Don't try to label ObligationCauseCode::CompareImplItem for an RPITIT, since it has no name

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

@@ -3472,6 +3472,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     )
                 });
             }
+            // Suppress `compare_type_predicate_entailment` errors for RPITITs, since they
+            // should be implied by the parent method.
+            ObligationCauseCode::CompareImplItem { trait_item_def_id, .. }
+                if tcx.is_impl_trait_in_trait(trait_item_def_id) => {}
             ObligationCauseCode::CompareImplItem { trait_item_def_id, kind, .. } => {
                 let item_name = tcx.item_name(trait_item_def_id);
                 let msg = format!(

tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.current.stderr

@@ -0,0 +1,173 @@
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:5
+   |
+LL | /     fn autobatch<F>(self) -> impl Trait
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     where
+LL | |         F: Callback<Self::CallbackArg>,
+   | |_______________________________________^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:30
+   |
+LL |     fn autobatch<F>(self) -> impl Trait
+   |                              ^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+note: required by a bound in `<Sender as ChannelSender>::autobatch`
+  --> $DIR/false-positive-predicate-entailment-error.rs:43:12
+   |
+LL |     fn autobatch<F>(self) -> impl Trait
+   |        --------- required by a bound in this associated function
+...
+LL |         F: Callback<Self::CallbackArg>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `<Sender as ChannelSender>::autobatch`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:5
+   |
+LL | /     fn autobatch<F>(self) -> impl Trait
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     where
+LL | |         F: Callback<Self::CallbackArg>,
+   | |_______________________________________^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: Callback<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:43:12
+   |
+LL |         F: Callback<Self::CallbackArg>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+note: the requirement `F: Callback<i32>` appears on the `impl`'s method `autobatch` but not on the corresponding trait's method
+  --> $DIR/false-positive-predicate-entailment-error.rs:25:8
+   |
+LL | trait ChannelSender {
+   |       ------------- in this trait
+...
+LL |     fn autobatch<F>(self) -> impl Trait
+   |        ^^^^^^^^^ this trait's method doesn't have the requirement `F: Callback<i32>`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:30
+   |
+LL |     fn autobatch<F>(self) -> impl Trait
+   |                              ^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+
+error[E0277]: the trait bound `F: Callback<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:27:12
+   |
+LL |         F: Callback<Self::CallbackArg>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:36:5
+   |
+LL | /     fn autobatch<F>(self) -> impl Trait
+LL | |
+LL | |
+LL | |
+...  |
+LL | |     where
+LL | |         F: Callback<Self::CallbackArg>,
+   | |_______________________________________^ the trait `MyFn<i32>` is not implemented for `F`, which is required by `F: Callback<i32>`
+   |
+note: required for `F` to implement `Callback<i32>`
+  --> $DIR/false-positive-predicate-entailment-error.rs:14:21
+   |
+LL | impl<A, F: MyFn<A>> Callback<A> for F {
+   |            -------  ^^^^^^^^^^^     ^
+   |            |
+   |            unsatisfied trait bound introduced here
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error[E0277]: the trait bound `F: MyFn<i32>` is not satisfied
+  --> $DIR/false-positive-predicate-entailment-error.rs:43:12
+   |
+LL |         F: Callback<Self::CallbackArg>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MyFn<i32>` is not implemented for `F`
+   |
+note: required by a bound in `Callback`
+  --> $DIR/false-positive-predicate-entailment-error.rs:10:20
+   |
+LL | trait Callback<A>: MyFn<A, Output = Self::Ret> {
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Callback`
+help: consider further restricting this bound
+   |
+LL |         F: Callback<Self::CallbackArg> + MyFn<i32>,
+   |                                        +++++++++++
+
+error: aborting due to 8 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/impl-trait/in-trait/false-positive-predicate-entailment-error.rs

@@ -0,0 +1,51 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
+trait MyFn<T> {
+    type Output;
+}
+
+trait Callback<A>: MyFn<A, Output = Self::Ret> {
+    type Ret;
+}
+
+impl<A, F: MyFn<A>> Callback<A> for F {
+    type Ret = F::Output;
+}
+
+struct Thing;
+trait Trait {}
+impl Trait for Thing {}
+
+trait ChannelSender {
+    type CallbackArg;
+
+    fn autobatch<F>(self) -> impl Trait
+    where
+        F: Callback<Self::CallbackArg>;
+        //[current]~^ ERROR the trait bound `F: Callback<i32>` is not satisfied
+}
+
+struct Sender;
+
+impl ChannelSender for Sender {
+    type CallbackArg = i32;
+
+    fn autobatch<F>(self) -> impl Trait
+    //[current]~^ ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    where
+        F: Callback<Self::CallbackArg>,
+        //[current]~^ ERROR the trait bound `F: Callback<i32>` is not satisfied
+        //[current]~| ERROR the trait bound `F: MyFn<i32>` is not satisfied
+    {
+        Thing
+    }
+}
+
+fn main() {}