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Mention traits being upcasted, types being coerced

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This commit is contained in:
Michael Goulet 2022-04-24 21:07:46 -07:00
parent 4c5f6e6277
commit 0de7568e41
3 changed files with 16 additions and 9 deletions
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19
compiler/rustc_typeck/src/check/coercion.rs
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@ -615,7 +615,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
)];
let mut has_unsized_tuple_coercion = false;
let mut has_trait_upcasting_coercion = false;
let mut has_trait_upcasting_coercion = None;
// Keep resolving `CoerceUnsized` and `Unsize` predicates to avoid
// emitting a coercion in cases like `Foo<$1>` -> `Foo<$2>`, where
@ -635,7 +635,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
&& data_a.principal_def_id() != data_b.principal_def_id()
{
debug!("coerce_unsized: found trait upcasting coercion");
has_trait_upcasting_coercion = true;
has_trait_upcasting_coercion = Some((self_ty, unsize_ty));
}
if let ty::Tuple(..) = unsize_ty.kind() {
debug!("coerce_unsized: found unsized tuple coercion");
@ -706,14 +706,19 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
.emit();
}
if has_trait_upcasting_coercion && !self.tcx().features().trait_upcasting {
feature_err(
if let Some((sub, sup)) = has_trait_upcasting_coercion
&& !self.tcx().features().trait_upcasting
{
// Renders better when we erase regions, since they're not really the point here.
let (sub, sup) = self.tcx.erase_regions((sub, sup));
let mut err = feature_err(
&self.tcx.sess.parse_sess,
sym::trait_upcasting,
self.cause.span,
"trait upcasting coercion is experimental",
)
.emit();
&format!("cannot cast `{sub}` to `{sup}`, trait upcasting coercion is experimental"),
);
err.note(&format!("required when coercing `{source}` into `{target}`"));
err.emit();
}
Ok(coercion)