rust : use repr(transparent) when we should

Change-Id: Iaf8334aa8d83c170454dffc8438395a395246938
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/198557
Reviewed-by: Arnaud Versini <arnaud.versini@pm.me>
Tested-by: Jenkins

codemaker/source/rustmaker/rustproduce.cxx

@@ -613,6 +613,7 @@ void RustProducer::generateInterfaceWrapper(
         .endLine()
         .beginLine()
         .append("#[allow(non_camel_case_types)]")
+        .append("#[repr(transparent)]")
         .endLine()
         .beginLine()
         .append("pub struct ")

rust_uno/src/core/any.rs

@@ -34,6 +34,7 @@ use crate::ffi::uno_any::*;
 ///
 /// Any provides a safe, memory-managed interface to LibreOffice's native
 /// any type. It automatically handles reference counting and memory cleanup.
+#[repr(transparent)]
 pub struct Any {
     inner: uno_Any,
 }

rust_uno/src/core/oustring.rs

@@ -36,6 +36,7 @@ use crate::ffi::sal_types::*;
 /// OUString provides a safe, memory-managed interface to LibreOffice's native
 /// string type. It automatically handles reference counting and memory cleanup,
 /// and provides conversions to/from standard Rust string types.
+#[repr(transparent)]
 pub struct OUString {
     inner: NonNull<rtl_uString>,
 }

rust_uno/src/core/sequence.rs

@@ -37,6 +37,7 @@ use std::ptr::NonNull;
 ///
 /// Sequence provides a safe, memory-managed interface to LibreOffice's native
 /// Sequence type. It automatically handles reference counting and memory cleanup.
+#[repr(transparent)]
 pub struct Sequence {
     inner: NonNull<uno_Sequence>,
 }

rust_uno/src/core/type.rs

@@ -54,6 +54,7 @@ use std::ptr;
 /// ));
 /// ```
 #[allow(non_snake_case)] // _pType follows FFI naming conventions
+#[repr(transparent)]
 pub struct Type {
     /// C typelib reference pointer
     _pType: *mut typelib_TypeDescriptionReference,