From 72fa8a1a08c7d7572209d19d9849a371faaf9fdf Mon Sep 17 00:00:00 2001
From: Wolfgang Silbermayr <wolfgang@silbermayr.at>
Date: Fri, 5 Aug 2022 12:52:26 +0200
Subject: [PATCH] Seal HostFunctionKind trait

---
 lib/api/src/js/externals/function.rs  | 12 +++++++++++-
 lib/api/src/sys/externals/function.rs | 10 ++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/lib/api/src/js/externals/function.rs b/lib/api/src/js/externals/function.rs
index 3c7bd3017c9..a74a3fa22e0 100644
--- a/lib/api/src/js/externals/function.rs
+++ b/lib/api/src/js/externals/function.rs
@@ -901,7 +901,7 @@ mod inner {
     /// the trait system to automatically generate the appropriate
     /// host functions.
     #[doc(hidden)]
-    pub trait HostFunctionKind {}
+    pub trait HostFunctionKind: private::HostFunctionKindSealed {}
 
     /// An empty struct to help Rust typing to determine
     /// when a `HostFunction` does have an environment.
@@ -915,6 +915,16 @@ mod inner {
 
     impl HostFunctionKind for WithoutEnv {}
 
+    mod private {
+        //! Sealing the HostFunctionKind because it shouldn't be implemented
+        //! by any type outside.
+        //! See:
+        //! https://rust-lang.github.io/api-guidelines/future-proofing.html#c-sealed
+        pub trait HostFunctionKindSealed {}
+        impl HostFunctionKindSealed for super::WithEnv {}
+        impl HostFunctionKindSealed for super::WithoutEnv {}
+    }
+
     /// Represents a low-level Wasm static host function. See
     /// `super::Function::new` and `super::Function::new_env` to learn
     /// more.
diff --git a/lib/api/src/sys/externals/function.rs b/lib/api/src/sys/externals/function.rs
index 1aa1c5f03c9..87bfa8237eb 100644
--- a/lib/api/src/sys/externals/function.rs
+++ b/lib/api/src/sys/externals/function.rs
@@ -1119,6 +1119,16 @@ mod inner {
 
     impl HostFunctionKind for WithoutEnv {}
 
+    mod private {
+        //! Sealing the HostFunctionKind because it shouldn't be implemented
+        //! by any type outside.
+        //! See:
+        //! https://rust-lang.github.io/api-guidelines/future-proofing.html#c-sealed
+        pub trait HostFunctionKindSealed {}
+        impl HostFunctionKindSealed for super::WithEnv {}
+        impl HostFunctionKindSealed for super::WithoutEnv {}
+    }
+
     /// Represents a low-level Wasm static host function. See
     /// [`super::Function::new_typed`] and
     /// [`super::Function::new_typed_with_env`] to learn more.