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

Skip possible where_clause_object_safety lints when checking `multiple_supertrait_upcastable`

Fix #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`

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -361,7 +361,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
     }
 
     fn compute_object_safe_goal(&mut self, trait_def_id: DefId) -> QueryResult<'tcx> {
-        if self.tcx().is_object_safe(trait_def_id) {
+        if self.tcx().check_is_object_safe(trait_def_id) {
             self.make_canonical_response(Certainty::Yes)
         } else {
             Err(NoSolution)

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

@@ -1748,7 +1748,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 // If the `dyn Trait` is not object safe, do not suggest `Box<dyn Trait>`.
                 predicates
                     .principal_def_id()
-                    .map_or(true, |def_id| self.tcx.object_safety_violations(def_id).is_empty())
+                    .map_or(true, |def_id| self.tcx.check_is_object_safe(def_id))
             }
             // We only want to suggest `impl Trait` to `dyn Trait`s.
             // For example, `fn foo() -> str` needs to be filtered out.

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -369,7 +369,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 }
 
                 ty::PredicateKind::ObjectSafe(trait_def_id) => {
-                    if !self.selcx.tcx().is_object_safe(trait_def_id) {
+                    if !self.selcx.tcx().check_is_object_safe(trait_def_id) {
                         ProcessResult::Error(CodeSelectionError(Unimplemented))
                     } else {
                         ProcessResult::Changed(vec![])

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -62,6 +62,37 @@ fn object_safety_violations(tcx: TyCtxt<'_>, trait_def_id: DefId) -> &'_ [Object
     )
 }
 
+fn check_is_object_safe(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool {
+    let violations = tcx.object_safety_violations(trait_def_id);
+
+    if violations.is_empty() {
+        return true;
+    }
+
+    // If the trait contains any other violations, then let the error reporting path
+    // report it instead of emitting a warning here.
+    if violations.iter().all(|violation| {
+        matches!(
+            violation,
+            ObjectSafetyViolation::Method(_, MethodViolationCode::WhereClauseReferencesSelf, _)
+        )
+    }) {
+        for violation in violations {
+            if let ObjectSafetyViolation::Method(
+                _,
+                MethodViolationCode::WhereClauseReferencesSelf,
+                span,
+            ) = violation
+            {
+                lint_object_unsafe_trait(tcx, *span, trait_def_id, &violation);
+            }
+        }
+        return true;
+    }
+
+    false
+}
+
 /// We say a method is *vtable safe* if it can be invoked on a trait
 /// object. Note that object-safe traits can have some
 /// non-vtable-safe methods, so long as they require `Self: Sized` or
@@ -93,19 +124,6 @@ fn object_safety_violations_for_trait(
             object_safety_violation_for_method(tcx, trait_def_id, &item)
                 .map(|(code, span)| ObjectSafetyViolation::Method(item.name, code, span))
         })
-        .filter(|violation| {
-            if let ObjectSafetyViolation::Method(
-                _,
-                MethodViolationCode::WhereClauseReferencesSelf,
-                span,
-            ) = violation
-            {
-                lint_object_unsafe_trait(tcx, *span, trait_def_id, &violation);
-                false
-            } else {
-                true
-            }
-        })
         .collect();
 
     // Check the trait itself.
@@ -866,5 +884,6 @@ pub fn contains_illegal_impl_trait_in_trait<'tcx>(
 }
 
 pub fn provide(providers: &mut ty::query::Providers) {
-    *providers = ty::query::Providers { object_safety_violations, ..*providers };
+    *providers =
+        ty::query::Providers { object_safety_violations, check_is_object_safe, ..*providers };
 }

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -466,7 +466,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     if let Some(principal) = data.principal() {
                         if !self.infcx.tcx.features().object_safe_for_dispatch {
                             principal.with_self_ty(self.tcx(), self_ty)
-                        } else if self.tcx().is_object_safe(principal.def_id()) {
+                        } else if self.tcx().check_is_object_safe(principal.def_id()) {
                             principal.with_self_ty(self.tcx(), self_ty)
                         } else {
                             return;

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -1009,7 +1009,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             // `T` -> `Trait`
             (_, &ty::Dynamic(ref data, r, ty::Dyn)) => {
                 let mut object_dids = data.auto_traits().chain(data.principal_def_id());
-                if let Some(did) = object_dids.find(|did| !tcx.is_object_safe(*did)) {
+                if let Some(did) = object_dids.find(|did| !tcx.check_is_object_safe(*did)) {
                     return Err(TraitNotObjectSafe(did));
                 }
 

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

@@ -797,7 +797,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
 
                 ty::PredicateKind::ObjectSafe(trait_def_id) => {
-                    if self.tcx().is_object_safe(trait_def_id) {
+                    if self.tcx().check_is_object_safe(trait_def_id) {
                         Ok(EvaluatedToOk)
                     } else {
                         Ok(EvaluatedToErr)