From 06710fce596371b2130c6e7aebe2472dd935b4ab Mon Sep 17 00:00:00 2001
From: Cassie Jones <code@witchoflight.com>
Date: Sat, 2 Jan 2021 17:37:58 -0500
Subject: [PATCH] [rt] Change destructor decref to use immutable slices

It should be safe since the destructor should have exclusive access to
the object, but this avoids making potentially aliased references.
---
 rt/src/lam.rs | 20 ++++++++++++++++----
 rt/src/lib.rs |  4 ++--
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/rt/src/lam.rs b/rt/src/lam.rs
index b998fa8..ffdb5f6 100644
--- a/rt/src/lam.rs
+++ b/rt/src/lam.rs
@@ -98,17 +98,29 @@ impl ObjLam {
         ObjLam::size_of(self.params, self.upvars)
     }
 
-    pub(crate) unsafe fn raw_fields_mut(&mut self) -> *mut Obj {
-        (self as *mut ObjLam).add(1) as *mut Obj
+    fn raw_fields_mut(&self) -> *mut Obj {
+        unsafe { (self as *const ObjLam).add(1) as *mut Obj }
     }
 
-    pub(crate) unsafe fn params_mut(&mut self) -> &mut [Obj] {
+    unsafe fn params_mut(&mut self) -> &mut [Obj] {
         let ptr = self.raw_fields_mut();
         core::slice::from_raw_parts_mut(ptr, self.params as usize)
     }
 
-    pub(crate) unsafe fn upvars_mut(&mut self) -> &mut [Obj] {
+    pub(crate) fn params(&self) -> &[Obj] {
+        let ptr = self.raw_fields_mut();
+        unsafe { core::slice::from_raw_parts(ptr, self.params as usize) }
+    }
+
+    unsafe fn upvars_mut(&mut self) -> &mut [Obj] {
         let ptr = self.raw_fields_mut().add(self.params as usize);
         core::slice::from_raw_parts_mut(ptr, self.upvars as usize)
     }
+
+    pub(crate) fn upvars(&self) -> &[Obj] {
+        unsafe {
+            let ptr = self.raw_fields_mut().add(self.params as usize);
+            core::slice::from_raw_parts(ptr, self.upvars as usize)
+        }
+    }
 }
diff --git a/rt/src/lib.rs b/rt/src/lib.rs
index 626a65d..2bd2386 100644
--- a/rt/src/lib.rs
+++ b/rt/src/lib.rs
@@ -143,10 +143,10 @@ impl Obj {
         }
         if self.is_lam() {
             let lam = &mut *self.box_lam;
-            for param in lam.params_mut() {
+            for param in lam.params() {
                 param.decref();
             }
-            for upvar in lam.upvars_mut() {
+            for upvar in lam.upvars() {
                 upvar.decref();
             }
         }
-- 
2.47.0