diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
index 39402cfc35dce..32678e8a5a12f 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
@@ -409,9 +409,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
     pub(super) fn report_ambiguous_assoc_item(
         &self,
-        bound1: ty::PolyTraitRef<'tcx>,
-        bound2: ty::PolyTraitRef<'tcx>,
-        matching_candidates: impl Iterator<Item = ty::PolyTraitRef<'tcx>>,
+        matching_candidates: &[ty::PolyTraitRef<'tcx>],
         qself: AssocItemQSelf,
         assoc_tag: ty::AssocTag,
         assoc_ident: Ident,
@@ -443,7 +441,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         // predicates!).
         // FIXME: Turn this into a structured, translatable & more actionable suggestion.
         let mut where_bounds = vec![];
-        for bound in [bound1, bound2].into_iter().chain(matching_candidates) {
+        for &bound in matching_candidates {
             let bound_id = bound.def_id();
             let assoc_item = tcx.associated_items(bound_id).find_by_ident_and_kind(
                 tcx,
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index baa9fddc2a651..2d0dab03f2c46 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -24,6 +24,7 @@ use std::{assert_matches, slice};
 use rustc_abi::FIRST_VARIANT;
 use rustc_ast::LitKind;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
+use rustc_data_structures::sso::SsoHashSet;
 use rustc_errors::codes::*;
 use rustc_errors::{
     Applicability, Diag, DiagCtxtHandle, ErrorGuaranteed, FatalError, StashKey,
@@ -1262,6 +1263,74 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         )
     }
 
+    /// When there are multiple traits which contain an identically named
+    /// associated item, this function eliminates any traits which are a
+    /// supertrait of another candidate trait.
+    ///
+    /// This is the type-level analogue of
+    /// `rustc_hir_typeck::method::probe::ProbeContext::collapse_candidates_to_subtrait_pick`;
+    /// keep both implementations in sync.
+    ///
+    /// This implements RFC #3624.
+    fn collapse_candidates_to_subtrait_pick(
+        &self,
+        matching_candidates: &[ty::PolyTraitRef<'tcx>],
+    ) -> Option<ty::PolyTraitRef<'tcx>> {
+        if !self.tcx().features().supertrait_item_shadowing() {
+            return None;
+        }
+
+        let mut child_trait = matching_candidates[0];
+        let mut supertraits: SsoHashSet<_> =
+            traits::supertrait_def_ids(self.tcx(), child_trait.def_id()).collect();
+
+        let mut remaining_candidates: Vec<_> = matching_candidates[1..].iter().copied().collect();
+        while !remaining_candidates.is_empty() {
+            let mut made_progress = false;
+            let mut next_round = vec![];
+
+            for remaining_trait in remaining_candidates {
+                if supertraits.contains(&remaining_trait.def_id()) {
+                    made_progress = true;
+                    continue;
+                }
+
+                // This candidate is not a supertrait of the `child_trait`.
+                // Check if it's a subtrait of the `child_trait`, instead.
+                // If it is, then it must have been a subtrait of every
+                // other pick we've eliminated at this point. It will
+                // take over at this point.
+                let remaining_trait_supertraits: SsoHashSet<_> =
+                    traits::supertrait_def_ids(self.tcx(), remaining_trait.def_id()).collect();
+                if remaining_trait_supertraits.contains(&child_trait.def_id()) {
+                    child_trait = remaining_trait;
+                    supertraits = remaining_trait_supertraits;
+                    made_progress = true;
+                    continue;
+                }
+
+                // Neither `child_trait` or the current candidate are
+                // supertraits of each other.
+                // Don't bail here, since we may be comparing two supertraits
+                // of a common subtrait. These two supertraits won't be related
+                // at all, but we will pick them up next round when we find their
+                // child as we continue iterating in this round.
+                next_round.push(remaining_trait);
+            }
+
+            if made_progress {
+                // If we've made progress, iterate again.
+                remaining_candidates = next_round;
+            } else {
+                // Otherwise, we must have at least two candidates which
+                // are not related to each other at all.
+                return None;
+            }
+        }
+
+        Some(child_trait)
+    }
+
     /// Search for a single trait bound whose trait defines the associated item given by
     /// `assoc_ident`.
     ///
@@ -1296,10 +1365,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         };
 
         if let Some(bound2) = matching_candidates.next() {
+            let all_matching_candidates: Vec<_> =
+                [bound1, bound2].into_iter().chain(matching_candidates).collect();
+            if let Some(bound) = self.collapse_candidates_to_subtrait_pick(&all_matching_candidates)
+            {
+                return Ok(bound);
+            }
+
             return Err(self.report_ambiguous_assoc_item(
-                bound1,
-                bound2,
-                matching_candidates,
+                &all_matching_candidates,
                 qself,
                 assoc_tag,
                 assoc_ident,
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index e8921841c4405..ce187aa1aff14 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -2359,6 +2359,10 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     /// multiple conflicting picks if there is one pick whose trait container is a subtrait
     /// of the trait containers of all of the other picks.
     ///
+    /// This is the method-probe analogue of
+    /// `rustc_hir_analysis::hir_ty_lowering::HirTyLowerer::collapse_candidates_to_subtrait_pick`;
+    /// keep both implementations in sync.
+    ///
     /// This implements RFC #3624.
     fn collapse_candidates_to_subtrait_pick(
         &self,
diff --git a/library/std/src/attribute_docs.rs b/library/std/src/attribute_docs.rs
index 1d8dddb7ca54a..e8d36483f3139 100644
--- a/library/std/src/attribute_docs.rs
+++ b/library/std/src/attribute_docs.rs
@@ -85,3 +85,253 @@
 /// [`unused_must_use`]: ../rustc/lints/listing/warn-by-default.html#unused-must-use
 /// [the `must_use` attribute]: ../reference/attributes/diagnostics.html#the-must_use-attribute
 mod must_use_attribute {}
+
+#[doc(attribute = "allow")]
+//
+/// The `allow` attribute suppresses lint diagnostics that would otherwise produce
+/// warnings or errors. It can be used on any lint or lint group (except those
+/// set to `forbid`).
+///
+/// ```rust
+/// #[allow(dead_code)]
+/// fn unused_function() {
+///     // ...
+/// }
+///
+/// fn main() {
+///   // `unused_function` does not generate a compiler warning.
+/// }
+/// ```
+///
+/// Without `#[allow(dead_code)]`, the example above would emit:
+///
+/// ```text
+/// warning: function `unused_function` is never used
+///  --> main.rs:1:4
+///   |
+/// 1 | fn unused_function() {
+///   |    ^^^^^^^^^^^^^^^
+///   |
+///   = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default
+///
+///   warning: 1 warning emitted
+/// ```
+///
+/// Multiple lints can be set to `allow` at once with commas:
+///
+/// ```rust
+/// #[allow(unused_variables, unused_mut)]
+/// fn main() {
+///     let mut x: u32 = 42;
+/// }
+/// ```
+///
+/// This is mostly used to prevent lint warnings or errors while still under development.
+///
+/// It cannot override a lint that has been set to `forbid`.
+///
+/// It's also important to consider that overusing `allow` could make code harder to maintain
+/// and possibly hide issues. To mitigate this issue, using the `expect` attribute is preferred.
+///
+/// `allow` can be overridden by `warn`, `deny`, and `forbid`.
+///
+/// The lint checks supported by rustc can be found via `rustc -W help`,
+/// along with their default settings and are documented in [the `rustc` book].
+///
+/// [the `rustc` book]: ../rustc/lints/listing/index.html
+///
+/// For more information, see the Reference on [the `allow` attribute].
+///
+/// [the `allow` attribute]: ../reference/attributes/diagnostics.html#lint-check-attributes
+mod allow_attribute {}
+
+#[doc(attribute = "cfg")]
+//
+/// Used for conditional compilation.
+///
+/// The `cfg` attribute allows compiling an item under specific conditions, otherwise it
+/// will be ignored.
+///
+/// ```rust
+/// // Only compiles this function for Linux.
+/// #[cfg(target_os = "linux")]
+/// fn platform_specific() {
+///     println!("Running on Linux");
+/// }
+///
+/// // Only compiles this function if not for Linux.
+/// #[cfg(not(target_os = "linux"))]
+/// fn platform_specific() {
+///     println!("Running on something else");
+/// }
+/// ```
+///
+/// Depending on the platform you're targeting, only one of these two functions will be considered
+/// during the compilation.
+///
+/// Conditions can also be combined with `all(...)`, `any(...)`, and `not(...)`.
+///
+/// * `all`: True if all given predicates are true.
+/// * `any`: True if at least one of the given predicates is true.
+/// * `not`: True if the predicate is false and false if the predicate is true.
+///
+/// ```rust
+/// #[cfg(all(unix, target_pointer_width = "64"))]
+/// fn unix_64bit() {
+/// }
+/// ```
+///
+/// If you want to use this mechanism in an `if` condition in your code, you
+/// can use the [`cfg!`] macro. To conditionally apply an attribute,
+/// see [`cfg_attr`].
+///
+/// For more information, see the Reference on [the `cfg` attribute].
+///
+/// [`cfg_attr`]: ../reference/conditional-compilation.html#the-cfg_attr-attribute
+/// [the `cfg` attribute]: ../reference/conditional-compilation.html#the-cfg-attribute
+mod cfg_attribute {}
+
+#[doc(attribute = "deny")]
+//
+/// Emits an error, preventing the compilation from finishing, when a lint check has failed.
+/// This is useful for enforcing rules or preventing certain patterns:
+///
+/// ```rust,compile_fail
+/// #[deny(unused)]
+/// fn foo() {
+///     let x = 42; // Emits an error because x is unused.
+/// }
+/// ```
+///
+/// `deny` can be overridden by `allow`, `warn`, and `forbid`:
+///
+/// ```rust
+/// #![deny(unused)]
+///
+/// #[allow(unused)] // We override the `deny` for this function.
+/// fn foo() {
+///     let x = 42; // No lint emitted even though `x` is unused.
+/// }
+/// ```
+///
+/// Multiple lints can also be set to `deny` at once:
+///
+/// ```rust,compile_fail
+/// #![deny(unused_imports, unused_variables)]
+/// use std::collections::*;
+///
+/// fn main() {
+///     let mut x = 10;
+/// }
+/// ```
+///
+/// The lint checks supported by rustc can be found via `rustc -W help`,
+/// along with their default settings and are documented in [the `rustc` book].
+///
+/// [the `rustc` book]: ../rustc/lints/listing/index.html
+///
+/// For more information, see the Reference on [the `deny` attribute].
+///
+/// [the `deny` attribute]: ../reference/attributes/diagnostics.html#lint-check-attributes
+mod deny_attribute {}
+
+#[doc(attribute = "forbid")]
+//
+/// Emits an error, preventing the compilation from finishing, when a lint check has failed.
+///
+/// A lint set to `forbid` cannot be overridden by `allow` or `warn`.
+/// Attempting either will result in a compilation error. Writing `#[deny(...)]` on the same lint inside a
+/// `forbid` scope is permitted, but has no effect; the lint remains at the `forbid` level.
+///
+/// This is useful for enforcing strict policies that should not be relaxed
+/// anywhere in the codebase. Example:
+///
+/// ```rust
+/// #![forbid(unsafe_code)]
+///
+/// // This would cause a compilation error if uncommented:
+/// // #[allow(unsafe_code)] // error: cannot override `forbid`
+/// ```
+///
+/// Multiple lints can be set to `forbid` at once:
+///
+/// ```rust
+/// #![forbid(unsafe_code, unused)]
+/// ```
+///
+/// The lint checks supported by rustc can be found via `rustc -W help`,
+/// along with their default settings and are documented in [the `rustc` book].
+///
+/// [the `rustc` book]: ../rustc/lints/listing/index.html
+///
+/// For more information, see the Reference on [the `forbid` attribute].
+///
+/// [the `forbid` attribute]: ../reference/attributes/diagnostics.html#lint-check-attributes
+mod forbid_attribute {}
+
+#[doc(attribute = "deprecated")]
+//
+/// Emits a warning during compilation when an item with this attribute is used.
+/// `since` and `note` are optional fields giving more detail about why the item is deprecated.
+///
+/// * `since`: the version since when the item is deprecated.
+/// * `note`: the reason why an item is deprecated.
+///
+/// Example:
+///
+/// ```rust
+/// #[deprecated(since = "1.0.0", note = "Use bar instead")]
+/// struct Foo;
+/// struct Bar;
+/// ```
+///
+/// `deprecated` attribute helps developers transition away from old code by providing warnings when
+/// deprecated items are used. Note that during `Cargo` builds, warnings on dependencies get silenced
+/// by default, so you may not see a deprecation warning unless you build that dependency directly.
+///
+/// For more information, see the Reference on [the `deprecated` attribute].
+///
+/// [the `deprecated` attribute]: ../reference/attributes/diagnostics.html#the-deprecated-attribute
+mod deprecated_attribute {}
+
+#[doc(attribute = "warn")]
+//
+/// Emits a warning during compilation when a lint check failed.
+///
+/// Unlike `deny` or `forbid`, `warn` does not produce a hard error: the compilation continues, but
+/// the compiler emits a warning message. `warn` can be overridden by `allow`, `deny`, and `forbid`.
+///
+/// Example:
+///
+/// ```rust,compile_fail
+/// #![allow(unused)]
+///
+/// #[warn(unused)] // We override the allowed `unused` lint.
+/// fn foo() {
+///     // This lint warns by default even without #[warn(unused)] being explicitly set
+///     let x = 42; // warning: unused variable `x`
+/// }
+/// ```
+///
+///
+/// Many lints, including `unused`, are already set to `warn` by default so this attribute is
+/// mainly useful for lints that are normally `allow` by default.
+///
+/// Multiple lints can be set to `warn` at once:
+///
+/// ```rust,compile_fail
+/// #[warn(unused_mut, unused_variables)]
+/// fn main() {
+///     let mut x = 42;
+/// }
+/// ```
+///
+/// The lint checks supported by rustc can be found via `rustc -W help`,
+/// along with their default settings and are documented in [the `rustc` book].
+///
+/// [the `rustc` book]: ../rustc/lints/listing/index.html
+///
+/// For more information, see the Reference on [the `warn` attribute].
+///
+/// [the `warn` attribute]: ../reference/attributes/diagnostics.html#lint-check-attributes
+mod warn_attribute {}
diff --git a/library/std/src/sys/thread/unix.rs b/library/std/src/sys/thread/unix.rs
index eb3fcff05ea9e..dd7b7940de510 100644
--- a/library/std/src/sys/thread/unix.rs
+++ b/library/std/src/sys/thread/unix.rs
@@ -392,6 +392,7 @@ pub fn current_os_id() -> Option<u64> {
     target_os = "vxworks",
     target_os = "cygwin",
     target_vendor = "apple",
+    target_os = "netbsd",
 ))]
 fn truncate_cstr<const MAX_WITH_NUL: usize>(cstr: &CStr) -> [libc::c_char; MAX_WITH_NUL] {
     let mut result = [0; MAX_WITH_NUL];
@@ -463,7 +464,12 @@ pub fn set_name(name: &CStr) {
 
 #[cfg(target_os = "netbsd")]
 pub fn set_name(name: &CStr) {
+    // See https://github.com/NetBSD/src/blob/8d40872b4c550a802379f3b9c22a40212d5e149d/lib/libpthread/pthread.h#L281
+    // FIXME: move to libc.
+    const PTHREAD_MAX_NAMELEN_NP: usize = 32;
+
     unsafe {
+        let name = truncate_cstr::<{ PTHREAD_MAX_NAMELEN_NP }>(name);
         let res = libc::pthread_setname_np(
             libc::pthread_self(),
             c"%s".as_ptr(),
diff --git a/tests/ui/README.md b/tests/ui/README.md
index 6ffef1a1cd699..d342f393d0550 100644
--- a/tests/ui/README.md
+++ b/tests/ui/README.md
@@ -1351,6 +1351,10 @@ Generic collection of tests for suggestions, when no more specific directories a
 
 **FIXME**: Some overlap with `tests/ui/did_you_mean/`, that directory should probably be moved under here.
 
+## `tests/ui/supertrait-shadowing/`
+
+Tests for supertrait item shadowing (RFC 3624).
+
 ## `tests/ui/svh/`: Strict Version Hash
 
 Tests on the *Strict Version Hash* (SVH, also known as the "crate hash").
diff --git a/tests/ui/methods/supertrait-shadowing/assoc-const.rs b/tests/ui/methods/supertrait-shadowing/assoc-const.rs
deleted file mode 100644
index 01d045b9fb74f..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/assoc-const.rs
+++ /dev/null
@@ -1,22 +0,0 @@
-//@ run-pass
-
-#![feature(supertrait_item_shadowing)]
-#![allow(dead_code)]
-
-trait A {
-    const CONST: i32;
-}
-impl<T> A for T {
-    const CONST: i32 = 1;
-}
-
-trait B: A {
-    const CONST: i32;
-}
-impl<T> B for T {
-    const CONST: i32 = 2;
-}
-
-fn main() {
-    assert_eq!(i32::CONST, 2)
-}
diff --git a/tests/ui/methods/supertrait-shadowing/common-ancestor-2.rs b/tests/ui/methods/supertrait-shadowing/common-ancestor-2.rs
deleted file mode 100644
index ce56c25df19ea..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/common-ancestor-2.rs
+++ /dev/null
@@ -1,33 +0,0 @@
-//@ run-pass
-
-#![feature(supertrait_item_shadowing)]
-#![warn(resolving_to_items_shadowing_supertrait_items)]
-#![warn(shadowing_supertrait_items)]
-#![allow(dead_code)]
-
-trait A {
-    fn hello(&self) -> &'static str {
-        "A"
-    }
-}
-impl<T> A for T {}
-
-trait B {
-    fn hello(&self) -> &'static str {
-        "B"
-    }
-}
-impl<T> B for T {}
-
-trait C: A + B {
-    fn hello(&self) -> &'static str {
-        //~^ WARN trait item `hello` from `C` shadows identically named item
-        "C"
-    }
-}
-impl<T> C for T {}
-
-fn main() {
-    assert_eq!(().hello(), "C");
-    //~^ WARN trait item `hello` from `C` shadows identically named item from supertrait
-}
diff --git a/tests/ui/methods/supertrait-shadowing/common-ancestor-3.rs b/tests/ui/methods/supertrait-shadowing/common-ancestor-3.rs
deleted file mode 100644
index b29f3c8d014ec..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/common-ancestor-3.rs
+++ /dev/null
@@ -1,43 +0,0 @@
-//@ run-pass
-
-#![feature(supertrait_item_shadowing)]
-#![warn(resolving_to_items_shadowing_supertrait_items)]
-#![warn(shadowing_supertrait_items)]
-#![allow(dead_code)]
-
-trait A {
-    fn hello(&self) -> &'static str {
-        "A"
-    }
-}
-impl<T> A for T {}
-
-trait B {
-    fn hello(&self) -> &'static str {
-        "B"
-    }
-}
-impl<T> B for T {}
-
-trait C: A + B {
-    fn hello(&self) -> &'static str {
-        //~^ WARN trait item `hello` from `C` shadows identically named item
-        "C"
-    }
-}
-impl<T> C for T {}
-
-// `D` extends `C` which extends `B` and `A`
-
-trait D: C {
-    fn hello(&self) -> &'static str {
-        //~^ WARN trait item `hello` from `D` shadows identically named item
-        "D"
-    }
-}
-impl<T> D for T {}
-
-fn main() {
-    assert_eq!(().hello(), "D");
-    //~^ WARN trait item `hello` from `D` shadows identically named item from supertrait
-}
diff --git a/tests/ui/methods/supertrait-shadowing/common-ancestor-3.stderr b/tests/ui/methods/supertrait-shadowing/common-ancestor-3.stderr
deleted file mode 100644
index 28fe7f72f94c3..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/common-ancestor-3.stderr
+++ /dev/null
@@ -1,68 +0,0 @@
-warning: trait item `hello` from `C` shadows identically named item from supertrait
-  --> $DIR/common-ancestor-3.rs:23:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: items from several supertraits are shadowed: `B` and `A`
-  --> $DIR/common-ancestor-3.rs:9:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-...
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: the lint level is defined here
-  --> $DIR/common-ancestor-3.rs:5:9
-   |
-LL | #![warn(shadowing_supertrait_items)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-warning: trait item `hello` from `D` shadows identically named item from supertrait
-  --> $DIR/common-ancestor-3.rs:33:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: items from several supertraits are shadowed: `C`, `B`, and `A`
-  --> $DIR/common-ancestor-3.rs:9:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-...
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-...
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-warning: trait item `hello` from `D` shadows identically named item from supertrait
-  --> $DIR/common-ancestor-3.rs:41:19
-   |
-LL |     assert_eq!(().hello(), "D");
-   |                   ^^^^^
-   |
-note: item from `D` shadows a supertrait item
-  --> $DIR/common-ancestor-3.rs:33:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: items from several supertraits are shadowed: `A`, `B`, and `C`
-  --> $DIR/common-ancestor-3.rs:9:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-...
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-...
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: the lint level is defined here
-  --> $DIR/common-ancestor-3.rs:4:9
-   |
-LL | #![warn(resolving_to_items_shadowing_supertrait_items)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-warning: 3 warnings emitted
-
diff --git a/tests/ui/methods/supertrait-shadowing/common-ancestor.rs b/tests/ui/methods/supertrait-shadowing/common-ancestor.rs
deleted file mode 100644
index b288d6e22b8c3..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/common-ancestor.rs
+++ /dev/null
@@ -1,26 +0,0 @@
-//@ run-pass
-
-#![feature(supertrait_item_shadowing)]
-#![warn(resolving_to_items_shadowing_supertrait_items)]
-#![warn(shadowing_supertrait_items)]
-#![allow(dead_code)]
-
-trait A {
-    fn hello(&self) -> &'static str {
-        "A"
-    }
-}
-impl<T> A for T {}
-
-trait B: A {
-    fn hello(&self) -> &'static str {
-        //~^ WARN trait item `hello` from `B` shadows identically named item
-        "B"
-    }
-}
-impl<T> B for T {}
-
-fn main() {
-    assert_eq!(().hello(), "B");
-    //~^ WARN trait item `hello` from `B` shadows identically named item from supertrait
-}
diff --git a/tests/ui/methods/supertrait-shadowing/definition-site.rs b/tests/ui/methods/supertrait-shadowing/definition-site.rs
deleted file mode 100644
index 248df032736f6..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/definition-site.rs
+++ /dev/null
@@ -1,18 +0,0 @@
-#![feature(supertrait_item_shadowing)]
-#![deny(shadowing_supertrait_items)]
-
-trait SuperSuper {
-    fn method();
-}
-
-trait Super: SuperSuper {
-    fn method();
-    //~^ ERROR trait item `method` from `Super` shadows identically named item
-}
-
-trait Sub: Super {
-    fn method();
-    //~^ ERROR trait item `method` from `Sub` shadows identically named item
-}
-
-fn main() {}
diff --git a/tests/ui/methods/supertrait-shadowing/definition-site.stderr b/tests/ui/methods/supertrait-shadowing/definition-site.stderr
deleted file mode 100644
index 1e35a753a9ebc..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/definition-site.stderr
+++ /dev/null
@@ -1,34 +0,0 @@
-error: trait item `method` from `Super` shadows identically named item from supertrait
-  --> $DIR/definition-site.rs:9:5
-   |
-LL |     fn method();
-   |     ^^^^^^^^^^^^
-   |
-note: item from `SuperSuper` is shadowed by a subtrait item
-  --> $DIR/definition-site.rs:5:5
-   |
-LL |     fn method();
-   |     ^^^^^^^^^^^^
-note: the lint level is defined here
-  --> $DIR/definition-site.rs:2:9
-   |
-LL | #![deny(shadowing_supertrait_items)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: trait item `method` from `Sub` shadows identically named item from supertrait
-  --> $DIR/definition-site.rs:14:5
-   |
-LL |     fn method();
-   |     ^^^^^^^^^^^^
-   |
-note: items from several supertraits are shadowed: `Super` and `SuperSuper`
-  --> $DIR/definition-site.rs:5:5
-   |
-LL |     fn method();
-   |     ^^^^^^^^^^^^
-...
-LL |     fn method();
-   |     ^^^^^^^^^^^^
-
-error: aborting due to 2 previous errors
-
diff --git a/tests/ui/methods/supertrait-shadowing/no-common-ancestor-2.rs b/tests/ui/methods/supertrait-shadowing/no-common-ancestor-2.rs
deleted file mode 100644
index b49476c7a4f68..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/no-common-ancestor-2.rs
+++ /dev/null
@@ -1,37 +0,0 @@
-#![feature(supertrait_item_shadowing)]
-
-trait A {
-    fn hello(&self) -> &'static str {
-        "A"
-    }
-}
-impl<T> A for T {}
-
-trait B {
-    fn hello(&self) -> &'static str {
-        "B"
-    }
-}
-impl<T> B for T {}
-
-trait C: A + B {
-    fn hello(&self) -> &'static str {
-        "C"
-    }
-}
-impl<T> C for T {}
-
-// Since `D` is not a subtrait of `C`,
-// we have no obvious lower bound.
-
-trait D: B {
-    fn hello(&self) -> &'static str {
-        "D"
-    }
-}
-impl<T> D for T {}
-
-fn main() {
-    ().hello();
-    //~^ ERROR multiple applicable items in scope
-}
diff --git a/tests/ui/methods/supertrait-shadowing/no-common-ancestor-2.stderr b/tests/ui/methods/supertrait-shadowing/no-common-ancestor-2.stderr
deleted file mode 100644
index 745f61d00d660..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/no-common-ancestor-2.stderr
+++ /dev/null
@@ -1,50 +0,0 @@
-error[E0034]: multiple applicable items in scope
-  --> $DIR/no-common-ancestor-2.rs:35:8
-   |
-LL |     ().hello();
-   |        ^^^^^ multiple `hello` found
-   |
-note: candidate #1 is defined in an impl of the trait `A` for the type `T`
-  --> $DIR/no-common-ancestor-2.rs:4:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: candidate #2 is defined in an impl of the trait `B` for the type `T`
-  --> $DIR/no-common-ancestor-2.rs:11:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: candidate #3 is defined in an impl of the trait `C` for the type `T`
-  --> $DIR/no-common-ancestor-2.rs:18:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: candidate #4 is defined in an impl of the trait `D` for the type `T`
-  --> $DIR/no-common-ancestor-2.rs:28:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-help: disambiguate the method for candidate #1
-   |
-LL -     ().hello();
-LL +     A::hello(&());
-   |
-help: disambiguate the method for candidate #2
-   |
-LL -     ().hello();
-LL +     B::hello(&());
-   |
-help: disambiguate the method for candidate #3
-   |
-LL -     ().hello();
-LL +     C::hello(&());
-   |
-help: disambiguate the method for candidate #4
-   |
-LL -     ().hello();
-LL +     D::hello(&());
-   |
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0034`.
diff --git a/tests/ui/methods/supertrait-shadowing/no-common-ancestor.rs b/tests/ui/methods/supertrait-shadowing/no-common-ancestor.rs
deleted file mode 100644
index 03c822eb7375e..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/no-common-ancestor.rs
+++ /dev/null
@@ -1,20 +0,0 @@
-#![feature(supertrait_item_shadowing)]
-
-trait A {
-    fn hello(&self) -> &'static str {
-        "A"
-    }
-}
-impl<T> A for T {}
-
-trait B {
-    fn hello(&self) -> &'static str {
-        "B"
-    }
-}
-impl<T> B for T {}
-
-fn main() {
-    ().hello();
-    //~^ ERROR multiple applicable items in scope
-}
diff --git a/tests/ui/methods/supertrait-shadowing/no-common-ancestor.stderr b/tests/ui/methods/supertrait-shadowing/no-common-ancestor.stderr
deleted file mode 100644
index 29cf7ff1dbb11..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/no-common-ancestor.stderr
+++ /dev/null
@@ -1,30 +0,0 @@
-error[E0034]: multiple applicable items in scope
-  --> $DIR/no-common-ancestor.rs:18:8
-   |
-LL |     ().hello();
-   |        ^^^^^ multiple `hello` found
-   |
-note: candidate #1 is defined in an impl of the trait `A` for the type `T`
-  --> $DIR/no-common-ancestor.rs:4:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: candidate #2 is defined in an impl of the trait `B` for the type `T`
-  --> $DIR/no-common-ancestor.rs:11:5
-   |
-LL |     fn hello(&self) -> &'static str {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-help: disambiguate the method for candidate #1
-   |
-LL -     ().hello();
-LL +     A::hello(&());
-   |
-help: disambiguate the method for candidate #2
-   |
-LL -     ().hello();
-LL +     B::hello(&());
-   |
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0034`.
diff --git a/tests/ui/methods/supertrait-shadowing/out-of-scope.rs b/tests/ui/methods/supertrait-shadowing/out-of-scope.rs
deleted file mode 100644
index 4112634399b78..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/out-of-scope.rs
+++ /dev/null
@@ -1,23 +0,0 @@
-//@ run-pass
-
-#![allow(dead_code)]
-
-mod out_of_scope {
-    pub trait Subtrait: super::Supertrait {
-        fn hello(&self) -> &'static str {
-            "subtrait"
-        }
-    }
-    impl<T> Subtrait for T {}
-}
-
-trait Supertrait {
-    fn hello(&self) -> &'static str {
-        "supertrait"
-    }
-}
-impl<T> Supertrait for T {}
-
-fn main() {
-    assert_eq!(().hello(), "supertrait");
-}
diff --git a/tests/ui/methods/supertrait-shadowing/type-dependent.rs b/tests/ui/methods/supertrait-shadowing/type-dependent.rs
deleted file mode 100644
index 4a5af1d598812..0000000000000
--- a/tests/ui/methods/supertrait-shadowing/type-dependent.rs
+++ /dev/null
@@ -1,28 +0,0 @@
-//@ run-pass
-
-// Makes sure we can shadow with type-dependent method syntax.
-
-#![feature(supertrait_item_shadowing)]
-#![allow(dead_code)]
-
-trait A {
-    fn hello() -> &'static str {
-        "A"
-    }
-}
-impl<T> A for T {}
-
-trait B: A {
-    fn hello() -> &'static str {
-        "B"
-    }
-}
-impl<T> B for T {}
-
-fn foo<T>() -> &'static str {
-    T::hello()
-}
-
-fn main() {
-    assert_eq!(foo::<()>(), "B");
-}
diff --git a/tests/ui/supertrait-shadowing/assoc-const.rs b/tests/ui/supertrait-shadowing/assoc-const.rs
new file mode 100644
index 0000000000000..be0d990284b0c
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/assoc-const.rs
@@ -0,0 +1,31 @@
+//@ run-pass
+
+#![feature(supertrait_item_shadowing)]
+#![feature(min_generic_const_args)]
+#![allow(dead_code)]
+
+trait A {
+    const CONST: i32;
+}
+impl<T> A for T {
+    const CONST: i32 = 1;
+}
+
+trait B: A {
+    type const CONST: i32;
+}
+impl<T> B for T {
+    type const CONST: i32 = 2;
+}
+
+trait C: B {}
+impl<T> C for T {}
+
+fn main() {
+    assert_eq!(i32::CONST, 2);
+    generic::<u32>();
+}
+
+fn generic<T: C<CONST = 2>>() {
+    assert_eq!(T::CONST, 2);
+}
diff --git a/tests/ui/supertrait-shadowing/assoc-type-fail.rs b/tests/ui/supertrait-shadowing/assoc-type-fail.rs
new file mode 100644
index 0000000000000..5df4edb7e96e2
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/assoc-type-fail.rs
@@ -0,0 +1,47 @@
+#![feature(supertrait_item_shadowing)]
+#![allow(dead_code)]
+
+use std::mem::size_of;
+
+trait A {
+    type Assoc;
+}
+impl<X> A for X {
+    type Assoc = i8;
+}
+
+trait B: A {
+    type Assoc;
+}
+impl<X> B for X {
+    type Assoc = i16;
+}
+
+trait C: B {}
+impl<X> C for X {}
+
+fn main() {
+    b_unbound::<u32>();
+    c_unbound::<u32>();
+
+    b_assoc_is_a::<u32>();
+    //~^ ERROR type mismatch resolving `<u32 as B>::Assoc == i8`
+    c_assoc_is_a::<u32>();
+    //~^ ERROR type mismatch resolving `<u32 as B>::Assoc == i8`
+}
+
+fn b_unbound<U: B>() {
+    let _ = size_of::<U::Assoc>();
+}
+
+fn c_unbound<U: C>() {
+    let _ = size_of::<U::Assoc>();
+}
+
+fn b_assoc_is_a<U: B<Assoc = i8>>() {
+    let _ = size_of::<U::Assoc>();
+}
+
+fn c_assoc_is_a<U: C<Assoc = i8>>() {
+    let _ = size_of::<U::Assoc>();
+}
diff --git a/tests/ui/supertrait-shadowing/assoc-type-fail.stderr b/tests/ui/supertrait-shadowing/assoc-type-fail.stderr
new file mode 100644
index 0000000000000..36a9bd082aaf6
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/assoc-type-fail.stderr
@@ -0,0 +1,37 @@
+error[E0271]: type mismatch resolving `<u32 as B>::Assoc == i8`
+  --> $DIR/assoc-type-fail.rs:27:20
+   |
+LL |     b_assoc_is_a::<u32>();
+   |                    ^^^ type mismatch resolving `<u32 as B>::Assoc == i8`
+   |
+note: expected this to be `i8`
+  --> $DIR/assoc-type-fail.rs:17:18
+   |
+LL |     type Assoc = i16;
+   |                  ^^^
+note: required by a bound in `b_assoc_is_a`
+  --> $DIR/assoc-type-fail.rs:41:22
+   |
+LL | fn b_assoc_is_a<U: B<Assoc = i8>>() {
+   |                      ^^^^^^^^^^ required by this bound in `b_assoc_is_a`
+
+error[E0271]: type mismatch resolving `<u32 as B>::Assoc == i8`
+  --> $DIR/assoc-type-fail.rs:29:20
+   |
+LL |     c_assoc_is_a::<u32>();
+   |                    ^^^ type mismatch resolving `<u32 as B>::Assoc == i8`
+   |
+note: expected this to be `i8`
+  --> $DIR/assoc-type-fail.rs:17:18
+   |
+LL |     type Assoc = i16;
+   |                  ^^^
+note: required by a bound in `c_assoc_is_a`
+  --> $DIR/assoc-type-fail.rs:45:22
+   |
+LL | fn c_assoc_is_a<U: C<Assoc = i8>>() {
+   |                      ^^^^^^^^^^ required by this bound in `c_assoc_is_a`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0271`.
diff --git a/tests/ui/supertrait-shadowing/assoc-type-predicates.rs b/tests/ui/supertrait-shadowing/assoc-type-predicates.rs
new file mode 100644
index 0000000000000..55d2b84a50f9a
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/assoc-type-predicates.rs
@@ -0,0 +1,45 @@
+//@ normalize-stderr: "assoc_type_predicates\[[^\]]+\]" -> "assoc_type_predicates[HASH]"
+
+#![feature(rustc_attrs)]
+#![feature(supertrait_item_shadowing)]
+#![allow(dead_code)]
+
+trait A {
+    type Assoc;
+}
+impl<T> A for T {
+    type Assoc = i8;
+}
+
+trait B: A {
+    type Assoc;
+}
+impl<T> B for T {
+    type Assoc = i16;
+}
+
+trait C: B {}
+impl<T> C for T {}
+
+#[rustc_dump_predicates]
+fn a_bound<T: A<Assoc = i8>>() {}
+//~^ ERROR rustc_dump_predicates
+//~| NOTE TraitPredicate(<T as std::marker::Sized>
+//~| NOTE TraitPredicate(<T as A>
+//~| NOTE A::Assoc
+
+#[rustc_dump_predicates]
+fn b_bound<T: B<Assoc = i16>>() {}
+//~^ ERROR rustc_dump_predicates
+//~| NOTE TraitPredicate(<T as std::marker::Sized>
+//~| NOTE TraitPredicate(<T as B>
+//~| NOTE B::Assoc
+
+#[rustc_dump_predicates]
+fn c_bound<T: C<Assoc = i16>>() {}
+//~^ ERROR rustc_dump_predicates
+//~| NOTE TraitPredicate(<T as std::marker::Sized>
+//~| NOTE TraitPredicate(<T as C>
+//~| NOTE B::Assoc
+
+fn main() {}
diff --git a/tests/ui/supertrait-shadowing/assoc-type-predicates.stderr b/tests/ui/supertrait-shadowing/assoc-type-predicates.stderr
new file mode 100644
index 0000000000000..be765e737a6e1
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/assoc-type-predicates.stderr
@@ -0,0 +1,32 @@
+error: rustc_dump_predicates
+  --> $DIR/assoc-type-predicates.rs:25:1
+   |
+LL | fn a_bound<T: A<Assoc = i8>>() {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: Binder { value: TraitPredicate(<T as std::marker::Sized>, polarity:Positive), bound_vars: [] }
+   = note: Binder { value: TraitPredicate(<T as A>, polarity:Positive), bound_vars: [] }
+   = note: Binder { value: ProjectionPredicate(Alias { kind: ProjectionTy { def_id: DefId(0:4 ~ assoc_type_predicates[HASH]::A::Assoc) }, args: [T/#0], .. }, Term::Ty(i8)), bound_vars: [] }
+
+error: rustc_dump_predicates
+  --> $DIR/assoc-type-predicates.rs:32:1
+   |
+LL | fn b_bound<T: B<Assoc = i16>>() {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: Binder { value: TraitPredicate(<T as std::marker::Sized>, polarity:Positive), bound_vars: [] }
+   = note: Binder { value: TraitPredicate(<T as B>, polarity:Positive), bound_vars: [] }
+   = note: Binder { value: ProjectionPredicate(Alias { kind: ProjectionTy { def_id: DefId(0:9 ~ assoc_type_predicates[HASH]::B::Assoc) }, args: [T/#0], .. }, Term::Ty(i16)), bound_vars: [] }
+
+error: rustc_dump_predicates
+  --> $DIR/assoc-type-predicates.rs:39:1
+   |
+LL | fn c_bound<T: C<Assoc = i16>>() {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: Binder { value: TraitPredicate(<T as std::marker::Sized>, polarity:Positive), bound_vars: [] }
+   = note: Binder { value: TraitPredicate(<T as C>, polarity:Positive), bound_vars: [] }
+   = note: Binder { value: ProjectionPredicate(Alias { kind: ProjectionTy { def_id: DefId(0:9 ~ assoc_type_predicates[HASH]::B::Assoc) }, args: [T/#0], .. }, Term::Ty(i16)), bound_vars: [] }
+
+error: aborting due to 3 previous errors
+
diff --git a/tests/ui/supertrait-shadowing/assoc-type.rs b/tests/ui/supertrait-shadowing/assoc-type.rs
new file mode 100644
index 0000000000000..9e9799397c571
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/assoc-type.rs
@@ -0,0 +1,53 @@
+//@ run-pass
+//@ check-run-results
+
+#![feature(supertrait_item_shadowing)]
+#![allow(dead_code)]
+
+use std::mem::size_of;
+
+trait A {
+    type Assoc;
+}
+impl<T> A for T {
+    type Assoc = i8;
+}
+
+trait B: A {
+    type Assoc;
+}
+impl<T> B for T {
+    type Assoc = i16;
+}
+
+trait C: B {}
+impl<T> C for T {}
+
+fn main() {
+    generic::<u32>();
+    generic2::<u32>();
+    generic3::<u32>();
+    generic4::<u32>();
+    generic5::<u32>();
+}
+
+fn generic<T: B>() {
+    assert_eq!(size_of::<T::Assoc>(), 2);
+}
+
+fn generic2<T: A<Assoc = i8>>() {
+    assert_eq!(size_of::<T::Assoc>(), 1);
+}
+
+fn generic3<T: B<Assoc = i16>>() {
+    assert_eq!(size_of::<T::Assoc>(), 2);
+}
+
+fn generic4<T: C<Assoc = i16>>() {
+    assert_eq!(size_of::<T::Assoc>(), 2);
+}
+
+fn generic5<T: B>() {
+    assert_eq!(size_of::<<T as A>::Assoc>(), 1);
+    assert_eq!(size_of::<<T as B>::Assoc>(), 2);
+}
diff --git a/tests/ui/methods/supertrait-shadowing/auxiliary/shadowed_stability.rs b/tests/ui/supertrait-shadowing/auxiliary/shadowed_stability.rs
similarity index 100%
rename from tests/ui/methods/supertrait-shadowing/auxiliary/shadowed_stability.rs
rename to tests/ui/supertrait-shadowing/auxiliary/shadowed_stability.rs
diff --git a/tests/ui/supertrait-shadowing/common-ancestor-2.rs b/tests/ui/supertrait-shadowing/common-ancestor-2.rs
new file mode 100644
index 0000000000000..908c5d2bf2199
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/common-ancestor-2.rs
@@ -0,0 +1,59 @@
+//@ run-pass
+
+#![feature(supertrait_item_shadowing)]
+#![feature(min_generic_const_args)]
+#![warn(resolving_to_items_shadowing_supertrait_items)]
+#![warn(shadowing_supertrait_items)]
+#![allow(dead_code)]
+
+use std::mem::size_of;
+
+trait A {
+    fn hello(&self) -> &'static str {
+        "A"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> A for T {
+    type Assoc = i8;
+    const CONST: i32 = 1;
+}
+
+trait B {
+    fn hello(&self) -> &'static str {
+        "B"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> B for T {
+    type Assoc = i16;
+    const CONST: i32 = 2;
+}
+
+trait C: A + B {
+    fn hello(&self) -> &'static str {
+        //~^ WARN trait item `hello` from `C` shadows identically named item
+        "C"
+    }
+    type Assoc;
+    //~^ WARN trait item `Assoc` from `C` shadows identically named item
+    type const CONST: i32;
+    //~^ WARN trait item `CONST` from `C` shadows identically named item
+}
+impl<T> C for T {
+    type Assoc = i32;
+    type const CONST: i32 = 3;
+}
+
+fn main() {
+    assert_eq!(().hello(), "C");
+    //~^ WARN trait item `hello` from `C` shadows identically named item from supertrait
+    check::<()>();
+}
+
+fn check<T: C>() {
+    assert_eq!(size_of::<T::Assoc>(), 4);
+    assert_eq!(T::CONST, 3);
+}
diff --git a/tests/ui/methods/supertrait-shadowing/common-ancestor-2.stderr b/tests/ui/supertrait-shadowing/common-ancestor-2.stderr
similarity index 55%
rename from tests/ui/methods/supertrait-shadowing/common-ancestor-2.stderr
rename to tests/ui/supertrait-shadowing/common-ancestor-2.stderr
index b0f61b46b6911..646726b835041 100644
--- a/tests/ui/methods/supertrait-shadowing/common-ancestor-2.stderr
+++ b/tests/ui/supertrait-shadowing/common-ancestor-2.stderr
@@ -1,11 +1,11 @@
 warning: trait item `hello` from `C` shadows identically named item from supertrait
-  --> $DIR/common-ancestor-2.rs:23:5
+  --> $DIR/common-ancestor-2.rs:36:5
    |
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: items from several supertraits are shadowed: `B` and `A`
-  --> $DIR/common-ancestor-2.rs:9:5
+  --> $DIR/common-ancestor-2.rs:12:5
    |
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -13,24 +13,54 @@ LL |     fn hello(&self) -> &'static str {
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: the lint level is defined here
-  --> $DIR/common-ancestor-2.rs:5:9
+  --> $DIR/common-ancestor-2.rs:6:9
    |
 LL | #![warn(shadowing_supertrait_items)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+warning: trait item `Assoc` from `C` shadows identically named item from supertrait
+  --> $DIR/common-ancestor-2.rs:40:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `B` and `A`
+  --> $DIR/common-ancestor-2.rs:15:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+...
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+
+warning: trait item `CONST` from `C` shadows identically named item from supertrait
+  --> $DIR/common-ancestor-2.rs:42:5
+   |
+LL |     type const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `B` and `A`
+  --> $DIR/common-ancestor-2.rs:16:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+...
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+
 warning: trait item `hello` from `C` shadows identically named item from supertrait
-  --> $DIR/common-ancestor-2.rs:31:19
+  --> $DIR/common-ancestor-2.rs:51:19
    |
 LL |     assert_eq!(().hello(), "C");
    |                   ^^^^^
    |
 note: item from `C` shadows a supertrait item
-  --> $DIR/common-ancestor-2.rs:23:5
+  --> $DIR/common-ancestor-2.rs:36:5
    |
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: items from several supertraits are shadowed: `A` and `B`
-  --> $DIR/common-ancestor-2.rs:9:5
+  --> $DIR/common-ancestor-2.rs:12:5
    |
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -38,10 +68,10 @@ LL |     fn hello(&self) -> &'static str {
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: the lint level is defined here
-  --> $DIR/common-ancestor-2.rs:4:9
+  --> $DIR/common-ancestor-2.rs:5:9
    |
 LL | #![warn(resolving_to_items_shadowing_supertrait_items)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-warning: 2 warnings emitted
+warning: 4 warnings emitted
 
diff --git a/tests/ui/supertrait-shadowing/common-ancestor-3.rs b/tests/ui/supertrait-shadowing/common-ancestor-3.rs
new file mode 100644
index 0000000000000..ade23ca88aec2
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/common-ancestor-3.rs
@@ -0,0 +1,76 @@
+//@ run-pass
+
+#![feature(supertrait_item_shadowing)]
+#![feature(min_generic_const_args)]
+#![warn(resolving_to_items_shadowing_supertrait_items)]
+#![warn(shadowing_supertrait_items)]
+#![allow(dead_code)]
+
+use std::mem::size_of;
+
+trait A {
+    fn hello(&self) -> &'static str {
+        "A"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> A for T {
+    type Assoc = i8;
+    const CONST: i32 = 1;
+}
+
+trait B {
+    fn hello(&self) -> &'static str {
+        "B"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> B for T {
+    type Assoc = i16;
+    const CONST: i32 = 2;
+}
+
+trait C: A + B {
+    fn hello(&self) -> &'static str {
+        //~^ WARN trait item `hello` from `C` shadows identically named item
+        "C"
+    }
+    type Assoc;
+    //~^ WARN trait item `Assoc` from `C` shadows identically named item
+    type const CONST: i32;
+    //~^ WARN trait item `CONST` from `C` shadows identically named item
+}
+impl<T> C for T {
+    type Assoc = i32;
+    type const CONST: i32 = 3;
+}
+
+// `D` extends `C` which extends `B` and `A`
+
+trait D: C {
+    fn hello(&self) -> &'static str {
+        //~^ WARN trait item `hello` from `D` shadows identically named item
+        "D"
+    }
+    type Assoc;
+    //~^ WARN trait item `Assoc` from `D` shadows identically named item
+    type const CONST: i32;
+    //~^ WARN trait item `CONST` from `D` shadows identically named item
+}
+impl<T> D for T {
+    type Assoc = i64;
+    type const CONST: i32 = 4;
+}
+
+fn main() {
+    assert_eq!(().hello(), "D");
+    //~^ WARN trait item `hello` from `D` shadows identically named item from supertrait
+    check::<()>();
+}
+
+fn check<T: D>() {
+    assert_eq!(size_of::<T::Assoc>(), 8);
+    assert_eq!(T::CONST, 4);
+}
diff --git a/tests/ui/supertrait-shadowing/common-ancestor-3.stderr b/tests/ui/supertrait-shadowing/common-ancestor-3.stderr
new file mode 100644
index 0000000000000..62132832da4ba
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/common-ancestor-3.stderr
@@ -0,0 +1,134 @@
+warning: trait item `hello` from `C` shadows identically named item from supertrait
+  --> $DIR/common-ancestor-3.rs:36:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `B` and `A`
+  --> $DIR/common-ancestor-3.rs:12:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: the lint level is defined here
+  --> $DIR/common-ancestor-3.rs:6:9
+   |
+LL | #![warn(shadowing_supertrait_items)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: trait item `Assoc` from `C` shadows identically named item from supertrait
+  --> $DIR/common-ancestor-3.rs:40:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `B` and `A`
+  --> $DIR/common-ancestor-3.rs:15:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+...
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+
+warning: trait item `CONST` from `C` shadows identically named item from supertrait
+  --> $DIR/common-ancestor-3.rs:42:5
+   |
+LL |     type const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `B` and `A`
+  --> $DIR/common-ancestor-3.rs:16:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+...
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+
+warning: trait item `hello` from `D` shadows identically named item from supertrait
+  --> $DIR/common-ancestor-3.rs:53:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `C`, `B`, and `A`
+  --> $DIR/common-ancestor-3.rs:12:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: trait item `Assoc` from `D` shadows identically named item from supertrait
+  --> $DIR/common-ancestor-3.rs:57:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `C`, `B`, and `A`
+  --> $DIR/common-ancestor-3.rs:15:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+...
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+...
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+
+warning: trait item `CONST` from `D` shadows identically named item from supertrait
+  --> $DIR/common-ancestor-3.rs:59:5
+   |
+LL |     type const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `C`, `B`, and `A`
+  --> $DIR/common-ancestor-3.rs:16:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+...
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+...
+LL |     type const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+warning: trait item `hello` from `D` shadows identically named item from supertrait
+  --> $DIR/common-ancestor-3.rs:68:19
+   |
+LL |     assert_eq!(().hello(), "D");
+   |                   ^^^^^
+   |
+note: item from `D` shadows a supertrait item
+  --> $DIR/common-ancestor-3.rs:53:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: items from several supertraits are shadowed: `A`, `B`, and `C`
+  --> $DIR/common-ancestor-3.rs:12:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: the lint level is defined here
+  --> $DIR/common-ancestor-3.rs:5:9
+   |
+LL | #![warn(resolving_to_items_shadowing_supertrait_items)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: 7 warnings emitted
+
diff --git a/tests/ui/supertrait-shadowing/common-ancestor.rs b/tests/ui/supertrait-shadowing/common-ancestor.rs
new file mode 100644
index 0000000000000..903f85957870b
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/common-ancestor.rs
@@ -0,0 +1,47 @@
+//@ run-pass
+
+#![feature(supertrait_item_shadowing)]
+#![feature(min_generic_const_args)]
+#![warn(resolving_to_items_shadowing_supertrait_items)]
+#![warn(shadowing_supertrait_items)]
+#![allow(dead_code)]
+
+use std::mem::size_of;
+
+trait A {
+    fn hello(&self) -> &'static str {
+        "A"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> A for T {
+    type Assoc = i8;
+    const CONST: i32 = 1;
+}
+
+trait B: A {
+    fn hello(&self) -> &'static str {
+        //~^ WARN trait item `hello` from `B` shadows identically named item
+        "B"
+    }
+    type Assoc;
+    //~^ WARN trait item `Assoc` from `B` shadows identically named item
+    type const CONST: i32;
+    //~^ WARN trait item `CONST` from `B` shadows identically named item
+}
+impl<T> B for T {
+    type Assoc = i16;
+    type const CONST: i32 = 2;
+}
+
+fn main() {
+    assert_eq!(().hello(), "B");
+    //~^ WARN trait item `hello` from `B` shadows identically named item from supertrait
+    check::<()>();
+}
+
+fn check<T: B>() {
+    assert_eq!(size_of::<T::Assoc>(), 2);
+    assert_eq!(T::CONST, 2);
+}
diff --git a/tests/ui/methods/supertrait-shadowing/common-ancestor.stderr b/tests/ui/supertrait-shadowing/common-ancestor.stderr
similarity index 56%
rename from tests/ui/methods/supertrait-shadowing/common-ancestor.stderr
rename to tests/ui/supertrait-shadowing/common-ancestor.stderr
index 9afedeab5e2c2..9b13537cf800c 100644
--- a/tests/ui/methods/supertrait-shadowing/common-ancestor.stderr
+++ b/tests/ui/supertrait-shadowing/common-ancestor.stderr
@@ -1,41 +1,65 @@
 warning: trait item `hello` from `B` shadows identically named item from supertrait
-  --> $DIR/common-ancestor.rs:16:5
+  --> $DIR/common-ancestor.rs:24:5
    |
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: item from `A` is shadowed by a subtrait item
-  --> $DIR/common-ancestor.rs:9:5
+  --> $DIR/common-ancestor.rs:12:5
    |
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: the lint level is defined here
-  --> $DIR/common-ancestor.rs:5:9
+  --> $DIR/common-ancestor.rs:6:9
    |
 LL | #![warn(shadowing_supertrait_items)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+warning: trait item `Assoc` from `B` shadows identically named item from supertrait
+  --> $DIR/common-ancestor.rs:28:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+   |
+note: item from `A` is shadowed by a subtrait item
+  --> $DIR/common-ancestor.rs:15:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+
+warning: trait item `CONST` from `B` shadows identically named item from supertrait
+  --> $DIR/common-ancestor.rs:30:5
+   |
+LL |     type const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+note: item from `A` is shadowed by a subtrait item
+  --> $DIR/common-ancestor.rs:16:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+
 warning: trait item `hello` from `B` shadows identically named item from supertrait
-  --> $DIR/common-ancestor.rs:24:19
+  --> $DIR/common-ancestor.rs:39:19
    |
 LL |     assert_eq!(().hello(), "B");
    |                   ^^^^^
    |
 note: item from `B` shadows a supertrait item
-  --> $DIR/common-ancestor.rs:16:5
+  --> $DIR/common-ancestor.rs:24:5
    |
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: item from `A` is shadowed by a subtrait item
-  --> $DIR/common-ancestor.rs:9:5
+  --> $DIR/common-ancestor.rs:12:5
    |
 LL |     fn hello(&self) -> &'static str {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: the lint level is defined here
-  --> $DIR/common-ancestor.rs:4:9
+  --> $DIR/common-ancestor.rs:5:9
    |
 LL | #![warn(resolving_to_items_shadowing_supertrait_items)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-warning: 2 warnings emitted
+warning: 4 warnings emitted
 
diff --git a/tests/ui/supertrait-shadowing/definition-site.rs b/tests/ui/supertrait-shadowing/definition-site.rs
new file mode 100644
index 0000000000000..3309ee97e9f00
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/definition-site.rs
@@ -0,0 +1,28 @@
+#![feature(supertrait_item_shadowing)]
+#![deny(shadowing_supertrait_items)]
+
+trait SuperSuper {
+    fn method();
+    const CONST: i32;
+    type Assoc;
+}
+
+trait Super: SuperSuper {
+    fn method();
+    //~^ ERROR trait item `method` from `Super` shadows identically named item
+    const CONST: i32;
+    //~^ ERROR trait item `CONST` from `Super` shadows identically named item
+    type Assoc;
+    //~^ ERROR trait item `Assoc` from `Super` shadows identically named item
+}
+
+trait Sub: Super {
+    fn method();
+    //~^ ERROR trait item `method` from `Sub` shadows identically named item
+    const CONST: i32;
+    //~^ ERROR trait item `CONST` from `Sub` shadows identically named item
+    type Assoc;
+    //~^ ERROR trait item `Assoc` from `Sub` shadows identically named item
+}
+
+fn main() {}
diff --git a/tests/ui/supertrait-shadowing/definition-site.stderr b/tests/ui/supertrait-shadowing/definition-site.stderr
new file mode 100644
index 0000000000000..faf01cc711c6a
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/definition-site.stderr
@@ -0,0 +1,88 @@
+error: trait item `method` from `Super` shadows identically named item from supertrait
+  --> $DIR/definition-site.rs:11:5
+   |
+LL |     fn method();
+   |     ^^^^^^^^^^^^
+   |
+note: item from `SuperSuper` is shadowed by a subtrait item
+  --> $DIR/definition-site.rs:5:5
+   |
+LL |     fn method();
+   |     ^^^^^^^^^^^^
+note: the lint level is defined here
+  --> $DIR/definition-site.rs:2:9
+   |
+LL | #![deny(shadowing_supertrait_items)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: trait item `CONST` from `Super` shadows identically named item from supertrait
+  --> $DIR/definition-site.rs:13:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+   |
+note: item from `SuperSuper` is shadowed by a subtrait item
+  --> $DIR/definition-site.rs:6:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+
+error: trait item `Assoc` from `Super` shadows identically named item from supertrait
+  --> $DIR/definition-site.rs:15:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+   |
+note: item from `SuperSuper` is shadowed by a subtrait item
+  --> $DIR/definition-site.rs:7:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+
+error: trait item `method` from `Sub` shadows identically named item from supertrait
+  --> $DIR/definition-site.rs:20:5
+   |
+LL |     fn method();
+   |     ^^^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `Super` and `SuperSuper`
+  --> $DIR/definition-site.rs:5:5
+   |
+LL |     fn method();
+   |     ^^^^^^^^^^^^
+...
+LL |     fn method();
+   |     ^^^^^^^^^^^^
+
+error: trait item `CONST` from `Sub` shadows identically named item from supertrait
+  --> $DIR/definition-site.rs:22:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `Super` and `SuperSuper`
+  --> $DIR/definition-site.rs:6:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+...
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+
+error: trait item `Assoc` from `Sub` shadows identically named item from supertrait
+  --> $DIR/definition-site.rs:24:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+   |
+note: items from several supertraits are shadowed: `Super` and `SuperSuper`
+  --> $DIR/definition-site.rs:7:5
+   |
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+...
+LL |     type Assoc;
+   |     ^^^^^^^^^^
+
+error: aborting due to 6 previous errors
+
diff --git a/tests/ui/methods/supertrait-shadowing/false-subtrait-after-inference.rs b/tests/ui/supertrait-shadowing/false-subtrait-after-inference.rs
similarity index 100%
rename from tests/ui/methods/supertrait-shadowing/false-subtrait-after-inference.rs
rename to tests/ui/supertrait-shadowing/false-subtrait-after-inference.rs
diff --git a/tests/ui/methods/supertrait-shadowing/false-subtrait-after-inference.stderr b/tests/ui/supertrait-shadowing/false-subtrait-after-inference.stderr
similarity index 100%
rename from tests/ui/methods/supertrait-shadowing/false-subtrait-after-inference.stderr
rename to tests/ui/supertrait-shadowing/false-subtrait-after-inference.stderr
diff --git a/tests/ui/supertrait-shadowing/no-common-ancestor-2.rs b/tests/ui/supertrait-shadowing/no-common-ancestor-2.rs
new file mode 100644
index 0000000000000..957aabf5a51f8
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/no-common-ancestor-2.rs
@@ -0,0 +1,68 @@
+#![feature(supertrait_item_shadowing)]
+#![feature(min_generic_const_args)]
+
+use std::mem::size_of;
+
+trait A {
+    fn hello(&self) -> &'static str {
+        "A"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> A for T {
+    type Assoc = i8;
+    const CONST: i32 = 1;
+}
+
+trait B {
+    fn hello(&self) -> &'static str {
+        "B"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> B for T {
+    type Assoc = i16;
+    const CONST: i32 = 2;
+}
+
+trait C: A + B {
+    fn hello(&self) -> &'static str {
+        "C"
+    }
+    type Assoc;
+    type const CONST: i32;
+}
+impl<T> C for T {
+    type Assoc = i32;
+    type const CONST: i32 = 3;
+}
+
+// Since `D` is not a subtrait of `C`,
+// we have no obvious lower bound.
+
+trait D: B {
+    fn hello(&self) -> &'static str {
+        "D"
+    }
+    type Assoc;
+    type const CONST: i32;
+}
+impl<T> D for T {
+    type Assoc = i64;
+    type const CONST: i32 = 4;
+}
+
+fn main() {
+    ().hello();
+    //~^ ERROR multiple applicable items in scope
+    check::<()>();
+}
+
+fn check<T: C + D>() {
+    let _ = size_of::<T::Assoc>();
+    //~^ ERROR ambiguous associated type `Assoc` in bounds of `T`
+    let _ = T::CONST;
+    //~^ ERROR multiple applicable items in scope
+}
diff --git a/tests/ui/supertrait-shadowing/no-common-ancestor-2.stderr b/tests/ui/supertrait-shadowing/no-common-ancestor-2.stderr
new file mode 100644
index 0000000000000..987adcfbbe959
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/no-common-ancestor-2.stderr
@@ -0,0 +1,131 @@
+error[E0034]: multiple applicable items in scope
+  --> $DIR/no-common-ancestor-2.rs:58:8
+   |
+LL |     ().hello();
+   |        ^^^^^ multiple `hello` found
+   |
+note: candidate #1 is defined in an impl of the trait `A` for the type `T`
+  --> $DIR/no-common-ancestor-2.rs:7:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: candidate #2 is defined in an impl of the trait `B` for the type `T`
+  --> $DIR/no-common-ancestor-2.rs:19:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: candidate #3 is defined in an impl of the trait `C` for the type `T`
+  --> $DIR/no-common-ancestor-2.rs:31:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: candidate #4 is defined in an impl of the trait `D` for the type `T`
+  --> $DIR/no-common-ancestor-2.rs:46:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: disambiguate the method for candidate #1
+   |
+LL -     ().hello();
+LL +     A::hello(&());
+   |
+help: disambiguate the method for candidate #2
+   |
+LL -     ().hello();
+LL +     B::hello(&());
+   |
+help: disambiguate the method for candidate #3
+   |
+LL -     ().hello();
+LL +     C::hello(&());
+   |
+help: disambiguate the method for candidate #4
+   |
+LL -     ().hello();
+LL +     D::hello(&());
+   |
+
+error[E0221]: ambiguous associated type `Assoc` in bounds of `T`
+  --> $DIR/no-common-ancestor-2.rs:64:23
+   |
+LL |     type Assoc;
+   |     ---------- ambiguous `Assoc` from `A`
+...
+LL |     type Assoc;
+   |     ---------- ambiguous `Assoc` from `B`
+...
+LL |     type Assoc;
+   |     ---------- ambiguous `Assoc` from `C`
+...
+LL |     type Assoc;
+   |     ---------- ambiguous `Assoc` from `D`
+...
+LL |     let _ = size_of::<T::Assoc>();
+   |                       ^^^^^^^^ ambiguous associated type `Assoc`
+   |
+help: use fully-qualified syntax to disambiguate
+   |
+LL -     let _ = size_of::<T::Assoc>();
+LL +     let _ = size_of::<<T as A>::Assoc>();
+   |
+help: use fully-qualified syntax to disambiguate
+   |
+LL -     let _ = size_of::<T::Assoc>();
+LL +     let _ = size_of::<<T as C>::Assoc>();
+   |
+help: use fully-qualified syntax to disambiguate
+   |
+LL -     let _ = size_of::<T::Assoc>();
+LL +     let _ = size_of::<<T as B>::Assoc>();
+   |
+help: use fully-qualified syntax to disambiguate
+   |
+LL -     let _ = size_of::<T::Assoc>();
+LL +     let _ = size_of::<<T as D>::Assoc>();
+   |
+
+error[E0034]: multiple applicable items in scope
+  --> $DIR/no-common-ancestor-2.rs:66:16
+   |
+LL |     let _ = T::CONST;
+   |                ^^^^^ multiple `CONST` found
+   |
+note: candidate #1 is defined in the trait `A`
+  --> $DIR/no-common-ancestor-2.rs:11:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+note: candidate #2 is defined in the trait `B`
+  --> $DIR/no-common-ancestor-2.rs:23:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+note: candidate #3 is defined in the trait `C`
+  --> $DIR/no-common-ancestor-2.rs:35:5
+   |
+LL |     type const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^^^^^^
+note: candidate #4 is defined in the trait `D`
+  --> $DIR/no-common-ancestor-2.rs:50:5
+   |
+LL |     type const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^^^^^^
+help: use fully-qualified syntax to disambiguate
+   |
+LL -     let _ = T::CONST;
+LL +     let _ = <T as A>::CONST;
+   |
+LL -     let _ = T::CONST;
+LL +     let _ = <T as B>::CONST;
+   |
+LL -     let _ = T::CONST;
+LL +     let _ = <T as C>::CONST;
+   |
+LL -     let _ = T::CONST;
+LL +     let _ = <T as D>::CONST;
+   |
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0034, E0221.
+For more information about an error, try `rustc --explain E0034`.
diff --git a/tests/ui/supertrait-shadowing/no-common-ancestor.rs b/tests/ui/supertrait-shadowing/no-common-ancestor.rs
new file mode 100644
index 0000000000000..73209c015f8f5
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/no-common-ancestor.rs
@@ -0,0 +1,41 @@
+#![feature(supertrait_item_shadowing)]
+#![feature(min_generic_const_args)]
+
+use std::mem::size_of;
+
+trait A {
+    fn hello(&self) -> &'static str {
+        "A"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> A for T {
+    type Assoc = i8;
+    const CONST: i32 = 1;
+}
+
+trait B {
+    fn hello(&self) -> &'static str {
+        "B"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> B for T {
+    type Assoc = i16;
+    const CONST: i32 = 2;
+}
+
+fn main() {
+    ().hello();
+    //~^ ERROR multiple applicable items in scope
+    check::<()>();
+}
+
+fn check<T: A + B>() {
+    let _ = size_of::<T::Assoc>();
+    //~^ ERROR ambiguous associated type `Assoc` in bounds of `T`
+    let _ = T::CONST;
+    //~^ ERROR multiple applicable items in scope
+}
diff --git a/tests/ui/supertrait-shadowing/no-common-ancestor.stderr b/tests/ui/supertrait-shadowing/no-common-ancestor.stderr
new file mode 100644
index 0000000000000..78fd8f4670577
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/no-common-ancestor.stderr
@@ -0,0 +1,79 @@
+error[E0034]: multiple applicable items in scope
+  --> $DIR/no-common-ancestor.rs:31:8
+   |
+LL |     ().hello();
+   |        ^^^^^ multiple `hello` found
+   |
+note: candidate #1 is defined in an impl of the trait `A` for the type `T`
+  --> $DIR/no-common-ancestor.rs:7:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: candidate #2 is defined in an impl of the trait `B` for the type `T`
+  --> $DIR/no-common-ancestor.rs:19:5
+   |
+LL |     fn hello(&self) -> &'static str {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: disambiguate the method for candidate #1
+   |
+LL -     ().hello();
+LL +     A::hello(&());
+   |
+help: disambiguate the method for candidate #2
+   |
+LL -     ().hello();
+LL +     B::hello(&());
+   |
+
+error[E0221]: ambiguous associated type `Assoc` in bounds of `T`
+  --> $DIR/no-common-ancestor.rs:37:23
+   |
+LL |     type Assoc;
+   |     ---------- ambiguous `Assoc` from `A`
+...
+LL |     type Assoc;
+   |     ---------- ambiguous `Assoc` from `B`
+...
+LL |     let _ = size_of::<T::Assoc>();
+   |                       ^^^^^^^^ ambiguous associated type `Assoc`
+   |
+help: use fully-qualified syntax to disambiguate
+   |
+LL -     let _ = size_of::<T::Assoc>();
+LL +     let _ = size_of::<<T as A>::Assoc>();
+   |
+help: use fully-qualified syntax to disambiguate
+   |
+LL -     let _ = size_of::<T::Assoc>();
+LL +     let _ = size_of::<<T as B>::Assoc>();
+   |
+
+error[E0034]: multiple applicable items in scope
+  --> $DIR/no-common-ancestor.rs:39:16
+   |
+LL |     let _ = T::CONST;
+   |                ^^^^^ multiple `CONST` found
+   |
+note: candidate #1 is defined in the trait `A`
+  --> $DIR/no-common-ancestor.rs:11:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+note: candidate #2 is defined in the trait `B`
+  --> $DIR/no-common-ancestor.rs:23:5
+   |
+LL |     const CONST: i32;
+   |     ^^^^^^^^^^^^^^^^
+help: use fully-qualified syntax to disambiguate
+   |
+LL -     let _ = T::CONST;
+LL +     let _ = <T as A>::CONST;
+   |
+LL -     let _ = T::CONST;
+LL +     let _ = <T as B>::CONST;
+   |
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0034, E0221.
+For more information about an error, try `rustc --explain E0034`.
diff --git a/tests/ui/supertrait-shadowing/out-of-scope.rs b/tests/ui/supertrait-shadowing/out-of-scope.rs
new file mode 100644
index 0000000000000..7b2322843f1c3
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/out-of-scope.rs
@@ -0,0 +1,42 @@
+//@ run-pass
+
+#![feature(min_generic_const_args)]
+#![allow(dead_code)]
+
+use std::mem::size_of;
+
+mod out_of_scope {
+    pub trait Subtrait: super::Supertrait {
+        fn hello(&self) -> &'static str {
+            "subtrait"
+        }
+        type Assoc;
+        type const CONST: i32;
+    }
+    impl<T> Subtrait for T {
+        type Assoc = i16;
+        type const CONST: i32 = 2;
+    }
+}
+
+trait Supertrait {
+    fn hello(&self) -> &'static str {
+        "supertrait"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> Supertrait for T {
+    type Assoc = i8;
+    const CONST: i32 = 1;
+}
+
+fn main() {
+    assert_eq!(().hello(), "supertrait");
+    check::<()>();
+}
+
+fn check<T: Supertrait>() {
+    assert_eq!(size_of::<T::Assoc>(), 1);
+    assert_eq!(T::CONST, 1);
+}
diff --git a/tests/ui/methods/supertrait-shadowing/trivially-false-subtrait.rs b/tests/ui/supertrait-shadowing/trivially-false-subtrait.rs
similarity index 100%
rename from tests/ui/methods/supertrait-shadowing/trivially-false-subtrait.rs
rename to tests/ui/supertrait-shadowing/trivially-false-subtrait.rs
diff --git a/tests/ui/supertrait-shadowing/type-dependent.rs b/tests/ui/supertrait-shadowing/type-dependent.rs
new file mode 100644
index 0000000000000..75272d101dd29
--- /dev/null
+++ b/tests/ui/supertrait-shadowing/type-dependent.rs
@@ -0,0 +1,51 @@
+//@ run-pass
+
+// Makes sure we can shadow with type-dependent associated item syntax.
+
+#![feature(min_generic_const_args)]
+#![feature(supertrait_item_shadowing)]
+#![allow(dead_code)]
+
+use std::mem::size_of;
+
+trait A {
+    fn hello() -> &'static str {
+        "A"
+    }
+    type Assoc;
+    const CONST: i32;
+}
+impl<T> A for T {
+    type Assoc = i8;
+    const CONST: i32 = 1;
+}
+
+trait B: A {
+    fn hello() -> &'static str {
+        "B"
+    }
+    type Assoc;
+    type const CONST: i32;
+}
+impl<T> B for T {
+    type Assoc = i16;
+    type const CONST: i32 = 2;
+}
+
+fn foo<T>() -> &'static str {
+    T::hello()
+}
+
+fn assoc<T: B>() -> usize {
+    size_of::<T::Assoc>()
+}
+
+fn konst<T: B>() -> i32 {
+    T::CONST
+}
+
+fn main() {
+    assert_eq!(foo::<()>(), "B");
+    assert_eq!(assoc::<()>(), 2);
+    assert_eq!(konst::<()>(), 2);
+}
diff --git a/tests/ui/methods/supertrait-shadowing/unstable.off_normal.stderr b/tests/ui/supertrait-shadowing/unstable.off_normal.stderr
similarity index 100%
rename from tests/ui/methods/supertrait-shadowing/unstable.off_normal.stderr
rename to tests/ui/supertrait-shadowing/unstable.off_normal.stderr
diff --git a/tests/ui/methods/supertrait-shadowing/unstable.off_shadowing.stderr b/tests/ui/supertrait-shadowing/unstable.off_shadowing.stderr
similarity index 100%
rename from tests/ui/methods/supertrait-shadowing/unstable.off_shadowing.stderr
rename to tests/ui/supertrait-shadowing/unstable.off_shadowing.stderr
diff --git a/tests/ui/methods/supertrait-shadowing/unstable.on_normal.stderr b/tests/ui/supertrait-shadowing/unstable.on_normal.stderr
similarity index 100%
rename from tests/ui/methods/supertrait-shadowing/unstable.on_normal.stderr
rename to tests/ui/supertrait-shadowing/unstable.on_normal.stderr
diff --git a/tests/ui/methods/supertrait-shadowing/unstable.rs b/tests/ui/supertrait-shadowing/unstable.rs
similarity index 100%
rename from tests/ui/methods/supertrait-shadowing/unstable.rs
rename to tests/ui/supertrait-shadowing/unstable.rs