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Prefer identity equality over equating types during coercion. #124027

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Apr 17, 2024
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Prefer identity equality over equating types during coercion. #124027

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35 changes: 13 additions & 22 deletions compiler/rustc_hir_analysis/src/coherence/builtin.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,8 @@ use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::lang_items::LangItem;
use rustc_hir::ItemKind;
use rustc_infer::infer::outlives::env::OutlivesEnvironment;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::infer::{self, RegionResolutionError};
use rustc_infer::infer::{DefineOpaqueTypes, TyCtxtInferExt};
use rustc_infer::traits::Obligation;
use rustc_middle::ty::adjustment::CoerceUnsizedInfo;
use rustc_middle::ty::{self, suggest_constraining_type_params, Ty, TyCtxt, TypeVisitableExt};
Expand Down Expand Up @@ -189,10 +189,7 @@ fn visit_implementation_of_dispatch_from_dyn(checker: &Checker<'_>) -> Result<()
// even if they do not carry that attribute.
use rustc_type_ir::TyKind::*;
match (source.kind(), target.kind()) {
(&Ref(r_a, _, mutbl_a), Ref(r_b, _, mutbl_b))
if infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, r_a, *r_b).is_ok()
&& mutbl_a == *mutbl_b =>
{
(&Ref(r_a, _, mutbl_a), Ref(r_b, _, mutbl_b)) if r_a == *r_b && mutbl_a == *mutbl_b => {
Ok(())
}
(&RawPtr(_, a_mutbl), &RawPtr(_, b_mutbl)) if a_mutbl == b_mutbl => Ok(()),
Expand Down Expand Up @@ -230,18 +227,14 @@ fn visit_implementation_of_dispatch_from_dyn(checker: &Checker<'_>) -> Result<()
}
}

if let Ok(ok) =
infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, ty_a, ty_b)
{
if ok.obligations.is_empty() {
res = Err(tcx.dcx().emit_err(errors::DispatchFromDynZST {
span,
name: field.name,
ty: ty_a,
}));
if ty_a == ty_b {
res = Err(tcx.dcx().emit_err(errors::DispatchFromDynZST {
span,
name: field.name,
ty: ty_a,
}));

return false;
}
return false;
}

return true;
Expand Down Expand Up @@ -433,14 +426,12 @@ pub fn coerce_unsized_info<'tcx>(
// something more accepting, but we use
// equality because we want to be able to
// perform this check without computing
// variance where possible. (This is because
// we may have to evaluate constraint
// variance or constraining opaque types' hidden types.
// (This is because we may have to evaluate constraint
// expressions in the course of execution.)
// See e.g., #41936.
if let Ok(ok) = infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, a, b) {
if ok.obligations.is_empty() {
return None;
}
if a == b {
return None;
}

// Collect up all fields that were significantly changed
Expand Down
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