CFI: Fix fn items, closures, and Fn trait objects

Fix casting between function items, closures, and Fn trait objects by
transforming function items, closures, and Fn trait objects into
function pointers for encoding.

compiler/rustc_middle/src/ty/context.rs

@@ -1841,7 +1841,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// does not compute the full elaborated super-predicates but just the set of def-ids. It is used
     /// to identify which traits may define a given associated type to help avoid cycle errors.
     /// Returns a `DefId` iterator.
-    fn super_traits_of(self, trait_def_id: DefId) -> impl Iterator<Item = DefId> + 'tcx {
+    pub fn super_traits_of(self, trait_def_id: DefId) -> impl Iterator<Item = DefId> + 'tcx {
         let mut set = FxHashSet::default();
         let mut stack = vec![trait_def_id];
 

compiler/rustc_middle/src/ty/sty.rs

@@ -1836,6 +1836,11 @@ impl<'tcx> Ty<'tcx> {
         self.0.0.flags
     }
 
+    #[inline]
+    pub fn is_tuple(self) -> bool {
+        matches!(self.kind(), Tuple(..))
+    }
+
     #[inline]
     pub fn is_unit(self) -> bool {
         match self.kind() {
@@ -2208,6 +2213,11 @@ impl<'tcx> Ty<'tcx> {
         matches!(self.kind(), FnDef(..) | FnPtr(_))
     }
 
+    #[inline]
+    pub fn is_fn_def(self) -> bool {
+        matches!(self.kind(), FnDef(..))
+    }
+
     #[inline]
     pub fn is_fn_ptr(self) -> bool {
         matches!(self.kind(), FnPtr(_))

compiler/rustc_symbol_mangling/src/lib.rs

@@ -92,6 +92,7 @@
 #![feature(rustdoc_internals)]
 #![feature(let_chains)]
 #![allow(internal_features)]
+#![feature(iter_order_by)]
 
 #[macro_use]
 extern crate rustc_middle;