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Check const_eval_select intrinsic correctly
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@compiler-errors
compiler-errors committed Dec 18, 2023
1 parent 69f360d commit faea6ad
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Showing 4 changed files with 81 additions and 46 deletions.
59 changes: 59 additions & 0 deletions compiler/rustc_hir_typeck/src/callee.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -471,6 +471,65 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}
}

if let Some(def_id) = def_id
&& self.tcx.def_kind(def_id) == hir::def::DefKind::Fn
&& self.tcx.is_intrinsic(def_id)
&& self.tcx.item_name(def_id) == sym::const_eval_select
{
let fn_sig = self.resolve_vars_if_possible(fn_sig);
for idx in 0..=1 {
let arg_ty = fn_sig.inputs()[idx + 1];
let span = arg_exprs.get(idx + 1).map_or(call_expr.span, |arg| arg.span);
// Check that second and third argument of `const_eval_select` must be `FnDef`, and additionally that
// the second argument must be `const fn`. The first argument must be a tuple, but this is already expressed
// in the function signature (`F: FnOnce<ARG>`), so I did not bother to add another check here.
//
// This check is here because there is currently no way to express a trait bound for `FnDef` types only.
if let ty::FnDef(def_id, _args) = *arg_ty.kind() {
let fn_once_def_id =
self.tcx.require_lang_item(hir::LangItem::FnOnce, Some(span));
let fn_once_output_def_id =
self.tcx.require_lang_item(hir::LangItem::FnOnceOutput, Some(span));
if self.tcx.generics_of(fn_once_def_id).host_effect_index.is_none() {
if idx == 0 && !self.tcx.is_const_fn_raw(def_id) {
self.tcx.sess.emit_err(errors::ConstSelectMustBeConst { span });
}
} else {
let const_param: ty::GenericArg<'tcx> =
([self.tcx.consts.false_, self.tcx.consts.true_])[idx].into();
self.register_predicate(traits::Obligation::new(
self.tcx,
self.misc(span),
self.param_env,
ty::TraitRef::new(
self.tcx,
fn_once_def_id,
[arg_ty.into(), fn_sig.inputs()[0].into(), const_param],
),
));

self.register_predicate(traits::Obligation::new(
self.tcx,
self.misc(span),
self.param_env,
ty::ProjectionPredicate {
projection_ty: ty::AliasTy::new(
self.tcx,
fn_once_output_def_id,
[arg_ty.into(), fn_sig.inputs()[0].into(), const_param],
),
term: fn_sig.output().into(),
},
));

self.select_obligations_where_possible(|_| {});
}
} else {
self.tcx.sess.emit_err(errors::ConstSelectMustBeFn { span, ty: arg_ty });
}
}
}

fn_sig.output()
}

Expand Down
29 changes: 0 additions & 29 deletions compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -230,11 +230,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
let minimum_input_count = expected_input_tys.len();
let provided_arg_count = provided_args.len();

let is_const_eval_select = matches!(fn_def_id, Some(def_id) if
self.tcx.def_kind(def_id) == hir::def::DefKind::Fn
&& self.tcx.is_intrinsic(def_id)
&& self.tcx.item_name(def_id) == sym::const_eval_select);

// We introduce a helper function to demand that a given argument satisfy a given input
// This is more complicated than just checking type equality, as arguments could be coerced
// This version writes those types back so further type checking uses the narrowed types
Expand Down Expand Up @@ -269,30 +264,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
return Compatibility::Incompatible(coerce_error);
}

// Check that second and third argument of `const_eval_select` must be `FnDef`, and additionally that
// the second argument must be `const fn`. The first argument must be a tuple, but this is already expressed
// in the function signature (`F: FnOnce<ARG>`), so I did not bother to add another check here.
//
// This check is here because there is currently no way to express a trait bound for `FnDef` types only.
if is_const_eval_select && (1..=2).contains(&idx) {
if let ty::FnDef(def_id, args) = *checked_ty.kind() {
if idx == 1 {
if !self.tcx.is_const_fn_raw(def_id) {
self.tcx.sess.emit_err(errors::ConstSelectMustBeConst {
span: provided_arg.span,
});
} else {
self.enforce_context_effects(provided_arg.span, def_id, args)
}
}
} else {
self.tcx.sess.emit_err(errors::ConstSelectMustBeFn {
span: provided_arg.span,
ty: checked_ty,
});
}
}

// 3. Check if the formal type is a supertype of the checked one
// and register any such obligations for future type checks
let supertype_error = self.at(&self.misc(provided_arg.span), self.param_env).sup(
Expand Down
32 changes: 16 additions & 16 deletions tests/ui/intrinsics/const-eval-select-bad.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -16,20 +16,24 @@ LL | const_eval_select((), || {}, || {});
= note: expected a function item, found {closure@$DIR/const-eval-select-bad.rs:7:34: 7:36}
= help: consult the documentation on `const_eval_select` for more information

error: this argument must be a function item
error[E0277]: expected a `FnOnce()` closure, found `{integer}`
--> $DIR/const-eval-select-bad.rs:10:27
|
LL | const_eval_select((), 42, 0xDEADBEEF);
| ^^
| ----------------- ^^ expected an `FnOnce()` closure, found `{integer}`
| |
| required by a bound introduced by this call
|
= note: expected a function item, found {integer}
= help: consult the documentation on `const_eval_select` for more information
= help: the trait `FnOnce<()>` is not implemented for `{integer}`
= note: wrap the `{integer}` in a closure with no arguments: `|| { /* code */ }`
note: required by a bound in `const_eval_select`
--> $SRC_DIR/core/src/intrinsics.rs:LL:COL

error[E0277]: expected a `FnOnce()` closure, found `{integer}`
--> $DIR/const-eval-select-bad.rs:10:27
--> $DIR/const-eval-select-bad.rs:10:31
|
LL | const_eval_select((), 42, 0xDEADBEEF);
| ----------------- ^^ expected an `FnOnce()` closure, found `{integer}`
| ----------------- ^^^^^^^^^^ expected an `FnOnce()` closure, found `{integer}`
| |
| required by a bound introduced by this call
|
Expand All @@ -39,26 +43,22 @@ note: required by a bound in `const_eval_select`
--> $SRC_DIR/core/src/intrinsics.rs:LL:COL

error: this argument must be a function item
--> $DIR/const-eval-select-bad.rs:10:31
--> $DIR/const-eval-select-bad.rs:10:27
|
LL | const_eval_select((), 42, 0xDEADBEEF);
| ^^^^^^^^^^
| ^^
|
= note: expected a function item, found {integer}
= help: consult the documentation on `const_eval_select` for more information

error[E0277]: expected a `FnOnce()` closure, found `{integer}`
error: this argument must be a function item
--> $DIR/const-eval-select-bad.rs:10:31
|
LL | const_eval_select((), 42, 0xDEADBEEF);
| ----------------- ^^^^^^^^^^ expected an `FnOnce()` closure, found `{integer}`
| |
| required by a bound introduced by this call
| ^^^^^^^^^^
|
= help: the trait `FnOnce<()>` is not implemented for `{integer}`
= note: wrap the `{integer}` in a closure with no arguments: `|| { /* code */ }`
note: required by a bound in `const_eval_select`
--> $SRC_DIR/core/src/intrinsics.rs:LL:COL
= note: expected a function item, found {integer}
= help: consult the documentation on `const_eval_select` for more information

error[E0271]: expected `bar` to be a fn item that returns `i32`, but it returns `bool`
--> $DIR/const-eval-select-bad.rs:32:34
Expand Down
7 changes: 6 additions & 1 deletion tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -518,5 +518,10 @@ extern "rust-intrinsic" {
arg: ARG,
called_in_const: F,
called_at_rt: G,
) -> RET;
) -> RET
/* where clauses enforced by built-in method confirmation:
where
F: const FnOnce<Arg, Output = RET>,
G: FnOnce<Arg, Output = RET>,
*/;
}

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