rewrite `ensure_drop_params_and_item_params_correspond`

6 files changed, 72 insertions, 127 deletions

diff --git a/compiler/rustc_typeck/src/check/dropck.rs b/compiler/rustc_typeck/src/check/dropck.rs
index 9caa4a40df7..0b0f7a085fc 100644
--- a/compiler/rustc_typeck/src/check/dropck.rs
+++ b/compiler/rustc_typeck/src/check/dropck.rs
@@ -2,17 +2,13 @@ use crate::check::regionck::RegionCtxt;
 use crate::hir;
 use crate::hir::def_id::{DefId, LocalDefId};
 use rustc_errors::{struct_span_err, ErrorGuaranteed};
-use rustc_infer::infer::outlives::env::OutlivesEnvironment;
-use rustc_infer::infer::{InferOk, RegionckMode, TyCtxtInferExt};
-use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation};
-use rustc_middle::ty::subst::{Subst, SubstsRef};
-use rustc_middle::ty::{self, EarlyBinder, Predicate, Ty, TyCtxt};
+use rustc_middle::ty::subst::SubstsRef;
+use rustc_middle::ty::{self, Predicate, Ty, TyCtxt};
 use rustc_span::Span;
-use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
 use rustc_trait_selection::traits::query::dropck_outlives::AtExt;
-use rustc_trait_selection::traits::{ObligationCause, TraitEngine, TraitEngineExt};
+use rustc_trait_selection::traits::ObligationCause;
 
 /// This function confirms that the `Drop` implementation identified by
 /// `drop_impl_did` is not any more specialized than the type it is
@@ -39,8 +35,8 @@ pub fn check_drop_impl(tcx: TyCtxt<'_>, drop_impl_did: DefId) -> Result<(), Erro
             ensure_drop_params_and_item_params_correspond(
                 tcx,
                 drop_impl_did.expect_local(),
-                dtor_self_type,
                 adt_def.did(),
+                self_to_impl_substs,
             )?;
 
             ensure_drop_predicates_are_implied_by_item_defn(
@@ -67,75 +63,34 @@ pub fn check_drop_impl(tcx: TyCtxt<'_>, drop_impl_did: DefId) -> Result<(), Erro
 fn ensure_drop_params_and_item_params_correspond<'tcx>(
     tcx: TyCtxt<'tcx>,
     drop_impl_did: LocalDefId,
-    drop_impl_ty: Ty<'tcx>,
     self_type_did: DefId,
+    drop_impl_substs: SubstsRef<'tcx>,
 ) -> Result<(), ErrorGuaranteed> {
-    let drop_impl_hir_id = tcx.hir().local_def_id_to_hir_id(drop_impl_did);
-
-    // check that the impl type can be made to match the trait type.
-
-    tcx.infer_ctxt().enter(|ref infcx| {
-        let impl_param_env = tcx.param_env(self_type_did);
-        let tcx = infcx.tcx;
-        let mut fulfillment_cx = <dyn TraitEngine<'_>>::new(tcx);
-
-        let named_type = tcx.type_of(self_type_did);
-
-        let drop_impl_span = tcx.def_span(drop_impl_did);
-        let fresh_impl_substs =
-            infcx.fresh_substs_for_item(drop_impl_span, drop_impl_did.to_def_id());
-        let fresh_impl_self_ty = EarlyBinder(drop_impl_ty).subst(tcx, fresh_impl_substs);
-
-        let cause = &ObligationCause::misc(drop_impl_span, drop_impl_hir_id);
-        match infcx.at(cause, impl_param_env).eq(named_type, fresh_impl_self_ty) {
-            Ok(InferOk { obligations, .. }) => {
-                fulfillment_cx.register_predicate_obligations(infcx, obligations);
-            }
-            Err(_) => {
-                let item_span = tcx.def_span(self_type_did);
-                let self_descr = tcx.def_kind(self_type_did).descr(self_type_did);
-                let reported = struct_span_err!(
-                    tcx.sess,
-                    drop_impl_span,
-                    E0366,
-                    "`Drop` impls cannot be specialized"
-                )
-                .span_note(
-                    item_span,
-                    &format!(
-                        "use the same sequence of generic type, lifetime and const parameters \
-                        as the {self_descr} definition",
-                    ),
-                )
-                .emit();
-                return Err(reported);
-            }
+    let Err(arg) = tcx.uses_unique_generic_params(drop_impl_substs, false) else {
+        return Ok(())
+    };
+
+    let drop_impl_span = tcx.def_span(drop_impl_did);
+    let item_span = tcx.def_span(self_type_did);
+    let self_descr = tcx.def_kind(self_type_did).descr(self_type_did);
+    let mut err =
+        struct_span_err!(tcx.sess, drop_impl_span, E0366, "`Drop` impls cannot be specialized");
+    match arg {
+        ty::util::NotUniqueParam::DuplicateParam(arg) => {
+            err.note(&format!("`{arg}` is mentioned multiple times"))
         }
-
-        let errors = fulfillment_cx.select_all_or_error(&infcx);
-        if !errors.is_empty() {
-            // this could be reached when we get lazy normalization
-            let reported = infcx.report_fulfillment_errors(&errors, None, false);
-            return Err(reported);
+        ty::util::NotUniqueParam::NotParam(arg) => {
+            err.note(&format!("`{arg}` is not a generic parameter"))
         }
-
-        // NB. It seems a bit... suspicious to use an empty param-env
-        // here. The correct thing, I imagine, would be
-        // `OutlivesEnvironment::new(impl_param_env)`, which would
-        // allow region solving to take any `a: 'b` relations on the
-        // impl into account. But I could not create a test case where
-        // it did the wrong thing, so I chose to preserve existing
-        // behavior, since it ought to be simply more
-        // conservative. -nmatsakis
-        let outlives_env = OutlivesEnvironment::new(ty::ParamEnv::empty());
-
-        infcx.resolve_regions_and_report_errors(
-            drop_impl_did.to_def_id(),
-            &outlives_env,
-            RegionckMode::default(),
-        );
-        Ok(())
-    })
+    };
+    err.span_note(
+        item_span,
+        &format!(
+            "use the same sequence of generic type, lifetime and const parameters \
+                     as the {self_descr} definition",
+        ),
+    );
+    Err(err.emit())
 }
 
 /// Confirms that every predicate imposed by dtor_predicates is
diff --git a/compiler/rustc_typeck/src/coherence/orphan.rs b/compiler/rustc_typeck/src/coherence/orphan.rs
index ad8a84d536f..f8b3f1ac3df 100644
--- a/compiler/rustc_typeck/src/coherence/orphan.rs
+++ b/compiler/rustc_typeck/src/coherence/orphan.rs
@@ -383,20 +383,13 @@ fn lint_auto_trait_impls(tcx: TyCtxt<'_>, trait_def_id: DefId, impls: &[LocalDef
             tcx.hir().local_def_id_to_hir_id(impl_def_id),
             tcx.def_span(impl_def_id),
             |err| {
+                let item_span = tcx.def_span(self_type_did);
+                let self_descr = tcx.def_kind(self_type_did).descr(self_type_did);
                 let mut err = err.build(&format!(
                     "cross-crate traits with a default impl, like `{}`, \
                          should not be specialized",
                     tcx.def_path_str(trait_def_id),
                 ));
-                let item_span = tcx.def_span(self_type_did);
-                let self_descr = tcx.def_kind(self_type_did).descr(self_type_did);
-                err.span_note(
-                    item_span,
-                    &format!(
-                        "try using the same sequence of generic parameters as the {} definition",
-                        self_descr,
-                    ),
-                );
                 match arg {
                     ty::util::NotUniqueParam::DuplicateParam(arg) => {
                         err.note(&format!("`{}` is mentioned multiple times", arg));
@@ -405,6 +398,13 @@ fn lint_auto_trait_impls(tcx: TyCtxt<'_>, trait_def_id: DefId, impls: &[LocalDef
                         err.note(&format!("`{}` is not a generic parameter", arg));
                     }
                 }
+                err.span_note(
+                    item_span,
+                    &format!(
+                        "try using the same sequence of generic parameters as the {} definition",
+                        self_descr,
+                    ),
+                );
                 err.emit();
             },
         );
diff --git a/src/test/ui/auto-traits/suspicious-impls-lint.stderr b/src/test/ui/auto-traits/suspicious-impls-lint.stderr
index e299e5369fe..03460b28dcd 100644
--- a/src/test/ui/auto-traits/suspicious-impls-lint.stderr
+++ b/src/test/ui/auto-traits/suspicious-impls-lint.stderr
@@ -11,12 +11,12 @@ LL | #![deny(suspicious_auto_trait_impls)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = warning: this will change its meaning in a future release!
    = note: for more information, see issue #93367 <https://github.com/rust-lang/rust/issues/93367>
+   = note: `&T` is not a generic parameter
 note: try using the same sequence of generic parameters as the struct definition
   --> $DIR/suspicious-impls-lint.rs:8:1
    |
 LL | struct MayImplementSendErr<T>(T);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: `&T` is not a generic parameter
 
 error: cross-crate traits with a default impl, like `Send`, should not be specialized
   --> $DIR/suspicious-impls-lint.rs:21:1
@@ -26,12 +26,12 @@ LL | unsafe impl Send for ContainsVec<i32> {}
    |
    = warning: this will change its meaning in a future release!
    = note: for more information, see issue #93367 <https://github.com/rust-lang/rust/issues/93367>
+   = note: `i32` is not a generic parameter
 note: try using the same sequence of generic parameters as the struct definition
   --> $DIR/suspicious-impls-lint.rs:20:1
    |
 LL | struct ContainsVec<T>(Vec<T>);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: `i32` is not a generic parameter
 
 error: cross-crate traits with a default impl, like `Send`, should not be specialized
   --> $DIR/suspicious-impls-lint.rs:32:1
@@ -41,12 +41,12 @@ LL | unsafe impl<T: Send> Send for TwoParamsSame<T, T> {}
    |
    = warning: this will change its meaning in a future release!
    = note: for more information, see issue #93367 <https://github.com/rust-lang/rust/issues/93367>
+   = note: `T` is mentioned multiple times
 note: try using the same sequence of generic parameters as the struct definition
   --> $DIR/suspicious-impls-lint.rs:31:1
    |
 LL | struct TwoParamsSame<T, U>(T, U);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: `T` is mentioned multiple times
 
 error: cross-crate traits with a default impl, like `Send`, should not be specialized
   --> $DIR/suspicious-impls-lint.rs:40:1
@@ -56,12 +56,12 @@ LL | unsafe impl<T> Send for WithPhantomDataSend<*const T, i8> {}
    |
    = warning: this will change its meaning in a future release!
    = note: for more information, see issue #93367 <https://github.com/rust-lang/rust/issues/93367>
+   = note: `*const T` is not a generic parameter
 note: try using the same sequence of generic parameters as the struct definition
   --> $DIR/suspicious-impls-lint.rs:39:1
    |
 LL | pub struct WithPhantomDataSend<T, U>(PhantomData<T>, U);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: `*const T` is not a generic parameter
 
 error: cross-crate traits with a default impl, like `Sync`, should not be specialized
   --> $DIR/suspicious-impls-lint.rs:46:1
@@ -71,12 +71,12 @@ LL | unsafe impl<T> Sync for WithLifetime<'static, Vec<T>> {}
    |
    = warning: this will change its meaning in a future release!
    = note: for more information, see issue #93367 <https://github.com/rust-lang/rust/issues/93367>
+   = note: `Vec<T>` is not a generic parameter
 note: try using the same sequence of generic parameters as the struct definition
   --> $DIR/suspicious-impls-lint.rs:44:1
    |
 LL | pub struct WithLifetime<'a, T>(&'a (), T);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: `Vec<T>` is not a generic parameter
 
 error: aborting due to 5 previous errors
 
diff --git a/src/test/ui/dropck/issue-38868.stderr b/src/test/ui/dropck/issue-38868.stderr
index 10d1e7c4e66..f369b74cf55 100644
--- a/src/test/ui/dropck/issue-38868.stderr
+++ b/src/test/ui/dropck/issue-38868.stderr
@@ -8,6 +8,7 @@ LL | |     }
 LL | | }
    | |_^
    |
+   = note: `i32` is not a generic parameter
 note: use the same sequence of generic type, lifetime and const parameters as the struct definition
   --> $DIR/issue-38868.rs:1:1
    |
diff --git a/src/test/ui/dropck/reject-specialized-drops-8142.rs b/src/test/ui/dropck/reject-specialized-drops-8142.rs
index c9599f6e805..7a3bbe7cb09 100644
--- a/src/test/ui/dropck/reject-specialized-drops-8142.rs
+++ b/src/test/ui/dropck/reject-specialized-drops-8142.rs
@@ -32,9 +32,7 @@ impl<'al,'adds_bnd>     Drop for L<'al,'adds_bnd> where 'adds_bnd:'al {    // RE
 impl<'ml>               Drop for M<'ml>         { fn drop(&mut self) { } } // ACCEPT
 
 impl                    Drop for N<'static>     { fn drop(&mut self) { } } // REJECT
-//~^ ERROR mismatched types
-//~| expected struct `N<'n>`
-//~|    found struct `N<'static>`
+//~^ ERROR `Drop` impls cannot be specialized
 
 impl<COkNoBound> Drop for O<COkNoBound> { fn drop(&mut self) { } } // ACCEPT
 
@@ -57,7 +55,7 @@ impl<One>         Drop for V<One,One>     { fn drop(&mut self) { } } // REJECT
 //~^ ERROR `Drop` impls cannot be specialized
 
 impl<'lw>         Drop for W<'lw,'lw>     { fn drop(&mut self) { } } // REJECT
-//~^ ERROR cannot infer an appropriate lifetime for lifetime parameter `'lw`
+//~^ ERROR `Drop` impls cannot be specialized
 
 impl              Drop for X<3>           { fn drop(&mut self) { } } // REJECT
 //~^ ERROR `Drop` impls cannot be specialized
diff --git a/src/test/ui/dropck/reject-specialized-drops-8142.stderr b/src/test/ui/dropck/reject-specialized-drops-8142.stderr
index 8dbde9d417d..82e95ea075d 100644
--- a/src/test/ui/dropck/reject-specialized-drops-8142.stderr
+++ b/src/test/ui/dropck/reject-specialized-drops-8142.stderr
@@ -22,27 +22,26 @@ note: the implementor must specify the same requirement
 LL | struct L<'l1,'l2> { x: &'l1 i8, y: &'l2 u8 }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0308]: mismatched types
+error[E0366]: `Drop` impls cannot be specialized
   --> $DIR/reject-specialized-drops-8142.rs:34:1
    |
 LL | impl                    Drop for N<'static>     { fn drop(&mut self) { } } // REJECT
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: expected struct `N<'n>`
-              found struct `N<'static>`
-note: the lifetime `'n` as defined here...
-  --> $DIR/reject-specialized-drops-8142.rs:7:10
+   = note: `'static` is not a generic parameter
+note: use the same sequence of generic type, lifetime and const parameters as the struct definition
+  --> $DIR/reject-specialized-drops-8142.rs:7:1
    |
 LL | struct N<'n> { x: &'n i8 }
-   |          ^^
-   = note: ...does not necessarily outlive the static lifetime
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0366]: `Drop` impls cannot be specialized
-  --> $DIR/reject-specialized-drops-8142.rs:41:1
+  --> $DIR/reject-specialized-drops-8142.rs:39:1
    |
 LL | impl              Drop for P<i8>          { fn drop(&mut self) { } } // REJECT
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
+   = note: `i8` is not a generic parameter
 note: use the same sequence of generic type, lifetime and const parameters as the struct definition
   --> $DIR/reject-specialized-drops-8142.rs:9:1
    |
@@ -50,7 +49,7 @@ LL | struct P<Tp> { x: *const Tp }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0367]: `Drop` impl requires `AddsBnd: Bound` but the struct it is implemented for does not
-  --> $DIR/reject-specialized-drops-8142.rs:44:14
+  --> $DIR/reject-specialized-drops-8142.rs:42:14
    |
 LL | impl<AddsBnd:Bound> Drop for Q<AddsBnd> { fn drop(&mut self) { } } // REJECT
    |              ^^^^^
@@ -62,7 +61,7 @@ LL | struct Q<Tq> { x: *const Tq }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0367]: `Drop` impl requires `AddsRBnd: 'rbnd` but the struct it is implemented for does not
-  --> $DIR/reject-specialized-drops-8142.rs:47:21
+  --> $DIR/reject-specialized-drops-8142.rs:45:21
    |
 LL | impl<'rbnd,AddsRBnd:'rbnd> Drop for R<AddsRBnd> { fn drop(&mut self) { } } // REJECT
    |                     ^^^^^
@@ -74,47 +73,38 @@ LL | struct R<Tr> { x: *const Tr }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0366]: `Drop` impls cannot be specialized
-  --> $DIR/reject-specialized-drops-8142.rs:56:1
+  --> $DIR/reject-specialized-drops-8142.rs:54:1
    |
 LL | impl<One>         Drop for V<One,One>     { fn drop(&mut self) { } } // REJECT
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
+   = note: `One` is mentioned multiple times
 note: use the same sequence of generic type, lifetime and const parameters as the struct definition
   --> $DIR/reject-specialized-drops-8142.rs:15:1
    |
 LL | struct V<Tva, Tvb> { x: *const Tva, y: *const Tvb }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'lw` due to conflicting requirements
-  --> $DIR/reject-specialized-drops-8142.rs:59:1
+error[E0366]: `Drop` impls cannot be specialized
+  --> $DIR/reject-specialized-drops-8142.rs:57:1
    |
 LL | impl<'lw>         Drop for W<'lw,'lw>     { fn drop(&mut self) { } } // REJECT
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-note: first, the lifetime cannot outlive the lifetime `'l1` as defined here...
-  --> $DIR/reject-specialized-drops-8142.rs:16:10
-   |
-LL | struct W<'l1, 'l2> { x: &'l1 i8, y: &'l2 u8 }
-   |          ^^^
-note: ...but the lifetime must also be valid for the lifetime `'l2` as defined here...
-  --> $DIR/reject-specialized-drops-8142.rs:16:15
+   = note: `'lw` is mentioned multiple times
+note: use the same sequence of generic type, lifetime and const parameters as the struct definition
+  --> $DIR/reject-specialized-drops-8142.rs:16:1
    |
 LL | struct W<'l1, 'l2> { x: &'l1 i8, y: &'l2 u8 }
-   |               ^^^
-note: ...so that the types are compatible
-  --> $DIR/reject-specialized-drops-8142.rs:59:1
-   |
-LL | impl<'lw>         Drop for W<'lw,'lw>     { fn drop(&mut self) { } } // REJECT
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: expected `W<'l1, 'l2>`
-              found `W<'_, '_>`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0366]: `Drop` impls cannot be specialized
-  --> $DIR/reject-specialized-drops-8142.rs:62:1
+  --> $DIR/reject-specialized-drops-8142.rs:60:1
    |
 LL | impl              Drop for X<3>           { fn drop(&mut self) { } } // REJECT
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
+   = note: `3_usize` is not a generic parameter
 note: use the same sequence of generic type, lifetime and const parameters as the struct definition
   --> $DIR/reject-specialized-drops-8142.rs:17:1
    |
@@ -122,11 +112,12 @@ LL | struct X<const Ca: usize>;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0366]: `Drop` impls cannot be specialized
-  --> $DIR/reject-specialized-drops-8142.rs:65:1
+  --> $DIR/reject-specialized-drops-8142.rs:63:1
    |
 LL | impl<const Ca: usize> Drop for Y<Ca, Ca>     { fn drop(&mut self) { } } // REJECT
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
+   = note: `Ca` is mentioned multiple times
 note: use the same sequence of generic type, lifetime and const parameters as the struct definition
   --> $DIR/reject-specialized-drops-8142.rs:18:1
    |
@@ -134,7 +125,7 @@ LL | struct Y<const Ca: usize, const Cb: usize>;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0367]: `Drop` impl requires `AddsBnd: Bound` but the enum it is implemented for does not
-  --> $DIR/reject-specialized-drops-8142.rs:68:14
+  --> $DIR/reject-specialized-drops-8142.rs:66:14
    |
 LL | impl<AddsBnd:Bound> Drop for Enum<AddsBnd> { fn drop(&mut self) { } } // REJECT
    |              ^^^^^
@@ -146,7 +137,7 @@ LL | enum Enum<T> { Variant(T) }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0367]: `Drop` impl requires `AddsBnd: Bound` but the struct it is implemented for does not
-  --> $DIR/reject-specialized-drops-8142.rs:71:14
+  --> $DIR/reject-specialized-drops-8142.rs:69:14
    |
 LL | impl<AddsBnd:Bound> Drop for TupleStruct<AddsBnd> { fn drop(&mut self) { } } // REJECT
    |              ^^^^^
@@ -158,7 +149,7 @@ LL | struct TupleStruct<T>(T);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0367]: `Drop` impl requires `AddsBnd: Bound` but the union it is implemented for does not
-  --> $DIR/reject-specialized-drops-8142.rs:74:21
+  --> $DIR/reject-specialized-drops-8142.rs:72:21
    |
 LL | impl<AddsBnd:Copy + Bound> Drop for Union<AddsBnd> { fn drop(&mut self) { } } // REJECT
    |                     ^^^^^
@@ -171,5 +162,5 @@ LL | union Union<T: Copy> { f: T }
 
 error: aborting due to 13 previous errors
 
-Some errors have detailed explanations: E0308, E0366, E0367, E0495.
-For more information about an error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0366, E0367.
+For more information about an error, try `rustc --explain E0366`.