kubernetes/migration: dont error out on no-op same-verison upgrades (#171)

* dont error out on no-op same-verison upgrades

* test case fixes

kubernetes/migration/migrate.go

@@ -26,15 +26,18 @@ func Unsupported(fromCoreDNSVersion, toCoreDNSVersion, corefileStr string) ([]No
 }
 
 func getStatus(fromCoreDNSVersion, toCoreDNSVersion, corefileStr, status string) ([]Notice, error) {
-	notices := []Notice{}
+	if fromCoreDNSVersion == toCoreDNSVersion {
+		return nil, nil
+	}
 	err := validateVersions(fromCoreDNSVersion, toCoreDNSVersion)
 	if err != nil {
-		return notices, err
+		return nil, err
 	}
 	cf, err := corefile.New(corefileStr)
 	if err != nil {
-		return notices, err
+		return nil, err
 	}
+	notices := []Notice{}
 	v := fromCoreDNSVersion
 	for {
 		v = Versions[v].nextVersion
@@ -126,6 +129,9 @@ func getStatus(fromCoreDNSVersion, toCoreDNSVersion, corefileStr, status string)
 // If deprecations is true, deprecated plugins/options will be migrated as soon as they are deprecated.
 // If deprecations is false, deprecated plugins/options will be migrated only once they become removed or ignored.
 func Migrate(fromCoreDNSVersion, toCoreDNSVersion, corefileStr string, deprecations bool) (string, error) {
+	if fromCoreDNSVersion == toCoreDNSVersion {
+		return corefileStr, nil
+	}
 	err := validateVersions(fromCoreDNSVersion, toCoreDNSVersion)
 	if err != nil {
 		return "", err

kubernetes/migration/migrate_test.go

@@ -184,6 +184,44 @@ mystub-2.example.org {
     errors
     cache 30
 }
+`,
+		},
+		{
+			name:         "no-op same version migration",
+			fromVersion:  "1.3.1",
+			toVersion:    "1.3.1",
+			deprecations: true,
+			startCorefile: `.:53 {
+    errors
+    health
+    kubernetes cluster.local in-addr.arpa ip6.arpa {
+        pods insecure
+        upstream
+        fallthrough in-addr.arpa ip6.arpa
+    }
+    prometheus :9153
+    proxy . /etc/resolv.conf
+    cache 30
+    loop
+    reload
+    loadbalance
+}
+`,
+			expectedCorefile: `.:53 {
+    errors
+    health
+    kubernetes cluster.local in-addr.arpa ip6.arpa {
+        pods insecure
+        upstream
+        fallthrough in-addr.arpa ip6.arpa
+    }
+    prometheus :9153
+    proxy . /etc/resolv.conf
+    cache 30
+    loop
+    reload
+    loadbalance
+}
 `,
 		},
 	}
@@ -245,6 +283,15 @@ func TestDeprecated(t *testing.T) {
 			t.Errorf("expected to get '%v'; got '%v'", dep.ToString(), result[i].ToString())
 		}
 	}
+
+	result, err = Deprecated("1.3.1", "1.3.1", startCorefile)
+	if err != nil {
+		t.Fatal(err)
+	}
+	expected = []Notice{}
+	if len(result) != len(expected) {
+		t.Fatalf("expected to find %v notifications in no-op upgrade; got %v", len(expected), len(result))
+	}
 }
 
 func TestUnsupported(t *testing.T) {
@@ -377,6 +424,7 @@ func TestValidateVersions(t *testing.T) {
 		to        string
 		shouldErr bool
 	}{
+		{"1.3.1", "1.3.1", true},
 		{"1.3.1", "1.5.0", false},
 		{"1.5.0", "1.3.1", true},
 		{"banana", "1.5.0", true},