upgrades: fix desc ID sequence definition to match expectation

pkg/cmd/roachtest/tests/BUILD.bazel

@@ -247,6 +247,7 @@ go_library(
         "@com_github_kr_pretty//:pretty",
         "@com_github_lib_pq//:pq",
         "@com_github_montanaflynn_stats//:stats",
+        "@com_github_pmezard_go_difflib//difflib",
         "@com_github_prometheus_client_golang//api",
         "@com_github_prometheus_client_golang//api/prometheus/v1:prometheus",
         "@com_github_prometheus_common//model",

pkg/cmd/roachtest/tests/validate_system_schema_after_version_upgrade.go

@@ -20,6 +20,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/cmd/roachtest/registry"
 	"github.com/cockroachdb/cockroach/pkg/cmd/roachtest/test"
 	"github.com/cockroachdb/cockroach/pkg/testutils/sqlutils"
+	"github.com/pmezard/go-difflib/difflib"
 )
 
 func registerValidateSystemSchemaAfterVersionUpgrade(r registry.Registry) {
@@ -85,8 +86,18 @@ func registerValidateSystemSchemaAfterVersionUpgrade(r registry.Registry) {
 			validateEquivalenceStep := func(str1, str2 *string) versionStep {
 				return func(ctx context.Context, t test.Test, u *versionUpgradeTest) {
 					if *str1 != *str2 {
-						t.Fatal("After upgrading, `USE system; SHOW CREATE ALL TABLES;` " +
-							"does not match expected output after version upgrade.\n")
+						diff, diffErr := difflib.GetUnifiedDiffString(difflib.UnifiedDiff{
+							A:       difflib.SplitLines(*str1),
+							B:       difflib.SplitLines(*str2),
+							Context: 5,
+						})
+						if diffErr != nil {
+							diff = diffErr.Error()
+							t.Errorf("failed to produce diff: %v", diffErr)
+						}
+						t.Fatalf("After upgrading, `USE system; SHOW CREATE ALL TABLES;` "+
+							"does not match expected output after version upgrade."+
+							"\nDiff:\n%s", diff)
 					}
 					t.L().Printf("validating succeeded:\n%v", *str1)
 				}

pkg/upgrade/upgrades/desc_id_sequence_for_system_tenant.go

@@ -17,7 +17,6 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/kv"
 	"github.com/cockroachdb/cockroach/pkg/sql/catalog/systemschema"
-	"github.com/cockroachdb/cockroach/pkg/sql/catalog/tabledesc"
 	"github.com/cockroachdb/cockroach/pkg/upgrade"
 )
 
@@ -27,14 +26,19 @@ func descIDSequenceForSystemTenant(
 	if !d.Codec.ForSystemTenant() {
 		return nil
 	}
-	mut := tabledesc.NewBuilder(systemschema.DescIDSequence.TableDesc()).BuildCreatedMutableTable()
 	return d.DB.Txn(ctx, func(ctx context.Context, txn *kv.Txn) error {
 		oldEntry, err := txn.GetForUpdate(ctx, keys.LegacyDescIDGenerator)
 		if err != nil {
 			return err
 		}
-		mut.SequenceOpts.Start = oldEntry.ValueInt()
-		_, _, err = CreateSystemTableInTxn(ctx, d.Settings, txn, keys.SystemSQLCodec, mut)
-		return err
+		id, created, err := CreateSystemTableInTxn(
+			ctx, d.Settings, txn, keys.SystemSQLCodec, systemschema.DescIDSequence,
+		)
+		if err != nil || !created {
+			return err
+		}
+		// Install the appropriate value for the sequence. Note that we use the
+		// existence of the sequence above to make this transaction idempotent.
+		return txn.Put(ctx, d.Codec.SequenceKey(uint32(id)), oldEntry.ValueInt())
 	})
 }