analyze: fix comments

c2rust-analyze/src/borrowck/type_check.rs

@@ -603,7 +603,9 @@ impl<'tcx> TypeChecker<'tcx, '_> {
                         });
                     }
                     Callee::Null { .. } => {
-                        // TODO: do we need to do anything here?
+                        // Just visit the place.  The null pointer returned here has no origin, so
+                        // there's no need to call `do_assign` to set up subset relations.
+                        let _pl_lty = self.visit_place(destination);
                     }
                 }
             }

c2rust-analyze/src/util.rs

@@ -346,7 +346,7 @@ fn builtin_callee<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, substs: SubstsRef<'tcx>)
         }
 
         "null" | "null_mut" => {
-            // The `core::mem::size_of` function.
+            // The `core::ptr::null/null_mut` function.
             let parent_did = tcx.parent(did);
             if tcx.def_kind(parent_did) != DefKind::Mod {
                 return None;