workload/schemachange: correct error code for referencing dropping enum

This patch changes the error code expected for referencing
an enum that's in the process of being dropped to the proper
one. In addition, we ensure that we are returning the proper
error code whenever we get/lookup type descriptors

Epic: none

Release note: None

pkg/sql/catalog/descs/getters.go

@@ -331,7 +331,7 @@ func (g ByNameGetter) Type(
 		tn := tree.MakeTableNameWithSchema(
 			tree.Name(db.GetName()), tree.Name(sc.GetName()), tree.Name(name),
 		)
-		return nil, sqlerrors.NewUndefinedRelationError(&tn)
+		return nil, sqlerrors.NewUndefinedTypeError(&tn)
 	}
 	if tbl, ok := desc.(catalog.TableDescriptor); ok {
 		// A given table name can resolve to either a type descriptor or a table

pkg/sql/resolver.go

@@ -964,8 +964,8 @@ func (l *internalLookupCtx) getTableByID(id descpb.ID) (catalog.TableDescriptor,
 func (l *internalLookupCtx) getTypeByID(id descpb.ID) (catalog.TypeDescriptor, error) {
 	typ, ok := l.typDescs[id]
 	if !ok {
-		return nil, sqlerrors.NewUndefinedRelationError(
-			tree.NewUnqualifiedTableName(tree.Name(fmt.Sprintf("[%d]", id))))
+		return nil, sqlerrors.NewUndefinedTypeError(
+			tree.NewUnqualifiedTypeName(fmt.Sprintf("[%d]", id)))
 	}
 	return typ, nil
 }

pkg/workload/schemachange/operation_generator.go

@@ -4021,7 +4021,7 @@ func (og *operationGenerator) createFunction(ctx context.Context, tx pgx.Tx) (*o
 		// 4. Reference a UDT that does not exist.
 		{pgcode.UndefinedObject, `CREATE FUNCTION { UniqueName } (IN p1 "ThisTypeDoesNotExist") RETURNS VOID LANGUAGE SQL AS $$ SELECT NULL $$`},
 		// 5. Reference an Enum that's in the process of being dropped
-		{pgcode.UndefinedTable, `CREATE FUNCTION { UniqueName } (IN p1 { NonPublicEnum }) RETURNS VOID LANGUAGE SQL AS $$ SELECT NULL $$`},
+		{pgcode.UndefinedObject, `CREATE FUNCTION { UniqueName } (IN p1 { NonPublicEnum }) RETURNS VOID LANGUAGE SQL AS $$ SELECT NULL $$`},
 		// 6. Reference an Enum value that's in the process of being dropped
 		{pgcode.InvalidParameterValue, `CREATE FUNCTION { UniqueName } () RETURNS VOID LANGUAGE SQL AS $$ SELECT { DroppingEnumMember } $$`},
 	}, placeholderMap)