Merge pull request #67707 from apelisse/fix-diff-404

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

diff: Fix crash when remote object doesn't exist

Since we're saving nil in an interface rather than the implementation,
we can't compare to nil to check if the remote object exists or
not. Change the struct to save in the implementation.



**What this PR does / why we need it**:

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```

pkg/kubectl/cmd/diff.go

@@ -265,7 +265,7 @@ type Object interface {
 // InfoObject is an implementation of the Object interface. It gets all
 // the information from the Info object.
 type InfoObject struct {
-	Remote  runtime.Unstructured
+	Remote  *unstructured.Unstructured
 	Info    *resource.Info
 	Encoder runtime.Encoder
 	Parser  *parse.Factory

test/cmd/diff.sh

@@ -26,6 +26,10 @@ run_kubectl_diff_tests() {
     create_and_use_new_namespace
     kube::log::status "Testing kubectl alpha diff"
 
+    # Test that it works when the live object doesn't exist
+    output_message=$(kubectl alpha diff LOCAL LIVE -f hack/testdata/pod.yaml)
+    kube::test::if_has_string "${output_message}" 'test-pod'
+
     kubectl apply -f hack/testdata/pod.yaml
 
     # Ensure that selfLink has been added, and shown in the diff