add diff suppress for empty network policy in container cluster

google/resource_container_cluster.go

@@ -310,6 +310,7 @@ func resourceContainerCluster() *schema.Resource {
 						},
 					},
 				},
+				DiffSuppressFunc: emptyOrDefaultStringSuppress("PROVIDER_UNSPECIFIED"),
 			},
 
 			"node_config": schemaNodeConfig,

google/utils.go

@@ -184,6 +184,12 @@ func optionalPrefixSuppress(prefix string) schema.SchemaDiffSuppressFunc {
 	}
 }
 
+func emptyOrDefaultStringSuppress(defaultVal string) schema.SchemaDiffSuppressFunc {
+	return func(k, old, new string, d *schema.ResourceData) bool {
+		return (old == "" && new == defaultVal) || (new == "" && old == defaultVal)
+	}
+}
+
 func ipCidrRangeDiffSuppress(k, old, new string, d *schema.ResourceData) bool {
 	// The range may be a:
 	// A) single IP address (e.g. 10.2.3.4)

google/utils_test.go

@@ -404,3 +404,43 @@ func TestDatasourceSchemaFromResourceSchema(t *testing.T) {
 		})
 	}
 }
+
+func TestEmptyOrDefaultStringSuppress(t *testing.T) {
+	testFunc := emptyOrDefaultStringSuppress("default value")
+
+	cases := map[string]struct {
+		Old, New          string
+		ExpectDiffSupress bool
+	}{
+		"same value, format changed from empty to default": {
+			Old:               "",
+			New:               "default value",
+			ExpectDiffSupress: true,
+		},
+		"same value, format changed from default to empty": {
+			Old:               "default value",
+			New:               "",
+			ExpectDiffSupress: true,
+		},
+		"different value, format changed from empty to non-default": {
+			Old:               "",
+			New:               "not default new",
+			ExpectDiffSupress: false,
+		},
+		"different value, format changed from non-default to empty": {
+			Old:               "not default old",
+			New:               "",
+			ExpectDiffSupress: false,
+		},
+		"different value, format changed from non-default to non-default": {
+			Old:               "not default 1",
+			New:               "not default 2",
+			ExpectDiffSupress: false,
+		},
+	}
+	for tn, tc := range cases {
+		if testFunc("", tc.Old, tc.New, nil) != tc.ExpectDiffSupress {
+			t.Errorf("bad: %s, '%s' => '%s' expect DiffSuppress to return %t", tn, tc.Old, tc.New, tc.ExpectDiffSupress)
+		}
+	}
+}