Fallback to kube context if KUBECONFIG is not set (#85)

* Fallback to kube context if KUBECONFIG is not set

Signed-off-by: Jonathan Ogilvie <jonathan.ogilvie@sumologic.com>

* Fallback to kube context if KUBECONFIG is not set

Signed-off-by: Jonathan Ogilvie <jonathan.ogilvie@sumologic.com>

---------

Signed-off-by: Jonathan Ogilvie <jonathan.ogilvie@sumologic.com>

Author: jcogilvie

cmd/diff/diff_test.go

@@ -989,7 +989,9 @@ func TestGetRestConfig(t *testing.T) {
 		"EmptyKubeconfigEnvVar": {
 			kubeconfigPath: "",
 			expectError:    true,
-			errorContains:  "KUBECONFIG environment variable is not set",
+			// With standard loading rules, when KUBECONFIG is empty it tries ~/.kube/config
+			// If that doesn't exist, it returns "invalid configuration"
+			errorContains: "invalid configuration",
 		},
 		"ValidKubeconfigPath": {
 			setupFile: func() string {
@@ -1026,8 +1028,9 @@ users:
 		},
 		"InvalidKubeconfigPath": {
 			kubeconfigPath: "/invalid/nonexistent/path",
-			expectError:    true, // Will error when file doesn't exist
-			errorContains:  "no such file or directory",
+			expectError:    true,
+			// With standard loading rules, invalid path results in "invalid configuration"
+			errorContains: "invalid configuration",
 		},
 	}
 

cmd/diff/main.go

@@ -18,15 +18,13 @@ limitations under the License.
 package main
 
 import (
-	"os"
 	"time"
 
 	"github.com/alecthomas/kong"
 	"k8s.io/client-go/rest"
 	"k8s.io/client-go/tools/clientcmd"
 	"sigs.k8s.io/controller-runtime/pkg/log/zap"
 
-	"github.com/crossplane/crossplane-runtime/v2/pkg/errors"
 	"github.com/crossplane/crossplane-runtime/v2/pkg/logging"
 
 	"github.com/crossplane/crossplane/v2/cmd/crank/version"
@@ -92,10 +90,13 @@ func main() {
 }
 
 func getRestConfig() (*rest.Config, error) {
-	kubeconfig := os.Getenv("KUBECONFIG")
-	if kubeconfig == "" {
-		return nil, errors.New("KUBECONFIG environment variable is not set. Please set KUBECONFIG to point to your kubeconfig file")
-	}
-
-	return clientcmd.BuildConfigFromFlags("", kubeconfig)
+	// Use the standard client-go loading rules:
+	// 1. If KUBECONFIG env var is set, use that
+	// 2. Otherwise, use ~/.kube/config
+	// 3. Respects current context from the kubeconfig
+	loadingRules := clientcmd.NewDefaultClientConfigLoadingRules()
+	configOverrides := &clientcmd.ConfigOverrides{}
+	kubeConfig := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(loadingRules, configOverrides)
+
+	return kubeConfig.ClientConfig()
 }