add tests

compiler/rustc_infer/src/infer/generalize.rs

@@ -343,7 +343,7 @@ where
                                 self.for_universe.can_name(visitor.max_universe())
                                     && !t.has_escaping_bound_vars();
                             if !infer_replacement_is_complete {
-                                warn!("incomplete generalization of an alias type: {t:?}");
+                                warn!("may incompletely handle alias type: {t:?}");
                             }
 
                             debug!("generalization failure in alias");

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -930,7 +930,13 @@ impl<'a, 'tcx> ProofTreeVisitor<'tcx> for AmbiguityCausesVisitor<'a> {
         let trait_ref = match predicate.kind().no_bound_vars() {
             Some(ty::PredicateKind::Clause(ty::ClauseKind::Trait(tr))) => tr.trait_ref,
             Some(ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj))) => {
-                proj.projection_ty.trait_ref(infcx.tcx)
+                match proj.projection_ty.kind(infcx.tcx) {
+                    ty::AliasKind::Projection => proj.projection_ty.trait_ref(infcx.tcx),
+                    ty::AliasKind::Inherent | ty::AliasKind::Opaque | ty::AliasKind::Weak => {
+                        // No intercrate ambiguity causes here.
+                        return ControlFlow::Continue(());
+                    }
+                }
             }
             _ => return ControlFlow::Continue(()),
         };

tests/ui/coherence/occurs-check/associated-type.next.stderr

@@ -0,0 +1,25 @@
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, RePlaceholder(!2_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, RePlaceholder(!2_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, RePlaceholder(!2_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, RePlaceholder(!2_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+error[E0119]: conflicting implementations of trait `Overlap<for<'a> fn(&'a (), ())>` for type `for<'a> fn(&'a (), ())`
+  --> $DIR/associated-type.rs:31:1
+   |
+LL |   impl<T> Overlap<T> for T {
+   |   ------------------------ first implementation here
+...
+LL | / impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T
+LL | |
+LL | | where
+LL | |     for<'a> *const T: ToUnit<'a>,
+   | |_________________________________^ conflicting implementation for `for<'a> fn(&'a (), ())`
+   |
+   = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/occurs-check/associated-type.old.stderr

@@ -0,0 +1,25 @@
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, RePlaceholder(!3_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, RePlaceholder(!3_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, RePlaceholder(!3_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+WARN rustc_infer::infer::generalize may incompletely handle alias type: Alias(Projection, AliasTy { args: [*const ?1t, RePlaceholder(!3_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) })
+error[E0119]: conflicting implementations of trait `Overlap<for<'a> fn(&'a (), _)>` for type `for<'a> fn(&'a (), _)`
+  --> $DIR/associated-type.rs:31:1
+   |
+LL |   impl<T> Overlap<T> for T {
+   |   ------------------------ first implementation here
+...
+LL | / impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T
+LL | |
+LL | | where
+LL | |     for<'a> *const T: ToUnit<'a>,
+   | |_________________________________^ conflicting implementation for `for<'a> fn(&'a (), _)`
+   |
+   = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/occurs-check/associated-type.rs

@@ -0,0 +1,45 @@
+// revisions: old next
+//[next] compile-flags: -Ztrait-solver=next
+
+// A regression test for #105787
+
+// Using the higher ranked projection hack to prevent us from replacing the projection
+// with an inference variable.
+trait ToUnit<'a> {
+    type Unit;
+}
+
+struct LocalTy;
+impl<'a> ToUnit<'a> for *const LocalTy {
+    type Unit = ();
+}
+
+impl<'a, T: Copy + ?Sized> ToUnit<'a> for *const T {
+    type Unit = ();
+}
+
+trait Overlap<T> {
+    type Assoc;
+}
+
+type Assoc<'a, T> = <*const T as ToUnit<'a>>::Unit;
+
+impl<T> Overlap<T> for T {
+    type Assoc = usize;
+}
+
+impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T
+//~^ ERROR conflicting implementations of trait
+where
+    for<'a> *const T: ToUnit<'a>,
+{
+    type Assoc = Box<usize>;
+}
+
+fn foo<T: Overlap<U>, U>(x: T::Assoc) -> T::Assoc {
+    x
+}
+
+fn main() {
+    foo::<for<'a> fn(&'a (), ()), for<'a> fn(&'a (), ())>(3usize);
+}

tests/ui/coherence/occurs-check/opaques.next.stderr

@@ -0,0 +1,12 @@
+error[E0119]: conflicting implementations of trait `Trait<Alias<_>>` for type `Alias<_>`
+  --> $DIR/opaques.rs:29:1
+   |
+LL | impl<T> Trait<T> for T {
+   | ---------------------- first implementation here
+...
+LL | impl<T> Trait<T> for defining_scope::Alias<T> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Alias<_>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/occurs-check/opaques.rs

@@ -0,0 +1,37 @@
+//revisions: old next
+//[next] compile-flags: -Ztrait-solver=next
+
+// A regression test for #105787
+
+//[old] known-bug: #105787
+//[old] check-pass
+#![feature(type_alias_impl_trait)]
+mod defining_scope {
+    use super::*;
+    pub type Alias<T> = impl Sized;
+
+    pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
+        x
+    }
+}
+
+struct Container<T: Trait<U>, U> {
+    x: <T as Trait<U>>::Assoc,
+}
+
+trait Trait<T> {
+    type Assoc;
+}
+
+impl<T> Trait<T> for T {
+    type Assoc = Box<u32>;
+}
+impl<T> Trait<T> for defining_scope::Alias<T> {
+    //[next]~^ ERROR conflicting implementations of trait
+    type Assoc = usize;
+}
+
+fn main() {
+    let x: Box<u32> = defining_scope::cast::<()>(Container { x: 0 }).x;
+    println!("{}", *x);
+}