Rollup merge of rust-lang#95876 - fee1-dead:note-const-drop, r=oli-obk

Add a note for unsatisfied `~const Drop` bounds

r? ```@oli-obk```

Author: matthiaskrgr

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -440,6 +440,13 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             }
                         }
 
+                        if Some(trait_ref.def_id()) == tcx.lang_items().drop_trait()
+                            && predicate_is_const
+                        {
+                            err.note("`~const Drop` was renamed to `~const Destruct`");
+                            err.note("See <https://github.com/rust-lang/rust/pull/94901> for more details");
+                        }
+
                         let explanation = if let ObligationCauseCode::MainFunctionType =
                             obligation.cause.code()
                         {

src/librustdoc/clean/mod.rs

@@ -302,23 +302,13 @@ impl<'a> Clean<Option<WherePredicate>> for ty::Predicate<'a> {
 
 impl<'a> Clean<Option<WherePredicate>> for ty::PolyTraitPredicate<'a> {
     fn clean(&self, cx: &mut DocContext<'_>) -> Option<WherePredicate> {
-        // `T: ~const Drop` is not equivalent to `T: Drop`, and we don't currently document `~const` bounds
-        // because of its experimental status, so just don't show these.
         // `T: ~const Destruct` is hidden because `T: Destruct` is a no-op.
         if self.skip_binder().constness == ty::BoundConstness::ConstIfConst
-            && [cx.tcx.lang_items().drop_trait(), cx.tcx.lang_items().destruct_trait()]
-                .iter()
-                .any(|tr| *tr == Some(self.skip_binder().def_id()))
+            && Some(self.skip_binder().def_id()) == cx.tcx.lang_items().destruct_trait()
         {
             return None;
         }
 
-        #[cfg(bootstrap)]
-        {
-            // FIXME: remove `lang_items().drop_trait()` from above logic,
-            // as well as the comment about `~const Drop` because it was renamed to `Destruct`.
-        }
-
         let poly_trait_ref = self.map_bound(|pred| pred.trait_ref);
         Some(WherePredicate::BoundPredicate {
             ty: poly_trait_ref.skip_binder().self_ty().clean(cx),

src/test/rustdoc/rfc-2632-const-trait-impl.rs

@@ -1,5 +1,5 @@
 // Test that we do not currently display `~const` in rustdoc
-// as that syntax is currently provisional; `~const Drop` has
+// as that syntax is currently provisional; `~const Destruct` has
 // no effect on stable code so it should be hidden as well.
 //
 // To future blessers: make sure that `const_trait_impl` is
@@ -8,6 +8,8 @@
 #![feature(const_trait_impl)]
 #![crate_name = "foo"]
 
+use std::marker::Destruct;
+
 pub struct S<T>(T);
 
 // @!has foo/trait.Tr.html '//pre[@class="rust trait"]/code/a[@class="trait"]' '~const'
@@ -20,22 +22,36 @@ pub trait Tr<T> {
     // @!has - '//div[@id="method.a"]/h4[@class="code-header"]/span[@class="where"]' '~const'
     // @has - '//div[@id="method.a"]/h4[@class="code-header"]/span[@class="where fmt-newline"]' ': Clone'
     #[default_method_body_is_const]
-    fn a<A: ~const Clone>() where Option<A>: ~const Clone {}
+    fn a<A: ~const Clone + ~const Destruct>()
+    where
+        Option<A>: ~const Clone + ~const Destruct,
+    {
+    }
 }
 
 // @!has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]' '~const'
 // @has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]/a[@class="trait"]' 'Clone'
 // @!has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]/span[@class="where"]' '~const'
 // @has - '//section[@id="impl-Tr%3CT%3E"]/h3[@class="code-header in-band"]/span[@class="where fmt-newline"]' ': Clone'
-impl<T: ~const Clone> const Tr<T> for T where Option<T>: ~const Clone {
-    fn a<A: ~const Clone>() where Option<A>: ~const Clone {}
+impl<T: ~const Clone + ~const Destruct> const Tr<T> for T
+where
+    Option<T>: ~const Clone + ~const Destruct,
+{
+    fn a<A: ~const Clone + ~const Destruct>()
+    where
+        Option<A>: ~const Clone + ~const Destruct,
+    {
+    }
 }
 
 // @!has foo/fn.foo.html '//pre[@class="rust fn"]/code/a[@class="trait"]' '~const'
 // @has - '//pre[@class="rust fn"]/code/a[@class="trait"]' 'Clone'
 // @!has - '//pre[@class="rust fn"]/code/span[@class="where fmt-newline"]' '~const'
 // @has - '//pre[@class="rust fn"]/code/span[@class="where fmt-newline"]' ': Clone'
-pub const fn foo<F: ~const Clone>() where Option<F>: ~const Clone {
+pub const fn foo<F: ~const Clone + ~const Destruct>()
+where
+    Option<F>: ~const Clone + ~const Destruct,
+{
     F::a()
 }
 
@@ -44,7 +60,10 @@ impl<T> S<T> {
     // @has - '//section[@id="method.foo"]/h4[@class="code-header"]/a[@class="trait"]' 'Clone'
     // @!has - '//section[@id="method.foo"]/h4[@class="code-header"]/span[@class="where"]' '~const'
     // @has - '//section[@id="method.foo"]/h4[@class="code-header"]/span[@class="where fmt-newline"]' ': Clone'
-    pub const fn foo<B: ~const Clone>() where B: ~const Clone {
+    pub const fn foo<B: ~const Clone + ~const Destruct>()
+    where
+        B: ~const Clone + ~const Destruct,
+    {
         B::a()
     }
 }