Clean up error message for deferred assertions

Author: meithecatte

enumflags_derive/src/lib.rs

@@ -135,16 +135,16 @@ fn verify_flag_values<'a>(
                     &format!("__enumflags_assertion_{}_{}",
                             type_name, variant_name),
                     Span::call_site()); // call_site because def_site is unstable
-                // adapted from static-assertions-rs by nvzqz (MIT/Apache-2.0)
+
                 deferred_checks.push(quote_spanned!(variant.span() =>
                     #[doc(hidden)]
-                    const #assertion_name: fn() = || {
-                        ::enumflags2::_internal::assert_exactly_one_bit_set::<[(); (
+                    const #assertion_name:
+                        <<[(); (
                             (#type_name::#variant_name as u64).wrapping_sub(1) &
                             (#type_name::#variant_name as u64) == 0 &&
                             (#type_name::#variant_name as u64) != 0
-                        ) as usize]>();
-                    };
+                        ) as usize] as enumflags2::_internal::AssertionHelper>
+                            ::Status as enumflags2::_internal::ExactlyOneBitSet>::X = ();
                 ));
             }
         }

src/lib.rs

@@ -209,8 +209,12 @@ pub mod _internal {
 
     pub struct AssertionSucceeded;
     pub struct AssertionFailed;
-    pub trait ExactlyOneBitSet {}
-    impl ExactlyOneBitSet for AssertionSucceeded {}
+    pub trait ExactlyOneBitSet {
+        type X;
+    }
+    impl ExactlyOneBitSet for AssertionSucceeded {
+        type X = ();
+    }
 
     pub trait AssertionHelper {
         type Status;
@@ -223,9 +227,6 @@ pub mod _internal {
     impl AssertionHelper for [(); 0] {
         type Status = AssertionFailed;
     }
-
-    pub fn assert_exactly_one_bit_set<Assertion: AssertionHelper>()
-        where Assertion::Status: ExactlyOneBitSet {}
 }
 
 // Internal debug formatting implementations

test_suite/ui/multiple_bits_deferred.stderr

@@ -1,10 +1,5 @@
 error[E0277]: the trait bound `enumflags2::_internal::AssertionFailed: enumflags2::_internal::ExactlyOneBitSet` is not satisfied
-   --> $DIR/multiple_bits_deferred.rs:6:5
-    |
-6   |     Three = THREE,
-    |     ^^^^^ the trait `enumflags2::_internal::ExactlyOneBitSet` is not implemented for `enumflags2::_internal::AssertionFailed`
-    |
-   ::: $WORKSPACE/src/lib.rs:228:34
-    |
-228 |         where Assertion::Status: ExactlyOneBitSet {}
-    |                                  ---------------- required by this bound in `enumflags2::_internal::assert_exactly_one_bit_set`
+ --> $DIR/multiple_bits_deferred.rs:6:5
+  |
+6 |     Three = THREE,
+  |     ^^^^^ the trait `enumflags2::_internal::ExactlyOneBitSet` is not implemented for `enumflags2::_internal::AssertionFailed`