allow+update `deref_into_dyn_supertrait`

this commit makes `deref_into_dyn_supertrait` lint allow-by-default,
removes future incompatibility (we finally live in a broken world), and
changes the wording in the documentation.

previously documentation erroneously said that it lints against *usage*
of the deref impl, while it actually (since 104742) lints on the impl
itself (oooops, my oversight, should have updated it 2+ years ago...)

1 files changed, 11 insertions, 13 deletions

diff --git a/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs b/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs
index 07f46aba05b..181f44fb4de 100644
--- a/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs
+++ b/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs
@@ -1,6 +1,5 @@
 use rustc_hir::{self as hir, LangItem};
 use rustc_middle::ty;
-use rustc_session::lint::FutureIncompatibilityReason;
 use rustc_session::{declare_lint, declare_lint_pass};
 use rustc_span::sym;
 use rustc_trait_selection::traits::supertraits;
@@ -9,12 +8,12 @@ use crate::lints::{SupertraitAsDerefTarget, SupertraitAsDerefTargetLabel};
 use crate::{LateContext, LateLintPass, LintContext};
 
 declare_lint! {
-    /// The `deref_into_dyn_supertrait` lint is output whenever there is a use of the
-    /// `Deref` implementation with a `dyn SuperTrait` type as `Output`.
+    /// The `deref_into_dyn_supertrait` lint is emitted whenever there is a `Deref` implementation
+    /// for `dyn SubTrait` with a `dyn SuperTrait` type as the `Output` type.
     ///
-    /// These implementations are shadowed by the `trait_upcasting` feature (stabilized since
+    /// These implementations are "shadowed" by trait upcasting (stabilized since
     /// CURRENT_RUSTC_VERSION). The `deref` functions is no longer called implicitly, which might
-    /// be behavior change compared to previous rustc versions.
+    /// change behavior compared to previous rustc versions.
     ///
     /// ### Example
     ///
@@ -44,15 +43,14 @@ declare_lint! {
     ///
     /// ### Explanation
     ///
-    /// The dyn upcasting coercion feature added a new coercion rules, taking priority
-    /// over certain other coercion rules, which caused some behavior change.
+    /// The trait upcasting coercion added a new coercion rule, taking priority over certain other
+    /// coercion rules, which causes some behavior change compared to older `rustc` versions.
+    ///
+    /// `deref` can be still called explicitly, it just isn't called as part of a deref coercion
+    /// (since trait upcasting coercion takes priority).
     pub DEREF_INTO_DYN_SUPERTRAIT,
-    Warn,
-    "`Deref` implementation usage with a supertrait trait object for output is shadowed by trait upcasting",
-    @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
-        reference: "issue #89460 <https://github.com/rust-lang/rust/issues/89460>",
-    };
+    Allow,
+    "`Deref` implementation with a supertrait trait object for output is shadowed by trait upcasting",
 }
 
 declare_lint_pass!(DerefIntoDynSupertrait => [DEREF_INTO_DYN_SUPERTRAIT]);