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Explain what the heck is going on with this lifetime remapping business

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This commit is contained in:
Oli Scherer 2023-07-21 14:28:22 +00:00
parent 44e21503a8
commit 10d0ff975c
1 changed files with 12 additions and 5 deletions
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17
compiler/rustc_hir_analysis/src/check/check.rs
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@ -504,12 +504,18 @@ fn sanity_check_found_hidden_type<'tcx>(
_ => l, _ => l,
}, },
}); });
// Get the hidden type, and in case it is in a nested opaque type, find that opaque type's // Get the hidden type.
// usage in the function signature and use the generic arguments from the usage site.
let mut hidden_ty = tcx.type_of(key.def_id).instantiate(tcx, key.args); let mut hidden_ty = tcx.type_of(key.def_id).instantiate(tcx, key.args);
// In case it is in a nested opaque type, find that opaque type's
// usage in the function signature and use the generic arguments from the usage site.
// We need to do because RPITs ignore the lifetimes of the function,
// as they have their own copies of all the lifetimes they capture.
// So the only way to get the lifetimes represented in terms of the function,
// is to look how they are used in the function signature (or do some other fancy
// recording of this mapping at ast -> hir lowering time).
if let hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..) = origin { if let hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..) = origin {
if hidden_ty != ty.ty { if hidden_ty != ty.ty {
hidden_ty = find_and_apply_rpit_substs( hidden_ty = find_and_apply_rpit_args(
tcx, tcx,
hidden_ty, hidden_ty,
defining_use_anchor.to_def_id(), defining_use_anchor.to_def_id(),
@ -517,6 +523,7 @@ fn sanity_check_found_hidden_type<'tcx>(
)?; )?;
} }
} }
// If the hidden types differ, emit a type mismatch diagnostic. // If the hidden types differ, emit a type mismatch diagnostic.
if hidden_ty == ty.ty { if hidden_ty == ty.ty {
Ok(()) Ok(())
@ -527,13 +534,13 @@ fn sanity_check_found_hidden_type<'tcx>(
} }
} }
fn find_and_apply_rpit_substs<'tcx>( fn find_and_apply_rpit_args<'tcx>(
tcx: TyCtxt<'tcx>, tcx: TyCtxt<'tcx>,
mut hidden_ty: Ty<'tcx>, mut hidden_ty: Ty<'tcx>,
function: DefId, function: DefId,
opaque: DefId, opaque: DefId,
) -> Result<Ty<'tcx>, ErrorGuaranteed> { ) -> Result<Ty<'tcx>, ErrorGuaranteed> {
// Find use of the RPIT in the function signature and thus find the right substs to // Find use of the RPIT in the function signature and thus find the right args to
// convert it into the parameter space of the function signature. This is needed, // convert it into the parameter space of the function signature. This is needed,
// because that's what `type_of` returns, against which we compare later. // because that's what `type_of` returns, against which we compare later.
let ret = tcx.fn_sig(function).instantiate_identity().output(); let ret = tcx.fn_sig(function).instantiate_identity().output();