example broken logic

Summary:
~~This implementation is broken. The test unintentionally uses the "all fields optional" branch. By adding another field to the struct that isn't optional, the "deprecated_optional_with_default_is_some" option doesn't work as expected.~~

~~I originally thought the test was only passing due to a [special conditional branch in our thrift derserialization that applies when all the fields of a struct are optional](https://www.internalfb.com/code/fbsource/[026629593ef48013189d2a74e0cb9af0baa29e86]/xplat/thrift/compiler/generate/templates/rust/lib/structimpl.mustache?lines=153-159). Now, I think the test is just wrong. I think the test struct should be instantiated with "IAMOPTWITHDEF" as the value. Then test to ensure any null or missing values get derserialized to "IAMOPTWITHDEF"~~

Back to the original idea, this test needs to be updated.

Reviewed By: diliop

Differential Revision: D76012935

fbshipit-source-id: 9872f9a4391006d07aeca387891ecb8e550f6dee

Author: cjlongoria

third-party/thrift/src/thrift/lib/rust/src/dep_tests/simplejson.rs

@@ -312,10 +312,14 @@ fn test_deprecated_null_stuff_deser() -> Result<()> {
 
     let sub = test_deprecated_optional_with_default_is_some_if::Struct {
         optDef: None,
+        marker: true,
         ..Default::default()
     };
 
-    let inputs = &["{}", r#"{ "optDef": null}"#];
+    let inputs = &[
+        r#"{                 "marker": true }"#,
+        r#"{ "optDef": null, "marker": true }"#,
+    ];
     for input in inputs {
         // Make sure everything is skipped properly
         let res = deserialize(*input);

third-party/thrift/src/thrift/lib/rust/src/dep_tests/test_deprecated_optional_with_default_is_some.thrift

@@ -19,6 +19,7 @@ namespace cpp2 facebook
 struct Struct {
   // @lint-ignore THRIFTCHECKS
   1: optional string optDef = "IAMOPTWITHDEF";
+  2: bool marker;
 }
 
 const Struct DEFAULT_STRUCT = {};