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Clean up infer_return_ty_for_fn_sig #134259

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Dec 15, 2024
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Clean up infer_return_ty_for_fn_sig #134259

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179 changes: 94 additions & 85 deletions compiler/rustc_hir_analysis/src/collect.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1330,7 +1330,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, ty::PolyFn
..
})
| Item(hir::Item { kind: ItemKind::Fn(sig, generics, _), .. }) => {
infer_return_ty_for_fn_sig(sig, generics, def_id, &icx)
lower_fn_sig_recovering_infer_ret_ty(&icx, sig, generics, def_id)
}

ImplItem(hir::ImplItem { kind: ImplItemKind::Fn(sig, _), generics, .. }) => {
Expand All @@ -1347,7 +1347,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, ty::PolyFn
None,
)
} else {
infer_return_ty_for_fn_sig(sig, generics, def_id, &icx)
lower_fn_sig_recovering_infer_ret_ty(&icx, sig, generics, def_id)
}
}

Expand Down Expand Up @@ -1397,99 +1397,108 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, ty::PolyFn
ty::EarlyBinder::bind(output)
}

fn infer_return_ty_for_fn_sig<'tcx>(
sig: &hir::FnSig<'tcx>,
generics: &hir::Generics<'_>,
fn lower_fn_sig_recovering_infer_ret_ty<'tcx>(
icx: &ItemCtxt<'tcx>,
sig: &'tcx hir::FnSig<'tcx>,
generics: &'tcx hir::Generics<'tcx>,
def_id: LocalDefId,
) -> ty::PolyFnSig<'tcx> {
if let Some(infer_ret_ty) = sig.decl.output.get_infer_ret_ty() {
return recover_infer_ret_ty(icx, infer_ret_ty, generics, def_id);
}

icx.lowerer().lower_fn_ty(
icx.tcx().local_def_id_to_hir_id(def_id),
sig.header.safety,
sig.header.abi,
sig.decl,
Some(generics),
None,
)
}

fn recover_infer_ret_ty<'tcx>(
icx: &ItemCtxt<'tcx>,
infer_ret_ty: &'tcx hir::Ty<'tcx>,
generics: &'tcx hir::Generics<'tcx>,
def_id: LocalDefId,
) -> ty::PolyFnSig<'tcx> {
let tcx = icx.tcx;
let hir_id = tcx.local_def_id_to_hir_id(def_id);

match sig.decl.output.get_infer_ret_ty() {
Some(ty) => {
let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];
// Typeck doesn't expect erased regions to be returned from `type_of`.
// This is a heuristic approach. If the scope has region parameters,
// we should change fn_sig's lifetime from `ReErased` to `ReError`,
// otherwise to `ReStatic`.
let has_region_params = generics.params.iter().any(|param| match param.kind {
GenericParamKind::Lifetime { .. } => true,
_ => false,
});
let fn_sig = fold_regions(tcx, fn_sig, |r, _| match *r {
ty::ReErased => {
if has_region_params {
ty::Region::new_error_with_message(
tcx,
DUMMY_SP,
"erased region is not allowed here in return type",
)
} else {
tcx.lifetimes.re_static
}
}
_ => r,
});
let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];

let mut visitor = HirPlaceholderCollector::default();
visitor.visit_ty(ty);

let mut diag = bad_placeholder(icx.lowerer(), visitor.0, "return type");
let ret_ty = fn_sig.output();
// Don't leak types into signatures unless they're nameable!
// For example, if a function returns itself, we don't want that
// recursive function definition to leak out into the fn sig.
let mut recovered_ret_ty = None;

if let Some(suggestable_ret_ty) = ret_ty.make_suggestable(tcx, false, None) {
diag.span_suggestion(
ty.span,
"replace with the correct return type",
suggestable_ret_ty,
Applicability::MachineApplicable,
);
recovered_ret_ty = Some(suggestable_ret_ty);
} else if let Some(sugg) = suggest_impl_trait(
&tcx.infer_ctxt().build(TypingMode::non_body_analysis()),
tcx.param_env(def_id),
ret_ty,
) {
diag.span_suggestion(
ty.span,
"replace with an appropriate return type",
sugg,
Applicability::MachineApplicable,
);
} else if ret_ty.is_closure() {
diag.help("consider using an `Fn`, `FnMut`, or `FnOnce` trait bound");
}
// Also note how `Fn` traits work just in case!
if ret_ty.is_closure() {
diag.note(
"for more information on `Fn` traits and closure types, see \
https://doc.rust-lang.org/book/ch13-01-closures.html",
);
// Typeck doesn't expect erased regions to be returned from `type_of`.
// This is a heuristic approach. If the scope has region parameters,
// we should change fn_sig's lifetime from `ReErased` to `ReError`,
// otherwise to `ReStatic`.
let has_region_params = generics.params.iter().any(|param| match param.kind {
GenericParamKind::Lifetime { .. } => true,
_ => false,
});
let fn_sig = fold_regions(tcx, fn_sig, |r, _| match *r {
ty::ReErased => {
if has_region_params {
ty::Region::new_error_with_message(
tcx,
DUMMY_SP,
"erased region is not allowed here in return type",
)
} else {
tcx.lifetimes.re_static
}

let guar = diag.emit();
ty::Binder::dummy(tcx.mk_fn_sig(
fn_sig.inputs().iter().copied(),
recovered_ret_ty.unwrap_or_else(|| Ty::new_error(tcx, guar)),
fn_sig.c_variadic,
fn_sig.safety,
fn_sig.abi,
))
}
None => icx.lowerer().lower_fn_ty(
hir_id,
sig.header.safety,
sig.header.abi,
sig.decl,
Some(generics),
None,
),
_ => r,
});

let mut visitor = HirPlaceholderCollector::default();
visitor.visit_ty(infer_ret_ty);

let mut diag = bad_placeholder(icx.lowerer(), visitor.0, "return type");
let ret_ty = fn_sig.output();

// Don't leak types into signatures unless they're nameable!
// For example, if a function returns itself, we don't want that
// recursive function definition to leak out into the fn sig.
let mut recovered_ret_ty = None;
if let Some(suggestable_ret_ty) = ret_ty.make_suggestable(tcx, false, None) {
diag.span_suggestion(
infer_ret_ty.span,
"replace with the correct return type",
suggestable_ret_ty,
Applicability::MachineApplicable,
);
recovered_ret_ty = Some(suggestable_ret_ty);
} else if let Some(sugg) = suggest_impl_trait(
&tcx.infer_ctxt().build(TypingMode::non_body_analysis()),
tcx.param_env(def_id),
ret_ty,
) {
diag.span_suggestion(
infer_ret_ty.span,
"replace with an appropriate return type",
sugg,
Applicability::MachineApplicable,
);
} else if ret_ty.is_closure() {
diag.help("consider using an `Fn`, `FnMut`, or `FnOnce` trait bound");
}

// Also note how `Fn` traits work just in case!
if ret_ty.is_closure() {
diag.note(
"for more information on `Fn` traits and closure types, see \
https://doc.rust-lang.org/book/ch13-01-closures.html",
);
}
let guar = diag.emit();
ty::Binder::dummy(tcx.mk_fn_sig(
fn_sig.inputs().iter().copied(),
recovered_ret_ty.unwrap_or_else(|| Ty::new_error(tcx, guar)),
fn_sig.c_variadic,
fn_sig.safety,
fn_sig.abi,
))
}

pub fn suggest_impl_trait<'tcx>(
Expand Down
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