1 files changed, 87 insertions, 4 deletions
diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 9561b3de5f8..97850a2afc1 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -101,6 +101,8 @@ declare_lint_pass! {
         SINGLE_USE_LIFETIMES,
         SOFT_UNSTABLE,
         STABLE_FEATURES,
+        SUPERTRAIT_ITEM_SHADOWING_DEFINITION,
+        SUPERTRAIT_ITEM_SHADOWING_USAGE,
         TAIL_EXPR_DROP_ORDER,
         TEST_UNSTABLE_LINT,
         TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
@@ -2778,7 +2780,7 @@ declare_lint! {
     ///
     /// ```rust
     /// enum Void {}
-    /// extern {
+    /// unsafe extern {
     ///     static EXTERN: Void;
     /// }
     /// ```
@@ -4009,7 +4011,7 @@ declare_lint! {
     /// ```rust
     /// #![warn(ffi_unwind_calls)]
     ///
-    /// extern "C-unwind" {
+    /// unsafe extern "C-unwind" {
     ///     fn foo();
     /// }
     ///
@@ -4753,7 +4755,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust
+    /// ```rust,edition2021
     /// #![warn(missing_unsafe_on_extern)]
     /// #![allow(dead_code)]
     ///
@@ -4790,7 +4792,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust
+    /// ```rust,edition2021
     /// #![warn(unsafe_attr_outside_unsafe)]
     ///
     /// #[no_mangle]
@@ -4917,6 +4919,87 @@ declare_lint! {
 }
 
 declare_lint! {
+    /// The `supertrait_item_shadowing_usage` lint detects when the
+    /// usage of an item that is provided by both a subtrait and supertrait
+    /// is shadowed, preferring the subtrait.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![feature(supertrait_item_shadowing)]
+    /// #![deny(supertrait_item_shadowing_usage)]
+    ///
+    /// trait Upstream {
+    ///     fn hello(&self) {}
+    /// }
+    /// impl<T> Upstream for T {}
+    ///
+    /// trait Downstream: Upstream {
+    ///     fn hello(&self) {}
+    /// }
+    /// impl<T> Downstream for T {}
+    ///
+    /// struct MyType;
+    /// MyType.hello();
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// RFC 3624 specified a heuristic in which a supertrait item would be
+    /// shadowed by a subtrait item when ambiguity occurs during item
+    /// selection. In order to mitigate side-effects of this happening
+    /// silently, this lint detects these cases when users want to deny them
+    /// or fix the call sites.
+    pub SUPERTRAIT_ITEM_SHADOWING_USAGE,
+    // FIXME(supertrait_item_shadowing): It is not decided if this should
+    // warn by default at the call site.
+    Allow,
+    "detects when a supertrait item is shadowed by a subtrait item",
+    @feature_gate = supertrait_item_shadowing;
+}
+
+declare_lint! {
+    /// The `supertrait_item_shadowing_definition` lint detects when the
+    /// definition of an item that is provided by both a subtrait and
+    /// supertrait is shadowed, preferring the subtrait.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![feature(supertrait_item_shadowing)]
+    /// #![deny(supertrait_item_shadowing_definition)]
+    ///
+    /// trait Upstream {
+    ///     fn hello(&self) {}
+    /// }
+    /// impl<T> Upstream for T {}
+    ///
+    /// trait Downstream: Upstream {
+    ///     fn hello(&self) {}
+    /// }
+    /// impl<T> Downstream for T {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// RFC 3624 specified a heuristic in which a supertrait item would be
+    /// shadowed by a subtrait item when ambiguity occurs during item
+    /// selection. In order to mitigate side-effects of this happening
+    /// silently, this lint detects these cases when users want to deny them
+    /// or fix their trait definitions.
+    pub SUPERTRAIT_ITEM_SHADOWING_DEFINITION,
+    // FIXME(supertrait_item_shadowing): It is not decided if this should
+    // warn by default at the usage site.
+    Allow,
+    "detects when a supertrait item is shadowed by a subtrait item",
+    @feature_gate = supertrait_item_shadowing;
+}
+
+declare_lint! {
     /// The `ptr_to_integer_transmute_in_consts` lint detects pointer to integer
     /// transmute in const functions and associated constants.
     ///