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clean up *dyn casts (with principals)

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- remove a redundant check, because we always emit the "better diagnostic" now
- clean up the comments a bit
This commit is contained in:
Lukas Markeffsky 2024-10-18 16:06:57 +02:00
parent 1350eead10
commit b89751b8f4
1 changed files with 8 additions and 14 deletions
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22
compiler/rustc_hir_typeck/src/cast.rs
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@ -876,20 +876,14 @@ impl<'a, 'tcx> CastCheck<'tcx> {
// A<dyn Src<...> + SrcAuto> -> B<dyn Dst<...> + DstAuto>. need to make sure
// - `Src` and `Dst` traits are the same
// - traits have the same generic arguments
// - `SrcAuto` is a superset of `DstAuto`
(Some(src_principal), Some(dst_principal)) => {
// - projections are the same
// - `SrcAuto` (+auto traits implied by `Src`) is a superset of `DstAuto`
//
// Note that trait upcasting goes through a different mechanism (`coerce_unsized`)
// and is unaffected by this check.
(Some(src_principal), Some(_)) => {
let tcx = fcx.tcx;
// Check that the traits are actually the same.
// The `dyn Src = dyn Dst` check below would suffice,
// but this may produce a better diagnostic.
//
// Note that trait upcasting goes through a different mechanism (`coerce_unsized`)
// and is unaffected by this check.
if src_principal.def_id() != dst_principal.def_id() {
return Err(CastError::DifferingKinds { src_kind, dst_kind });
}
// We need to reconstruct trait object types.
// `m_src` and `m_dst` won't work for us here because they will potentially
// contain wrappers, which we do not care about.
@ -912,8 +906,8 @@ impl<'a, 'tcx> CastCheck<'tcx> {
ty::Dyn,
));
// `dyn Src = dyn Dst`, this checks for matching traits/generics
// This is `demand_eqtype`, but inlined to give a better error.
// `dyn Src = dyn Dst`, this checks for matching traits/generics/projections
// This is `fcx.demand_eqtype`, but inlined to give a better error.
let cause = fcx.misc(self.span);
if fcx
.at(&cause, fcx.param_env)