Merge pull request #36 from dtolnay/currentcrate

Enforce ref_cast_custom used from same crate as corresponding RefCastCustom

Cargo.toml

@@ -14,11 +14,12 @@ rust-version = "1.31"
 ref-cast-impl = { version = "=1.0.11", path = "derive" }
 
 [dev-dependencies]
+ref-cast-test-suite = { version = "0", path = "tests/helper" }
 rustversion = "1.0"
 trybuild = { version = "1.0.52", features = ["diff"] }
 
 [workspace]
-members = ["derive"]
+members = ["derive", "tests/helper"]
 
 [package.metadata.docs.rs]
 targets = ["x86_64-unknown-linux-gnu"]

derive/src/lib.rs

@@ -279,6 +279,7 @@ fn expand_ref_cast(input: DeriveInput) -> Result<TokenStream2> {
 fn expand_ref_cast_custom(input: DeriveInput) -> Result<TokenStream2> {
     check_repr(&input)?;
 
+    let vis = &input.vis;
     let name = &input.ident;
     let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
 
@@ -301,9 +302,15 @@ fn expand_ref_cast_custom(input: DeriveInput) -> Result<TokenStream2> {
     };
 
     Ok(quote! {
-        unsafe impl #impl_generics ::ref_cast::__private::RefCastCustom<#from> for #name #ty_generics #where_clause {
-            #assert_trivial_fields
-        }
+        const _: () = {
+            #[non_exhaustive]
+            #vis struct RefCastCurrentCrate {}
+
+            unsafe impl #impl_generics ::ref_cast::__private::RefCastCustom<#from> for #name #ty_generics #where_clause {
+                type CurrentCrate = RefCastCurrentCrate;
+                #assert_trivial_fields
+            }
+        };
     })
 }
 
@@ -335,9 +342,14 @@ fn expand_function_body(function: Function) -> TokenStream2 {
         #(#attrs)*
         #vis #constness #asyncness #unsafety #abi
         #fn_token #ident #generics #args #arrow_token #to_type {
+            // check lifetime
             let _ = || {
                 ::ref_cast::__private::ref_cast_custom::<#from_type, #to_type>(#arg);
             };
+
+            // check same crate
+            let _ = ::ref_cast::__private::CurrentCrate::<#from_type, #to_type> {};
+
             unsafe {
                 ::ref_cast::__private::transmute::<#from_type, #to_type>(#arg)
             }

src/custom.rs

@@ -1,25 +1,51 @@
 // Not public API. Use #[derive(RefCastCustom)] and #[ref_cast_custom].
 #[doc(hidden)]
 pub unsafe trait RefCastCustom<From: ?Sized> {
+    type CurrentCrate;
     fn __static_assert() {}
 }
 
-pub unsafe trait RefCastOkay<From> {}
+pub unsafe trait RefCastOkay<From>: Sealed<From> {
+    type CurrentCrate;
+    type Target: ?Sized;
+}
 
 unsafe impl<'a, From, To> RefCastOkay<&'a From> for &'a To
 where
     From: ?Sized,
     To: ?Sized + RefCastCustom<From>,
 {
+    type CurrentCrate = To::CurrentCrate;
+    type Target = To;
 }
 
 unsafe impl<'a, From, To> RefCastOkay<&'a mut From> for &'a mut To
+where
+    From: ?Sized,
+    To: ?Sized + RefCastCustom<From>,
+{
+    type CurrentCrate = To::CurrentCrate;
+    type Target = To;
+}
+
+pub trait Sealed<From> {}
+
+impl<'a, From, To> Sealed<&'a From> for &'a To
 where
     From: ?Sized,
     To: ?Sized + RefCastCustom<From>,
 {
 }
 
+impl<'a, From, To> Sealed<&'a mut From> for &'a mut To
+where
+    From: ?Sized,
+    To: ?Sized + RefCastCustom<From>,
+{
+}
+
+pub type CurrentCrate<From, To> = <To as RefCastOkay<From>>::CurrentCrate;
+
 pub fn ref_cast_custom<From, To>(_arg: From)
 where
     To: RefCastOkay<From>,

src/lib.rs

@@ -180,7 +180,7 @@ pub trait RefCast {
 // Not public API.
 #[doc(hidden)]
 pub mod __private {
-    pub use crate::custom::{ref_cast_custom, RefCastCustom};
+    pub use crate::custom::{ref_cast_custom, CurrentCrate, RefCastCustom};
     pub use crate::layout::{assert_layout, Layout, LayoutUnsized};
     pub use crate::trivial::assert_trivial;
     pub use core::mem::transmute;

tests/helper/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "ref-cast-test-suite"
+authors = ["David Tolnay <dtolnay@gmail.com>"]
+version = "0.0.0"
+edition = "2018"
+publish = false
+
+[lib]
+path = "lib.rs"
+
+[dependencies]
+ref-cast = "1"

tests/helper/lib.rs

@@ -0,0 +1,5 @@
+use ref_cast::RefCastCustom;
+
+#[derive(RefCastCustom)]
+#[repr(transparent)]
+pub struct Struct(str);

tests/ui/cross-crate.rs

@@ -0,0 +1,10 @@
+use ref_cast::ref_cast_custom;
+use ref_cast_test_suite::Struct;
+
+#[ref_cast_custom]
+fn ref_cast(s: &str) -> &Struct;
+
+#[ref_cast_custom]
+fn ref_cast_mut(s: &mut str) -> &mut Struct;
+
+fn main() {}

tests/ui/cross-crate.stderr

@@ -0,0 +1,11 @@
+error[E0639]: cannot create non-exhaustive struct using struct expression
+ --> tests/ui/cross-crate.rs:5:32
+  |
+5 | fn ref_cast(s: &str) -> &Struct;
+  |                                ^
+
+error[E0639]: cannot create non-exhaustive struct using struct expression
+ --> tests/ui/cross-crate.rs:8:44
+  |
+8 | fn ref_cast_mut(s: &mut str) -> &mut Struct;
+  |                                            ^

tests/ui/no-custom.stderr

@@ -13,3 +13,20 @@ note: required by a bound in `ref_cast_custom`
   |
   |     To: RefCastOkay<From>,
   |         ^^^^^^^^^^^^^^^^^ required by this bound in `ref_cast_custom`
+
+error[E0071]: expected struct, variant or union type, found inferred type
+ --> tests/ui/no-custom.rs:8:41
+  |
+8 |     pub fn ref_cast(s: &String) -> &Self;
+  |                                         ^ not a struct
+
+error[E0277]: the trait bound `Thing: RefCastCustom<String>` is not satisfied
+ --> tests/ui/no-custom.rs:8:41
+  |
+8 |     pub fn ref_cast(s: &String) -> &Self;
+  |                                         ^ the trait `RefCastCustom<String>` is not implemented for `Thing`
+  |
+  = help: the following other types implement trait `ref_cast::custom::RefCastOkay<From>`:
+            <&'a To as ref_cast::custom::RefCastOkay<&'a From>>
+            <&'a mut To as ref_cast::custom::RefCastOkay<&'a mut From>>
+  = note: required for `&Thing` to implement `ref_cast::custom::RefCastOkay<&String>`