Auto merge of rust-lang#106253 - nbdd0121:upcast, r=compiler-errors

Skip possible where_clause_object_safety lints when checking `multiple_supertrait_upcastable`

Fix rust-lang#106247

To achieve this, I lifted the `WhereClauseReferencesSelf` out from `object_safety_violations` and move it into `is_object_safe` (which is changed to a new query).

cc `@dtolnay`
r? `@compiler-errors`

Author: bors

alloc/src/lib.rs

@@ -87,6 +87,7 @@
 #![warn(missing_debug_implementations)]
 #![warn(missing_docs)]
 #![allow(explicit_outlives_requirements)]
+#![cfg_attr(not(bootstrap), warn(multiple_supertrait_upcastable))]
 //
 // Library features:
 #![feature(alloc_layout_extra)]
@@ -195,6 +196,7 @@
 #![feature(c_unwind)]
 #![feature(with_negative_coherence)]
 #![cfg_attr(test, feature(panic_update_hook))]
+#![cfg_attr(not(bootstrap), feature(multiple_supertrait_upcastable))]
 //
 // Rustdoc features:
 #![feature(doc_cfg)]

core/src/error.rs

@@ -28,6 +28,7 @@ use crate::fmt::{Debug, Display};
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "Error")]
 #[rustc_has_incoherent_inherent_impls]
+#[cfg_attr(not(bootstrap), allow(multiple_supertrait_upcastable))]
 pub trait Error: Debug + Display {
     /// The lower-level source of this error, if any.
     ///

core/src/lib.rs

@@ -95,6 +95,7 @@
 #![warn(missing_docs)]
 #![allow(explicit_outlives_requirements)]
 #![allow(incomplete_features)]
+#![cfg_attr(not(bootstrap), warn(multiple_supertrait_upcastable))]
 //
 // Library features:
 #![feature(const_align_offset)]
@@ -235,6 +236,7 @@
 #![feature(unsized_fn_params)]
 #![feature(asm_const)]
 #![feature(const_transmute_copy)]
+#![cfg_attr(not(bootstrap), feature(multiple_supertrait_upcastable))]
 //
 // Target features:
 #![feature(arm_target_feature)]