Auto merge of #118689 - compiler-errors:const-drop, r=fee1-dead

Fix const drop checking

Fixes confirmation of `~const Destruct` and const drops.

r? fee1-dead

3 files changed, 30 insertions, 20 deletions

diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index bcc42a376ea..e604f4c1aec 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -22,7 +22,7 @@ use std::mem;
 use std::ops::{ControlFlow, Deref};
 
 use super::ops::{self, NonConstOp, Status};
-use super::qualifs::{self, CustomEq, HasMutInterior, NeedsDrop};
+use super::qualifs::{self, CustomEq, HasMutInterior, NeedsDrop, NeedsNonConstDrop};
 use super::resolver::FlowSensitiveAnalysis;
 use super::{ConstCx, Qualif};
 use crate::const_eval::is_unstable_const_fn;
@@ -35,7 +35,7 @@ type QualifResults<'mir, 'tcx, Q> =
 pub struct Qualifs<'mir, 'tcx> {
     has_mut_interior: Option<QualifResults<'mir, 'tcx, HasMutInterior>>,
     needs_drop: Option<QualifResults<'mir, 'tcx, NeedsDrop>>,
-    // needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>,
+    needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>,
 }
 
 impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
@@ -78,27 +78,25 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
         local: Local,
         location: Location,
     ) -> bool {
-        // FIXME(effects) replace with `NeedsNonconstDrop` after const traits work again
-        /*
         let ty = ccx.body.local_decls[local].ty;
-        if !NeedsDrop::in_any_value_of_ty(ccx, ty) {
+        // Peeking into opaque types causes cycles if the current function declares said opaque
+        // type. Thus we avoid short circuiting on the type and instead run the more expensive
+        // analysis that looks at the actual usage within this function
+        if !ty.has_opaque_types() && !NeedsNonConstDrop::in_any_value_of_ty(ccx, ty) {
             return false;
         }
 
         let needs_non_const_drop = self.needs_non_const_drop.get_or_insert_with(|| {
             let ConstCx { tcx, body, .. } = *ccx;
 
-            FlowSensitiveAnalysis::new(NeedsDrop, ccx)
-                .into_engine(tcx, &body)
+            FlowSensitiveAnalysis::new(NeedsNonConstDrop, ccx)
+                .into_engine(tcx, body)
                 .iterate_to_fixpoint()
-                .into_results_cursor(&body)
+                .into_results_cursor(body)
         });
 
         needs_non_const_drop.seek_before_primary_effect(location);
         needs_non_const_drop.get().contains(local)
-        */
-
-        self.needs_drop(ccx, local, location)
     }
 
     /// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
@@ -1013,9 +1011,8 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 let mut err_span = self.span;
                 let ty_of_dropped_place = dropped_place.ty(self.body, self.tcx).ty;
 
-                // FIXME(effects) replace with `NeedsNonConstDrop` once we fix const traits
                 let ty_needs_non_const_drop =
-                    qualifs::NeedsDrop::in_any_value_of_ty(self.ccx, ty_of_dropped_place);
+                    qualifs::NeedsNonConstDrop::in_any_value_of_ty(self.ccx, ty_of_dropped_place);
 
                 debug!(?ty_of_dropped_place, ?ty_needs_non_const_drop);
 
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs b/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs
index 06371438ec1..5cd13783c23 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs
@@ -5,7 +5,7 @@ use rustc_span::{symbol::sym, Span};
 
 use super::check::Qualifs;
 use super::ops::{self, NonConstOp};
-use super::qualifs::{NeedsDrop, Qualif};
+use super::qualifs::{NeedsNonConstDrop, Qualif};
 use super::ConstCx;
 
 /// Returns `true` if we should use the more precise live drop checker that runs after drop
@@ -83,8 +83,7 @@ impl<'tcx> Visitor<'tcx> for CheckLiveDrops<'_, 'tcx> {
             mir::TerminatorKind::Drop { place: dropped_place, .. } => {
                 let dropped_ty = dropped_place.ty(self.body, self.tcx).ty;
 
-                // FIXME(effects) use `NeedsNonConstDrop`
-                if !NeedsDrop::in_any_value_of_ty(self.ccx, dropped_ty) {
+                if !NeedsNonConstDrop::in_any_value_of_ty(self.ccx, dropped_ty) {
                     // Instead of throwing a bug, we just return here. This is because we have to
                     // run custom `const Drop` impls.
                     return;
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
index de3186a53c1..d5f418e1710 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
@@ -23,8 +23,7 @@ pub fn in_any_value_of_ty<'tcx>(
     ConstQualifs {
         has_mut_interior: HasMutInterior::in_any_value_of_ty(cx, ty),
         needs_drop: NeedsDrop::in_any_value_of_ty(cx, ty),
-        // FIXME(effects)
-        needs_non_const_drop: NeedsDrop::in_any_value_of_ty(cx, ty),
+        needs_non_const_drop: NeedsNonConstDrop::in_any_value_of_ty(cx, ty),
         custom_eq: CustomEq::in_any_value_of_ty(cx, ty),
         tainted_by_errors,
     }
@@ -155,12 +154,27 @@ impl Qualif for NeedsNonConstDrop {
             return false;
         }
 
-        // FIXME(effects) constness
+        // FIXME(effects): If `destruct` is not a `const_trait`,
+        // or effects are disabled in this crate, then give up.
+        let destruct_def_id = cx.tcx.require_lang_item(LangItem::Destruct, Some(cx.body.span));
+        if cx.tcx.generics_of(destruct_def_id).host_effect_index.is_none()
+            || !cx.tcx.features().effects
+        {
+            return NeedsDrop::in_any_value_of_ty(cx, ty);
+        }
+
         let obligation = Obligation::new(
             cx.tcx,
             ObligationCause::dummy_with_span(cx.body.span),
             cx.param_env,
-            ty::TraitRef::from_lang_item(cx.tcx, LangItem::Destruct, cx.body.span, [ty]),
+            ty::TraitRef::new(
+                cx.tcx,
+                destruct_def_id,
+                [
+                    ty::GenericArg::from(ty),
+                    ty::GenericArg::from(cx.tcx.expected_const_effect_param_for_body(cx.def_id())),
+                ],
+            ),
         );
 
         let infcx = cx.tcx.infer_ctxt().build();