diff options
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/misc.rs | 4 | ||||
| -rw-r--r-- | compiler/rustc_typeck/src/coherence/builtin.rs | 36 | ||||
| -rw-r--r-- | src/test/ui/coherence/deep-bad-copy-reason.rs | 40 | ||||
| -rw-r--r-- | src/test/ui/coherence/deep-bad-copy-reason.stderr | 18 | ||||
| -rw-r--r-- | src/test/ui/union/union-copy.stderr | 6 |
5 files changed, 100 insertions, 4 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/misc.rs b/compiler/rustc_trait_selection/src/traits/misc.rs index 08308253ced..b83b0bf1ca5 100644 --- a/compiler/rustc_trait_selection/src/traits/misc.rs +++ b/compiler/rustc_trait_selection/src/traits/misc.rs @@ -11,7 +11,7 @@ use crate::traits::error_reporting::InferCtxtExt; #[derive(Clone)] pub enum CopyImplementationError<'tcx> { - InfrigingFields(Vec<&'tcx ty::FieldDef>), + InfrigingFields(Vec<(&'tcx ty::FieldDef, Ty<'tcx>)>), NotAnAdt, HasDestructor, } @@ -67,7 +67,7 @@ pub fn can_type_implement_copy<'tcx>( match traits::fully_normalize(&infcx, ctx, cause, param_env, ty) { Ok(ty) => { if !infcx.type_is_copy_modulo_regions(param_env, ty, span) { - infringing.push(field); + infringing.push((field, ty)); } } Err(errors) => { diff --git a/compiler/rustc_typeck/src/coherence/builtin.rs b/compiler/rustc_typeck/src/coherence/builtin.rs index ef59df0dc88..3135e9996ab 100644 --- a/compiler/rustc_typeck/src/coherence/builtin.rs +++ b/compiler/rustc_typeck/src/coherence/builtin.rs @@ -91,8 +91,40 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) { E0204, "the trait `Copy` may not be implemented for this type" ); - for span in fields.iter().map(|f| tcx.def_span(f.did)) { - err.span_label(span, "this field does not implement `Copy`"); + for (field, ty) in fields { + let field_span = tcx.def_span(field.did); + err.span_label(field_span, "this field does not implement `Copy`"); + // Spin up a new FulfillmentContext, so we can get the _precise_ reason + // why this field does not implement Copy. This is useful because sometimes + // it is not immediately clear why Copy is not implemented for a field, since + // all we point at is the field itself. + tcx.infer_ctxt().enter(|infcx| { + let mut fulfill_cx = traits::FulfillmentContext::new_ignoring_regions(); + fulfill_cx.register_bound( + &infcx, + param_env, + ty, + tcx.lang_items().copy_trait().unwrap(), + traits::ObligationCause::dummy_with_span(field_span), + ); + for error in fulfill_cx.select_all_or_error(&infcx) { + let error_predicate = error.obligation.predicate; + // Only note if it's not the root obligation, otherwise it's trivial and + // should be self-explanatory (i.e. a field literally doesn't implement Copy). + + // FIXME: This error could be more descriptive, especially if the error_predicate + // contains a foreign type or if it's a deeply nested type... + if error_predicate != error.root_obligation.predicate { + err.span_note( + error.obligation.cause.span, + &format!( + "the `Copy` impl for `{}` requires that `{}`", + ty, error_predicate + ), + ); + } + } + }); } err.emit(); } diff --git a/src/test/ui/coherence/deep-bad-copy-reason.rs b/src/test/ui/coherence/deep-bad-copy-reason.rs new file mode 100644 index 00000000000..80bbe387ac7 --- /dev/null +++ b/src/test/ui/coherence/deep-bad-copy-reason.rs @@ -0,0 +1,40 @@ +#![feature(extern_types)] + +extern "Rust" { + type OpaqueListContents; +} + +pub struct ListS<T> { + len: usize, + data: [T; 0], + opaque: OpaqueListContents, +} + +pub struct Interned<'a, T>(&'a T); + +impl<'a, T> Clone for Interned<'a, T> { + fn clone(&self) -> Self { + *self + } +} + +impl<'a, T> Copy for Interned<'a, T> {} + +pub struct List<'tcx, T>(Interned<'tcx, ListS<T>>); +//~^ NOTE this field does not implement `Copy` +//~| NOTE the `Copy` impl for `Interned<'tcx, ListS<T>>` requires that `OpaqueListContents: Sized` + +impl<'tcx, T> Clone for List<'tcx, T> { + fn clone(&self) -> Self { + *self + } +} + +impl<'tcx, T> Copy for List<'tcx, T> {} +//~^ ERROR the trait `Copy` may not be implemented for this type + +fn assert_is_copy<T: Copy>() {} + +fn main() { + assert_is_copy::<List<'static, ()>>(); +} diff --git a/src/test/ui/coherence/deep-bad-copy-reason.stderr b/src/test/ui/coherence/deep-bad-copy-reason.stderr new file mode 100644 index 00000000000..295538cee60 --- /dev/null +++ b/src/test/ui/coherence/deep-bad-copy-reason.stderr @@ -0,0 +1,18 @@ +error[E0204]: the trait `Copy` may not be implemented for this type + --> $DIR/deep-bad-copy-reason.rs:33:15 + | +LL | pub struct List<'tcx, T>(Interned<'tcx, ListS<T>>); + | ------------------------ this field does not implement `Copy` +... +LL | impl<'tcx, T> Copy for List<'tcx, T> {} + | ^^^^ + | +note: the `Copy` impl for `Interned<'tcx, ListS<T>>` requires that `OpaqueListContents: Sized` + --> $DIR/deep-bad-copy-reason.rs:23:26 + | +LL | pub struct List<'tcx, T>(Interned<'tcx, ListS<T>>); + | ^^^^^^^^^^^^^^^^^^^^^^^^ + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0204`. diff --git a/src/test/ui/union/union-copy.stderr b/src/test/ui/union/union-copy.stderr index 0f47bae7f0f..279808dd55b 100644 --- a/src/test/ui/union/union-copy.stderr +++ b/src/test/ui/union/union-copy.stderr @@ -6,6 +6,12 @@ LL | a: std::mem::ManuallyDrop<String> ... LL | impl Copy for W {} | ^^^^ + | +note: the `Copy` impl for `ManuallyDrop<String>` requires that `String: Copy` + --> $DIR/union-copy.rs:8:5 + | +LL | a: std::mem::ManuallyDrop<String> + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: aborting due to previous error |