Use a submodule as safety boundary for BoxedResolver

compiler/rustc_interface/src/passes.rs

@@ -86,21 +86,25 @@ fn count_nodes(krate: &ast::Crate) -> usize {
     counter.count
 }
 
-pub struct BoxedResolver(Pin<Box<BoxedResolverInner>>);
+pub use boxed_resolver::BoxedResolver;
+mod boxed_resolver {
+    use super::*;
 
-// Note: Drop order is important to prevent dangling references. Resolver must be dropped first,
+    pub struct BoxedResolver(Pin<Box<BoxedResolverInner>>);
-// then resolver_arenas and finally session.
+
-// The drop order is defined to be from top to bottom in RFC1857, so there is no need for
+    // Note: Drop order is important to prevent dangling references. Resolver must be dropped first,
-// ManuallyDrop for as long as the fields are not reordered.
+    // then resolver_arenas and finally session.
-struct BoxedResolverInner {
+    // The drop order is defined to be from top to bottom in RFC1857, so there is no need for
+    // ManuallyDrop for as long as the fields are not reordered.
+    struct BoxedResolverInner {
         resolver: Option<Resolver<'static>>,
         resolver_arenas: ResolverArenas<'static>,
         session: Lrc<Session>,
         _pin: PhantomPinned,
-}
+    }
 
-impl BoxedResolver {
+    impl BoxedResolver {
-    fn new<F>(session: Lrc<Session>, make_resolver: F) -> Result<(ast::Crate, Self)>
+        pub(super) fn new<F>(session: Lrc<Session>, make_resolver: F) -> Result<(ast::Crate, Self)>
         where
             F: for<'a> FnOnce(
                 &'a Session,
@@ -148,6 +152,7 @@ impl BoxedResolver {
                 Err(resolver) => resolver.borrow_mut().access(|resolver| resolver.clone_outputs()),
             }
         }
+    }
 }
 
 /// Runs the "early phases" of the compiler: initial `cfg` processing, loading compiler plugins,