client-go: add an Error() function on Request

Requests can accumulate errors with no obvious indication, e.g. if
their primary purpose is to construct a URL: URL() itself doesn't
return an error if r.err is non-nil.

Instead of changing URL() to return an error, which has quite a large
impact, add an Error() function and indicate on URL() that it should
be checked.

Signed-off-by: Stephen Kitt <skitt@redhat.com>

staging/src/k8s.io/client-go/rest/request.go

@@ -481,7 +481,13 @@ func (r *Request) Body(obj interface{}) *Request {
 	return r
 }
 
-// URL returns the current working URL.
+// Error returns any error encountered constructing the request, if any.
+func (r *Request) Error() error {
+	return r.err
+}
+
+// URL returns the current working URL. Check the result of Error() to ensure
+// that the returned URL is valid.
 func (r *Request) URL() *url.URL {
 	p := r.pathPrefix
 	if r.namespaceSet && len(r.namespace) > 0 {

staging/src/k8s.io/client-go/rest/request_test.go

@@ -269,6 +269,26 @@ func TestRequestVersionedParamsFromListOptions(t *testing.T) {
 	}
 }
 
+func TestRequestVersionedParamsWithInvalidScheme(t *testing.T) {
+	parameterCodec := runtime.NewParameterCodec(runtime.NewScheme())
+	r := (&Request{c: &RESTClient{content: ClientContentConfig{GroupVersion: v1.SchemeGroupVersion}}})
+	r.VersionedParams(&v1.PodExecOptions{Stdin: false, Stdout: true},
+		parameterCodec)
+
+	if r.Error() == nil {
+		t.Errorf("should have recorded an error: %#v", r.params)
+	}
+}
+
+func TestRequestError(t *testing.T) {
+	// Invalid body, see TestRequestBody()
+	r := (&Request{}).Body([]string{"test"})
+
+	if r.Error() != r.err {
+		t.Errorf("getter should be identical to reference: %#v %#v", r.Error(), r.err)
+	}
+}
+
 func TestRequestURI(t *testing.T) {
 	r := (&Request{}).Param("foo", "a")
 	r.Prefix("other")