assert that dynamized traits are object-safe

3 files changed, 30 insertions, 1 deletions

diff --git a/README.md b/README.md
index e6c715e..77d28d1 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ let object = &client as &dyn Client;
 
 The last line of the above code fails to compile with:
 
-> error[E0191]: the value of the associated type `Error` (from trait `Client`)
+> error\[E0191\]: the value of the associated type `Error` (from trait `Client`)
 > must be specified
 
 Sometimes you however want a trait object to be able to encompass trait
diff --git a/src/lib.rs b/src/lib.rs
index a190cb9..85718d0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -308,12 +308,18 @@ pub fn dynamize(_attr: TokenStream, input: TokenStream) -> TokenStream {
 
     let blanket_impl = generate_blanket_impl(&dyn_trait, &original_trait, &method_impls);
 
+    let dyn_trait_name = &dyn_trait.ident;
+    let (impl_generics, ty_generics, where_clause) = dyn_trait.generics.split_for_impl();
+
     let expanded = quote! {
         #original_trait
 
         #(#dyn_trait_attrs)*
         #dyn_trait
 
+        // assert that dyn_trait can actually be made into an object
+        impl #impl_generics dyn #dyn_trait_name #ty_generics #where_clause {}
+
         #(#blanket_impl_attrs)*
         #blanket_impl
     };
@@ -432,3 +438,7 @@ fn path_segment_for_trait(sometrait: &ItemTrait) -> PathSegment {
         },
     }
 }
+
+#[doc = include_str!("../tests/doctests.md")]
+#[cfg(doctest)]
+struct Doctests;
diff --git a/tests/doctests.md b/tests/doctests.md
new file mode 100644
index 0000000..ef557fe
--- /dev/null
+++ b/tests/doctests.md
@@ -0,0 +1,19 @@
+Tests that the object-safety assertion via `impl dyn` is working:
+
+```rust compile_fail
+trait ObjectUnsafe: Sized {}
+
+#[dynamize::dynamize]
+trait Trait: ObjectUnsafe {}
+```
+
+```rust compile_fail
+trait ObjectUnsafe: Sized {}
+
+#[dynamize::dynamize]
+trait Trait {
+    type A: ObjectUnsafe;
+
+    fn f(&self) -> Self::A;
+}
+```