Catch trybuild errors during monomorphization as well

crates/test-ui/src/hack.rs

@@ -0,0 +1 @@
+fn main() {}

crates/test-ui/src/main.rs

@@ -17,4 +17,12 @@ fn main() {
         .join("ui")
         .join("*.rs");
     t.compile_fail(path);
+    // Make trybuild use `cargo build` instead of `cargo check`
+    //
+    // Workaround for https://github.com/dtolnay/trybuild/issues/241
+    t.pass(
+        std::path::Path::new(env!("CARGO_MANIFEST_DIR"))
+            .join("src")
+            .join("hack.rs"),
+    );
 }

crates/test-ui/ui/invalid_option_encode_impl.rs

@@ -1,5 +1,5 @@
 //! Ensure that implementing `OptionEncode` wrongly results in an error
-use objc2::encode::{Encode, Encoding, OptionEncode, RefEncode};
+use objc2::encode::{Encode, Encoding, OptionEncode};
 
 #[repr(transparent)]
 struct MyType(usize);
@@ -8,19 +8,8 @@ unsafe impl Encode for MyType {
     const ENCODING: Encoding = usize::ENCODING;
 }
 
-unsafe impl RefEncode for MyType {
-    const ENCODING_REF: Encoding = usize::ENCODING_REF;
-}
-
 unsafe impl OptionEncode for MyType {}
 
 fn main() {
     assert_eq!(<Option<MyType>>::ENCODING, MyType::ENCODING);
-    assert_eq!(<Option<MyType>>::ENCODING_REF, MyType::ENCODING_REF);
-
-    // TODO: trybuild runs with `cargo check`, which doesn't catch all const
-    // errors.
-    const TODO: () = {
-        panic!("todo");
-    };
 }

crates/test-ui/ui/invalid_option_encode_impl.stderr

@@ -1,7 +1,21 @@
-error[E0080]: evaluation of constant value failed
- --> ui/invalid_option_encode_impl.rs
+error[E0080]: evaluation of `<std::option::Option<MyType> as objc2::Encode>::ENCODING` failed
+ --> $WORKSPACE/crates/objc2/src/encode/mod.rs
   |
-  |         panic!("todo");
-  |         ^^^^^^^^^^^^^^ the evaluated program panicked at 'todo', $DIR/ui/invalid_option_encode_impl.rs:24:9
+  |             panic!("invalid OptionEncode + Encode implementation");
+  |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'invalid OptionEncode + Encode implementation', $WORKSPACE/crates/objc2/src/encode/mod.rs:276:13
   |
   = note: this error originates in the macro `$crate::panic::panic_2021` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: erroneous constant used
+  --> ui/invalid_option_encode_impl.rs
+   |
+   |     assert_eq!(<Option<MyType>>::ENCODING, MyType::ENCODING);
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+note: erroneous constant used
+  --> ui/invalid_option_encode_impl.rs
+   |
+   |     assert_eq!(<Option<MyType>>::ENCODING, MyType::ENCODING);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this note originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)

crates/test-ui/ui/invalid_option_encode_impl_ref.rs

@@ -0,0 +1,15 @@
+//! Ensure that implementing `OptionEncode` wrongly results in an error
+use objc2::encode::{Encoding, OptionEncode, RefEncode};
+
+#[repr(transparent)]
+struct MyType(usize);
+
+unsafe impl RefEncode for MyType {
+    const ENCODING_REF: Encoding = usize::ENCODING_REF;
+}
+
+unsafe impl OptionEncode for MyType {}
+
+fn main() {
+    assert_eq!(<Option<MyType>>::ENCODING_REF, MyType::ENCODING_REF);
+}

crates/test-ui/ui/invalid_option_encode_impl_ref.stderr

@@ -0,0 +1,21 @@
+error[E0080]: evaluation of `<std::option::Option<MyType> as objc2::RefEncode>::ENCODING_REF` failed
+ --> $WORKSPACE/crates/objc2/src/encode/mod.rs
+  |
+  |             panic!("invalid OptionEncode + RefEncode implementation");
+  |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the evaluated program panicked at 'invalid OptionEncode + RefEncode implementation', $WORKSPACE/crates/objc2/src/encode/mod.rs:286:13
+  |
+  = note: this error originates in the macro `$crate::panic::panic_2021` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: erroneous constant used
+  --> ui/invalid_option_encode_impl_ref.rs
+   |
+   |     assert_eq!(<Option<MyType>>::ENCODING_REF, MyType::ENCODING_REF);
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+note: erroneous constant used
+  --> ui/invalid_option_encode_impl_ref.rs
+   |
+   |     assert_eq!(<Option<MyType>>::ENCODING_REF, MyType::ENCODING_REF);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this note originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info)