Work around new dead_code warnings

    warning: field `0` is never read
      --> macro/src/syntax/mod.rs:52:13
       |
    52 |     Include(Include),
       |     ------- ^^^^^^^
       |     |
       |     field in this variant
       |
       = note: `#[warn(dead_code)]` on by default
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
       |
    52 |     Include(()),
       |             ~~

    warning: fields `0` and `1` are never read
     --> macro/src/syntax/cfg.rs:9:8
      |
    9 |     Eq(Ident, Option<LitStr>),
      |     -- ^^^^^  ^^^^^^^^^^^^^^
      |     |
      |     fields in this variant
      |
    help: consider changing the fields to be of unit type to suppress this warning while preserving the field numbering, or remove the fields
      |
    9 |     Eq((), ()),
      |        ~~  ~~

    warning: field `0` is never read
      --> macro/src/syntax/cfg.rs:11:9
       |
    11 |     Any(Vec<CfgExpr>),
       |     --- ^^^^^^^^^^^^
       |     |
       |     field in this variant
       |
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
       |
    11 |     Any(()),
       |         ~~

    warning: field `0` is never read
      --> macro/src/syntax/cfg.rs:12:9
       |
    12 |     Not(Box<CfgExpr>),
       |     --- ^^^^^^^^^^^^
       |     |
       |     field in this variant
       |
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
       |
    12 |     Not(()),
       |         ~~

    warning: field `0` is never read
       --> src/lib.rs:551:13
        |
    551 | struct void(core::ffi::c_void);
        |        ---- ^^^^^^^^^^^^^^^^^
        |        |
        |        field in this struct
        |
        = note: `#[warn(dead_code)]` on by default
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
        |
    551 | struct void(());
        |             ~~

    warning: field `0` is never read
       --> tests/ffi/lib.rs:411:26
        |
    411 | pub struct Reference<'a>(&'a String);
        |            ---------     ^^^^^^^^^^
        |            |
        |            field in this struct
        |
        = note: `#[warn(dead_code)]` on by default
    help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
        |
    411 | pub struct Reference<'a>(());
        |                          ~~

src/lib.rs

@@ -548,4 +548,4 @@ chars! {
 }
 
 #[repr(transparent)]
-struct void(core::ffi::c_void);
+struct void(#[allow(dead_code)] core::ffi::c_void);

syntax/cfg.rs

@@ -6,9 +6,12 @@ use syn::{parenthesized, token, Attribute, LitStr, Token};
 #[derive(Clone)]
 pub(crate) enum CfgExpr {
     Unconditional,
+    #[allow(dead_code)] // only used by cxx-build, not cxxbridge-macro
     Eq(Ident, Option<LitStr>),
     All(Vec<CfgExpr>),
+    #[allow(dead_code)] // only used by cxx-build, not cxxbridge-macro
     Any(Vec<CfgExpr>),
+    #[allow(dead_code)] // only used by cxx-build, not cxxbridge-macro
     Not(Box<CfgExpr>),
 }
 

syntax/mod.rs

@@ -49,6 +49,7 @@ pub(crate) use self::parse::parse_items;
 pub(crate) use self::types::Types;
 
 pub(crate) enum Api {
+    #[allow(dead_code)] // only used by cxx-build, not cxxbridge-macro
     Include(Include),
     Struct(Struct),
     Enum(Enum),

tests/ffi/lib.rs

@@ -408,7 +408,7 @@ impl R {
     }
 }
 
-pub struct Reference<'a>(&'a String);
+pub struct Reference<'a>(pub &'a String);
 
 impl ffi::Shared {
     fn r_method_on_shared(&self) -> String {