Check drop is trivial before checking ty needs drop

Author: compiler-errors

compiler/rustc_const_eval/src/check_consts/qualifs.rs

@@ -175,6 +175,11 @@ impl Qualif for NeedsNonConstDrop {
             return false;
         }
 
+        // If this doesn't need drop at all, then don't select `~const Destruct`.
+        if !ty.needs_drop(cx.tcx, cx.typing_env) {
+            return false;
+        }
+
         // We check that the type is `~const Destruct` since that will verify that
         // the type is both `~const Drop` (if a drop impl exists for the adt), *and*
         // that the components of this type are also `~const Destruct`. This
@@ -203,7 +208,7 @@ impl Qualif for NeedsNonConstDrop {
         // in its value since:
         // 1. The destructor may have `~const` bounds which are not present on the type.
         //   Someone needs to check that those are satisfied.
-        //   While this could be done instead satisfied by checking that the `~const Drop`
+        //   While this could be instead satisfied by checking that the `~const Drop`
         //   impl holds (i.e. replicating part of the `in_any_value_of_ty` logic above),
         //   even in this case, we have another problem, which is,
         // 2. The destructor may *modify* the operand being dropped, so even if we

compiler/rustc_feature/src/unstable.rs

@@ -426,7 +426,7 @@ declare_features! (
     (unstable, const_async_blocks, "1.53.0", Some(85368)),
     /// Allows `const || {}` closures in const contexts.
     (incomplete, const_closures, "1.68.0", Some(106003)),
-    /// Uwu
+    /// Allows using `~const Destruct` bounds and calling drop impls in const contexts.
     (unstable, const_destruct, "CURRENT_RUSTC_VERSION", Some(133214)),
     /// Allows `for _ in _` loops in const contexts.
     (unstable, const_for, "1.56.0", Some(87575)),

compiler/rustc_middle/src/ty/context.rs

@@ -4,7 +4,7 @@
 
 pub mod tls;
 
-use std::assert_matches::assert_matches;
+use std::assert_matches::{assert_matches, debug_assert_matches};
 use std::borrow::Borrow;
 use std::cmp::Ordering;
 use std::hash::{Hash, Hasher};
@@ -377,14 +377,17 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     }
 
     fn impl_is_const(self, def_id: DefId) -> bool {
+        debug_assert_matches!(self.def_kind(def_id), DefKind::Impl { of_trait: true });
         self.is_conditionally_const(def_id)
     }
 
     fn fn_is_const(self, def_id: DefId) -> bool {
+        debug_assert_matches!(self.def_kind(def_id), DefKind::Fn | DefKind::AssocFn);
         self.is_conditionally_const(def_id)
     }
 
     fn alias_has_const_conditions(self, def_id: DefId) -> bool {
+        debug_assert_matches!(self.def_kind(def_id), DefKind::AssocTy | DefKind::OpaqueTy);
         self.is_conditionally_const(def_id)
     }
 

tests/ui/consts/const-block-const-bound.rs

@@ -1,7 +1,7 @@
 //@ known-bug: #103507
 
 #![allow(unused)]
-#![feature(const_trait_impl, negative_impls)]
+#![feature(const_trait_impl, negative_impls, const_destruct)]
 
 use std::marker::Destruct;
 

tests/ui/consts/const-block-const-bound.stderr

@@ -1,23 +1,3 @@
-error[E0658]: use of unstable library feature `const_destruct`
-  --> $DIR/const-block-const-bound.rs:6:5
-   |
-LL | use std::marker::Destruct;
-   |     ^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #133214 <https://github.com/rust-lang/rust/issues/133214> for more information
-   = help: add `#![feature(const_destruct)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error[E0658]: use of unstable library feature `const_destruct`
-  --> $DIR/const-block-const-bound.rs:8:22
-   |
-LL | const fn f<T: ~const Destruct>(x: T) {}
-   |                      ^^^^^^^^
-   |
-   = note: see issue #133214 <https://github.com/rust-lang/rust/issues/133214> for more information
-   = help: add `#![feature(const_destruct)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
 error: `~const` can only be applied to `#[const_trait]` traits
   --> $DIR/const-block-const-bound.rs:8:15
    |
@@ -40,7 +20,6 @@ LL | const fn f<T: ~const Destruct>(x: T) {}
    |                                |
    |                                the destructor for this type cannot be evaluated in constant functions
 
-error: aborting due to 5 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0493, E0658.
-For more information about an error, try `rustc --explain E0493`.
+For more information about this error, try `rustc --explain E0493`.

tests/ui/consts/fn_trait_refs.rs

@@ -5,6 +5,7 @@
 #![feature(unboxed_closures)]
 #![feature(const_trait_impl)]
 #![feature(const_cmp)]
+#![feature(const_destruct)]
 
 use std::marker::Destruct;