[dnm] clusterversion,heartbeat: remove hack to bump versions willy nilly

This reverts an earlier commit removing version upgrade safeguards. This
commit will also not be merged.

Release note: None

pkg/clusterversion/setting.go

@@ -225,6 +225,11 @@ func (cv *clusterVersionSetting) validateBinaryVersions(
 	if vh.BinaryMinSupportedVersion() == (roachpb.Version{}) {
 		panic("BinaryMinSupportedVersion not set")
 	}
+	if vh.BinaryVersion().Less(ver) {
+		// TODO(tschottdorf): also ask gossip about other nodes.
+		return errors.Errorf("cannot upgrade to %s: node running %s",
+			ver, vh.BinaryVersion())
+	}
 	if ver.Less(vh.BinaryMinSupportedVersion()) {
 		return errors.Errorf("node at %s cannot run %s (minimum version is %s)",
 			vh.BinaryVersion(), ver, vh.BinaryMinSupportedVersion())

pkg/kv/kvserver/stores.go

@@ -340,6 +340,14 @@ func SynthesizeClusterVersionFromEngines(
 			cv.Version = binaryMinSupportedVersion
 		}
 
+		// Avoid running a binary with a store that is too new. For example,
+		// restarting into 1.1 after having upgraded to 1.2 doesn't work.
+		if binaryVersion.Less(cv.Version) {
+			return clusterversion.ClusterVersion{}, errors.Errorf(
+				"cockroach version v%s is incompatible with data in store %s; use version v%s or later",
+				binaryVersion, eng, cv.Version)
+		}
+
 		// Track smallest use version encountered.
 		if cv.Version.Less(minStoreVersion.Version) {
 			minStoreVersion.Version = cv.Version

pkg/rpc/heartbeat.go

@@ -90,6 +90,10 @@ func checkVersion(ctx context.Context, st *cluster.Settings, peerVersion roachpb
 		return errors.Errorf(
 			"cluster requires at least version %s, but peer did not provide a version", activeVersion)
 	}
+	if peerVersion.Less(activeVersion.Version) {
+		return errors.Errorf(
+			"cluster requires at least version %s, but peer has version %s", activeVersion, peerVersion)
+	}
 	return nil
 }