Merge pull request #53 from dtolnay/supertrait

Detect missing supertrait on serialize_trait_object calls

Cargo.toml

@@ -15,9 +15,11 @@ rust-version = "1.31"
 serde = { version = "1.0.63", default-features = false }
 
 [dev-dependencies]
+rustversion = "1.0"
 serde_cbor = "0.11"
 serde_derive = "1.0"
 serde_json = "1.0"
+trybuild = { version = "1.0.49", features = ["diff"] }
 
 [features]
 # Note: at least one of "std" or "alloc" must be enabled.

src/macros.rs

@@ -79,14 +79,22 @@ macro_rules! __internal_serialize_trait_object {
 
     // Expand into four impls.
     (sendsync ($($generics:tt)*) ($($path:tt)*) ($($bound:tt)*)) => {
-        $crate::__internal_serialize_trait_object!(impl ($($generics)*) ($($path)*) ($($bound)*));
+        $crate::__internal_serialize_trait_object!(impl ($($generics)*) ($($path)*) ($($bound)*) {
+            fn __check_erased_serialize_supertrait<__T, $($generics)*>()
+            where
+                __T: ?$crate::private::Sized + $($path)*,
+                $($bound)*
+            {
+                $crate::private::require_erased_serialize_impl::<__T>();
+            }
+        });
         $crate::__internal_serialize_trait_object!(impl ($($generics)*) ($($path)* + $crate::private::Send) ($($bound)*));
         $crate::__internal_serialize_trait_object!(impl ($($generics)*) ($($path)* + $crate::private::Sync) ($($bound)*));
         $crate::__internal_serialize_trait_object!(impl ($($generics)*) ($($path)* + $crate::private::Send + $crate::private::Sync) ($($bound)*));
     };
 
     // The impl.
-    (impl ($($generics:tt)*) ($($path:tt)*) ($($bound:tt)*)) => {
+    (impl ($($generics:tt)*) ($($path:tt)*) ($($bound:tt)*) $({$($body:tt)*})*) => {
         impl<'erased, $($generics)*> $crate::private::serde::Serialize for dyn $($path)* + 'erased
         where
             $($bound)*
@@ -95,6 +103,7 @@ macro_rules! __internal_serialize_trait_object {
             where
                 S: $crate::private::serde::Serializer,
             {
+                $($($body)*)*
                 $crate::serialize(self, serializer)
             }
         }

src/private.rs

@@ -1,5 +1,11 @@
 //! Not public API. Used as `$crate::private` by macros.
 
-pub use core::marker::{Send, Sync};
+pub use core::marker::{Send, Sized, Sync};
 pub use core::result::Result;
 pub use serde;
+
+pub fn require_erased_serialize_impl<T>()
+where
+    T: ?Sized + crate::Serialize,
+{
+}

tests/compiletest.rs

@@ -0,0 +1,7 @@
+#[rustversion::attr(not(nightly), ignore)]
+#[cfg_attr(miri, ignore)]
+#[test]
+fn ui() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/ui/*.rs");
+}

tests/ui/missing-supertrait.rs

@@ -0,0 +1,7 @@
+use erased_serde::serialize_trait_object;
+
+pub trait MyTrait {}
+
+serialize_trait_object!(MyTrait);
+
+fn main() {}

tests/ui/missing-supertrait.stderr

@@ -0,0 +1,17 @@
+error[E0277]: the trait bound `__T: erased_serde::private::serde::Serialize` is not satisfied
+ --> tests/ui/missing-supertrait.rs:5:1
+  |
+5 | serialize_trait_object!(MyTrait);
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `erased_serde::private::serde::Serialize` is not implemented for `__T`
+  |
+  = note: required because of the requirements on the impl of `erased_serde::Serialize` for `__T`
+note: required by a bound in `require_erased_serialize_impl`
+ --> src/private.rs
+  |
+  |     T: ?Sized + crate::Serialize,
+  |                 ^^^^^^^^^^^^^^^^ required by this bound in `require_erased_serialize_impl`
+  = note: this error originates in the macro `$crate::__internal_serialize_trait_object` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider further restricting this bound
+  |
+85|                 __T + erased_serde::private::serde::Serialize: ?$crate::private::Sized + $($path)*,
+  |                     +++++++++++++++++++++++++++++++++++++++++