Suppress dead_code on fields only accessed by deserialize_in_place

error: field `option` is never read
       --> test_suite/tests/test_gen.rs:666:9
        |
    665 |     struct ImplicitlyBorrowedOption<'a> {
        |            ------------------------ field in this struct
    666 |         option: std::option::Option<&'a str>,
        |         ^^^^^^
        |
    note: the lint level is defined here
       --> test_suite/tests/test_gen.rs:5:9
        |
    5   | #![deny(warnings)]
        |         ^^^^^^^^
        = note: `#[deny(dead_code)]` implied by `#[deny(warnings)]`

    error: fields `ty` and `id` are never read
       --> test_suite/tests/test_gen.rs:696:9
        |
    695 |     struct RelObject<'a> {
        |            --------- fields in this struct
    696 |         ty: &'a str,
        |         ^^
    697 |         id: String,
        |         ^^

    error: field `field` is never read
       --> test_suite/tests/test_gen.rs:740:17
        |
    739 |             struct MacroRules<'a> {
        |                    ---------- field in this struct
    740 |                 field: $field,
        |                 ^^^^^
    ...
    745 |     deriving!(&'a str);
        |     ------------------ in this macro invocation
        |
        = note: this error originates in the macro `deriving` (in Nightly builds, run with -Z macro-backtrace for more info)

    error: field `f` is never read
       --> test_suite/tests/test_gen.rs:756:9
        |
    754 |     struct BorrowLifetimeInsideMacro<'a> {
        |            ------------------------- field in this struct
    755 |         #[serde(borrow = "'a")]
    756 |         f: mac!(Cow<'a, str>),
        |         ^

    warning: fields `question` and `answer` are never read
        --> test_suite/tests/test_annotations.rs:2969:9
         |
    2968 |     struct Struct {
         |            ------ fields in this struct
    2969 |         question: String,
         |         ^^^^^^^^
    2970 |         answer: u32,
         |         ^^^^^^
         |
         = note: `#[warn(dead_code)]` on by default

test_suite/tests/test_annotations.rs

@@ -2966,7 +2966,9 @@ fn test_expecting_message() {
     #[derive(Deserialize)]
     #[serde(expecting = "something strange...")]
     struct Struct {
+        #[allow(dead_code)]
         question: String,
+        #[allow(dead_code)]
         answer: u32,
     }