cli: write Terraform migration output directly to constellation-id.json (#2107)

* backup `constellation-id.json` before upgrade

* remove superfluous `file.Handler` arguments

* merge `constellation-id.json` on upgrade

* fix typo

cli/internal/clusterid/BUILD.bazel

@@ -1,4 +1,5 @@
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("//bazel/go:go_test.bzl", "go_test")
 
 go_library(
     name = "clusterid",
@@ -7,3 +8,10 @@ go_library(
     visibility = ["//cli:__subpackages__"],
     deps = ["//internal/cloud/cloudprovider"],
 )
+
+go_test(
+    name = "clusterid_test",
+    srcs = ["id_test.go"],
+    embed = [":clusterid"],
+    deps = ["@com_github_stretchr_testify//require"],
+)

cli/internal/clusterid/id.go

@@ -28,3 +28,38 @@ type File struct {
 	// It is only set if the cluster is created on Azure.
 	AttestationURL string `json:"attestationURL,omitempty"`
 }
+
+// Merge merges the other file into the current file and returns the result.
+// If a field is set in both files, the value of the other file is used.
+// This does in-place changes on the current file.
+func (f *File) Merge(other File) *File {
+	if other.ClusterID != "" {
+		f.ClusterID = other.ClusterID
+	}
+
+	if other.OwnerID != "" {
+		f.OwnerID = other.OwnerID
+	}
+
+	if other.UID != "" {
+		f.UID = other.UID
+	}
+
+	if other.CloudProvider != cloudprovider.Unknown {
+		f.CloudProvider = other.CloudProvider
+	}
+
+	if other.IP != "" {
+		f.IP = other.IP
+	}
+
+	if other.InitSecret != nil {
+		f.InitSecret = other.InitSecret
+	}
+
+	if other.AttestationURL != "" {
+		f.AttestationURL = other.AttestationURL
+	}
+
+	return f
+}

cli/internal/clusterid/id_test.go

@@ -0,0 +1,63 @@
+/*
+Copyright (c) Edgeless Systems GmbH
+
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+
+package clusterid
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestMerge(t *testing.T) {
+	testCases := map[string]struct {
+		current File
+		other   File
+		want    File
+	}{
+		"empty": {
+			current: File{},
+			other:   File{},
+			want:    File{},
+		},
+		"current empty": {
+			current: File{},
+			other: File{
+				ClusterID: "clusterID",
+			},
+			want: File{
+				ClusterID: "clusterID",
+			},
+		},
+		"other empty": {
+			current: File{
+				ClusterID: "clusterID",
+			},
+			other: File{},
+			want: File{
+				ClusterID: "clusterID",
+			},
+		},
+		"both set": {
+			current: File{
+				ClusterID: "clusterID",
+			},
+			other: File{
+				ClusterID: "otherClusterID",
+			},
+			want: File{
+				ClusterID: "otherClusterID",
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		require := require.New(t)
+
+		ret := tc.current.Merge(tc.other)
+		require.Equal(tc.want, *ret)
+	}
+}