From 8aa08225cd5575bb6a590bdf11dcfd0ceb772203 Mon Sep 17 00:00:00 2001
From: Ivan Enderlin <ivan@mnt.io>
Date: Thu, 17 Dec 2020 14:55:29 +0100
Subject: [PATCH] feat(c-api) `wasm_$name_vec_delete` checks the vec is
 initialized.

In case of a boxed vector, `wasm_$name_vec_delete` now checks that the
vec is correctly initialized (by checking the first item only) because
transmuting `Vec<*mut T>` to `Vec<Box<T>>`, otherwise it will crash.
---
 lib/c-api/src/wasm_c_api/macros.rs | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/c-api/src/wasm_c_api/macros.rs b/lib/c-api/src/wasm_c_api/macros.rs
index 07a99b01545..8132f5cc5c2 100644
--- a/lib/c-api/src/wasm_c_api/macros.rs
+++ b/lib/c-api/src/wasm_c_api/macros.rs
@@ -274,7 +274,14 @@ Read the documentation of [`wasm_" $name "_t`] to see more concrete examples."]
                 let vec = &mut *ptr;
                 if !vec.data.is_null() {
                     let data: Vec<*mut [<wasm_ $name _t>]> = Vec::from_raw_parts(vec.data, vec.size, vec.size);
-                    let _data: Vec<Box<[<wasm_ $name _t>]>> = ::std::mem::transmute(data);
+
+                    // If the vector has been initialized (we check
+                    // only the first item), we can transmute items to
+                    // `Box`es.
+                    if vec.size > 0 && !data[0].is_null() {
+                        let _data: Vec<Box<[<wasm_ $name _t>]>> = ::std::mem::transmute(data);
+                    }
+
                     vec.data = ::std::ptr::null_mut();
                     vec.size = 0;
                 }
@@ -299,7 +306,6 @@ macro_rules! wasm_declare_ref_base {
             }
 
             // TODO: finish this...
-
         }
     };
 }