Update troubles

TROUBLES.md

@@ -6,7 +6,7 @@
   passing an array of small elements (small structs or integers). Building such an array with a `Vec` can be expensive, especially
   when most of the time the array only contains a single element.
 
-- No way to create a `*mut T` pointer from a `*mut c_void()` and a size when `T` is unsized. This had to be implemented in a custom
+- No way to create a `*mut T` pointer from a `*mut c_void` and a size when `T` is unsized. This had to be implemented in a custom
   trait.
 
 - [Can't cast an `ImageResource` into a `Resource` even though the former depends on the latter](https://github.com/rust-lang/rust/issues/5665).
@@ -17,4 +17,8 @@
 - https://github.com/rust-lang/rust/issues/29328
 
 - Some trait implementations have an associated type that looks like `type T = (Arc<Foo>, Arc<Bar>);`. HKTs would allow this parameter to take
-  references to the Arcs instead, and avoid having to clone them.
+  references to the Arcs instead, and avoid having to clone them. This problem could by bypassed by making the code more ugly, but it's not worth
+  it just to avoid cloning some Arcs.
+
+- Visibility rules mean that you can't write `struct Error; pub mod foo { pub struct Foo; impl From<Error> for Foo { ... } }`. Rustc complains
+  that `Error` is private an exported in `Foo`'s signature, even though that's in the author's opinion a totally legitimate usage.