PointerSlot uses &'static

youknowone · youknowone · commit 3884481eafbe · 2022-07-23T16:41:39.000+09:00
diff --git a/vm/src/builtins/type.rs b/vm/src/builtins/type.rs
@@ -20,7 +20,7 @@ use crate::{
 };
 use indexmap::{map::Entry, IndexMap};
 use itertools::Itertools;
-use std::{borrow::Borrow, collections::HashSet, fmt, ops::Deref, pin::Pin, ptr::NonNull};
+use std::{borrow::Borrow, collections::HashSet, fmt, ops::Deref, pin::Pin};
 
 /// type(object_or_name, bases, dict)
 /// type(object) -> the object's type
@@ -41,7 +41,7 @@ pub struct HeapTypeExt {
     pub number_methods: PyNumberMethods,
 }
 
-pub struct PointerSlot<T>(NonNull<T>);
+pub struct PointerSlot<T: 'static>(&'static T);
 
 impl<T> Clone for PointerSlot<T> {
     fn clone(&self) -> Self {
@@ -53,24 +53,28 @@ impl<T> Copy for PointerSlot<T> {}
 
 impl<T> From<&'static T> for PointerSlot<T> {
     fn from(x: &'static T) -> Self {
-        Self(NonNull::from(x))
+        Self(x)
     }
 }
 
 impl<T> AsRef<T> for PointerSlot<T> {
-    fn as_ref(&self) -> &T {
-        unsafe { self.0.as_ref() }
+    fn as_ref(&self) -> &'static T {
+        self.0
     }
 }
 
 impl<T> PointerSlot<T> {
+    /// # Safety
+    /// typ must live long enough
     pub unsafe fn from_heaptype<F>(typ: &PyType, f: F) -> Option<Self>
     where
-        F: FnOnce(&HeapTypeExt) -> &T,
+        F: FnOnce(&'static HeapTypeExt) -> &'static T,
     {
-        typ.heaptype_ext
-            .as_ref()
-            .map(|ext| Self(NonNull::from(f(ext))))
+        typ.heaptype_ext.as_ref().map(|ext| {
+            let ext: &HeapTypeExt = &ext.as_ref();
+            let ext: &'static _ = &*(ext as *const _); // lease lifetime by trusting `typ` live long enough
+            Self(f(ext))
+        })
     }
 }
 
