Rollup merge of rust-lang#62696 - chocol4te:fix_#62194, r=estebank

Check that trait is exported or public before adding hint

Closes rust-lang#62194.

This PR checks the `AccessLevels` of a trait to check whether adding the intercrate ambiguity hint is valid or not.

I am unsure of both the use of `.unwrap()` as well as removing hints for [downstream *and* [upstream](https://github.com/rust-lang/rust/blob/92b0f52584c9375505ecdefdd7855b93a5919d51/src/librustc/traits/select.rs#L112-L142).

Author: Mark-Simulacrum

src/librustc/traits/specialize/mod.rs

@@ -366,8 +366,13 @@ pub(super) fn specialization_graph_provider(
                     }
                 }
 
-                for cause in &overlap.intercrate_ambiguity_causes {
-                    cause.add_intercrate_ambiguity_hint(&mut err);
+                let access_levels = tcx.privacy_access_levels(impl_def_id.krate);
+                if let Some(id) = tcx.hir().as_local_hir_id(impl_def_id) {
+                    if access_levels.is_exported(id) || access_levels.is_public(id) {
+                        for cause in &overlap.intercrate_ambiguity_causes {
+                            cause.add_intercrate_ambiguity_hint(&mut err);
+                        }
+                    }
                 }
 
                 if overlap.involves_placeholder {

src/test/ui/coherence/coherence-overlap-upstream.old.stderr

@@ -5,8 +5,6 @@ LL | impl<T> Foo for T where T: Remote {}
    | --------------------------------- first implementation here
 LL | impl Foo for i16 {}
    | ^^^^^^^^^^^^^^^^ conflicting implementation for `i16`
-   |
-   = note: upstream crates may add new impl of trait `coherence_lib::Remote` for type `i16` in future versions
 
 error: aborting due to previous error
 

src/test/ui/coherence/coherence-overlap-upstream.re.stderr

@@ -5,8 +5,6 @@ LL | impl<T> Foo for T where T: Remote {}
    | --------------------------------- first implementation here
 LL | impl Foo for i16 {}
    | ^^^^^^^^^^^^^^^^ conflicting implementation for `i16`
-   |
-   = note: upstream crates may add new impl of trait `coherence_lib::Remote` for type `i16` in future versions
 
 error: aborting due to previous error
 

src/test/ui/coherence/coherence_copy_like_err_fundamental_struct_tuple.old.stderr

@@ -6,8 +6,6 @@ LL | impl<T: lib::MyCopy> MyTrait for T { }
 ...
 LL | impl MyTrait for lib::MyFundamentalStruct<(MyType,)> { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `lib::MyFundamentalStruct<(MyType,)>`
-   |
-   = note: upstream crates may add new impl of trait `lib::MyCopy` for type `lib::MyFundamentalStruct<(MyType,)>` in future versions
 
 error: aborting due to previous error
 

src/test/ui/coherence/coherence_copy_like_err_fundamental_struct_tuple.re.stderr

@@ -6,8 +6,6 @@ LL | impl<T: lib::MyCopy> MyTrait for T { }
 ...
 LL | impl MyTrait for lib::MyFundamentalStruct<(MyType,)> { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `lib::MyFundamentalStruct<(MyType,)>`
-   |
-   = note: upstream crates may add new impl of trait `lib::MyCopy` for type `lib::MyFundamentalStruct<(MyType,)>` in future versions
 
 error: aborting due to previous error
 

src/test/ui/coherence/coherence_copy_like_err_struct.old.stderr

@@ -6,8 +6,6 @@ LL | impl<T: lib::MyCopy> MyTrait for T { }
 ...
 LL | impl MyTrait for lib::MyStruct<MyType> { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `lib::MyStruct<MyType>`
-   |
-   = note: upstream crates may add new impl of trait `lib::MyCopy` for type `lib::MyStruct<MyType>` in future versions
 
 error: aborting due to previous error
 

src/test/ui/coherence/coherence_copy_like_err_struct.re.stderr

@@ -6,8 +6,6 @@ LL | impl<T: lib::MyCopy> MyTrait for T { }
 ...
 LL | impl MyTrait for lib::MyStruct<MyType> { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `lib::MyStruct<MyType>`
-   |
-   = note: upstream crates may add new impl of trait `lib::MyCopy` for type `lib::MyStruct<MyType>` in future versions
 
 error: aborting due to previous error
 

src/test/ui/coherence/coherence_copy_like_err_tuple.old.stderr

@@ -6,8 +6,6 @@ LL | impl<T: lib::MyCopy> MyTrait for T { }
 ...
 LL | impl MyTrait for (MyType,) { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(MyType,)`
-   |
-   = note: upstream crates may add new impl of trait `lib::MyCopy` for type `(MyType,)` in future versions
 
 error: aborting due to previous error
 

src/test/ui/coherence/coherence_copy_like_err_tuple.re.stderr

@@ -6,8 +6,6 @@ LL | impl<T: lib::MyCopy> MyTrait for T { }
 ...
 LL | impl MyTrait for (MyType,) { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(MyType,)`
-   |
-   = note: upstream crates may add new impl of trait `lib::MyCopy` for type `(MyType,)` in future versions
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-48728.stderr

@@ -6,8 +6,6 @@ LL | #[derive(Clone)]
 ...
 LL | impl<T: Clone + ?Sized> Clone for Node<[T]> {
    | ------------------------------------------- first implementation here
-   |
-   = note: upstream crates may add new impl of trait `std::clone::Clone` for type `[_]` in future versions
 
 error: aborting due to previous error
 

src/test/ui/specialization/issue-52050.stderr

@@ -10,8 +10,6 @@ LL | | }
 LL | 
 LL |   impl IntoPyDictPointer for ()
    |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `()`
-   |
-   = note: upstream crates may add new impl of trait `std::iter::Iterator` for type `()` in future versions
 
 error: aborting due to previous error