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Fix const-fn check in const_eval #118004

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Fix const-fn check in const_eval #118004

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19 changes: 18 additions & 1 deletion compiler/rustc_const_eval/src/transform/check_consts/check.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,9 +9,11 @@ use rustc_infer::traits::{ImplSource, Obligation, ObligationCause};
use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::traits::BuiltinImplSource;
use rustc_middle::ty::FnDef;
use rustc_middle::ty::GenericArgs;
use rustc_middle::ty::{self, adjustment::PointerCoercion, Instance, InstanceDef, Ty, TyCtxt};
use rustc_middle::ty::{TraitRef, TypeVisitableExt};
use rustc_middle::util::call_kind;
use rustc_mir_dataflow::{self, Analysis};
use rustc_span::{sym, Span, Symbol};
use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
Expand Down Expand Up @@ -846,6 +848,22 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
{
nonconst_call_permission = true;
}
let call_kind = call_kind(
tcx,
self.param_env,
callee,
fn_args,
*fn_span,
call_source.from_hir_call(),
None,
);
if let call_kind::CallKind::FnCall { fn_trait_id: _, self_ty } =
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You could use let-chains here :)

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made it more readable now

call_kind
&& let FnDef(def_id, ..) = self_ty.kind()
&& tcx.is_const_fn_raw(*def_id)
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is_const_fn_raw only checks whether the function is const, and not whether it is const-stable. We'd need a test to check whether this would silently allow calling functions that are not const-stable.

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how do we do that kind of check ?

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I'm not sure if other parts of the const checking code already check for const stability, so the first step would be creating an auxiliary ui test where upstream has a const-unstable function and downstream tries to call that function without the feature enabled (following the snippet for this ICE). If it already passes, then great. If it doesn't, we can change this from is_const_fn_raw to is_const_fn

{
return;
}

if !nonconst_call_permission {
let obligation = Obligation::new(
Expand All @@ -865,7 +883,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
&e,
);
}

self.check_op(ops::FnCallNonConst {
caller,
callee,
Expand Down
11 changes: 11 additions & 0 deletions tests/ui/consts/const-eval/const-fn-slice.rs
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@@ -0,0 +1,11 @@
//check-pass

#![feature(const_trait_impl)]
#![feature(fn_traits)]
const fn f() -> usize {
5
}

const fn main() {
let _ = [0; Fn::call(&f, ())];
}
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