From d27bcbf19eae8cabf1ee9b3ad0243e3fa5bb6975 Mon Sep 17 00:00:00 2001
From: Lofty <dan.ravensloft@gmail.com>
Date: Wed, 23 Nov 2022 03:47:04 +0000
Subject: [PATCH] awooter: fix an API soundness issue

---
 common/route/awooter/rust/src/npnr.rs | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/common/route/awooter/rust/src/npnr.rs b/common/route/awooter/rust/src/npnr.rs
index 90bd7fd0..1ceab4c4 100644
--- a/common/route/awooter/rust/src/npnr.rs
+++ b/common/route/awooter/rust/src/npnr.rs
@@ -54,7 +54,14 @@ pub struct PortRef {
 }
 
 impl PortRef {
-    pub fn cell(&self) -> Option<&mut CellInfo> {
+    pub fn cell(&self) -> Option<&CellInfo> {
+        // SAFETY: handing out &s is safe when we have &self.
+        unsafe { npnr_portref_cell(self).as_ref() }
+    }
+
+    pub fn cell_mut(&mut self) -> Option<&mut CellInfo> {
+        // SAFETY: handing out &mut is safe when we have &mut self
+        // as getting multiple &mut CellInfo would require multiple &mut PortRef.
         unsafe { npnr_portref_cell(self).as_mut() }
     }
 }