOid(tree.DInt(typ.Oid()))
+			for i := range enumData.LogicalRepresentations {
+				if err := addRow(
+					h.EnumEntryOid(typOID, enumData.PhysicalRepresentations[i]),
+					typOID,
+					tree.NewDFloat(tree.DFloat(float64(i))),
+					tree.NewDString(enumData.LogicalRepresentations[i]),
+				); err != nil {
+					return err
+				}
+			}
+		}
 		return nil
 	},
 }
@@ -3098,6 +3133,12 @@ func (h oidHasher) writeStr(s string) {
 	}
 }
 
+func (h oidHasher) writeBytes(b []byte) {
+	if _, err := h.h.Write(b); err != nil {
+		panic(err)
+	}
+}
+
 func (h oidHasher) writeUInt8(i uint8) {
 	if err := binary.Write(h.h, binary.BigEndian, i); err != nil {
 		panic(err)
@@ -3135,6 +3176,7 @@ const (
 	userTypeTag
 	collationTypeTag
 	operatorTypeTag
+	enumEntryTypeTag
 )
 
 func (h oidHasher) writeTypeTag(tag oidTypeTag) {
@@ -3287,6 +3329,13 @@ func (h oidHasher) OperatorOid(name string, leftType, rightType, returnType *tre
 	return h.getOid()
 }
 
+func (h oidHasher) EnumEntryOid(typOID *tree.DOid, physicalRep []byte) *tree.DOid {
+	h.writeTypeTag(enumEntryTypeTag)
+	h.writeOID(typOID)
+	h.writeBytes(physicalRep)
+	return h.getOid()
+}
+
 func tableOid(id sqlbase.ID) *tree.DOid {
 	return tree.NewDOid(tree.DInt(id))
 }