Rollup merge of #121386 - oli-obk:no_higher_ranked_opaques, r=lcnr

test that we do not support higher-ranked regions in opaque type inference

We already do all the right checks in `check_opaque_type_parameter_valid`, and we have done so since at least 2 years.

I collected the tests from #116935 and #100503 and added some more

cc #96146

r? `@lcnr`

Author: matthiaskrgr

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -153,12 +153,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             if let Some(prev) = result.get_mut(&opaque_type_key.def_id) {
                 if prev.ty != ty {
                     let guar = ty.error_reported().err().unwrap_or_else(|| {
-                        prev.report_mismatch(
-                            &OpaqueHiddenType { ty, span: concrete_type.span },
-                            opaque_type_key.def_id,
-                            infcx.tcx,
-                        )
-                        .emit()
+                        let (Ok(e) | Err(e)) = prev
+                            .build_mismatch_error(
+                                &OpaqueHiddenType { ty, span: concrete_type.span },
+                                opaque_type_key.def_id,
+                                infcx.tcx,
+                            )
+                            .map(|d| d.emit());
+                        e
                     });
                     prev.ty = Ty::new_error(infcx.tcx, guar);
                 }

compiler/rustc_hir_analysis/src/check/check.rs

@@ -477,7 +477,7 @@ fn sanity_check_found_hidden_type<'tcx>(
     } else {
         let span = tcx.def_span(key.def_id);
         let other = ty::OpaqueHiddenType { ty: hidden_ty, span };
-        Err(ty.report_mismatch(&other, key.def_id, tcx).emit())
+        Err(ty.build_mismatch_error(&other, key.def_id, tcx)?.emit())
     }
 }
 

compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs

@@ -58,10 +58,10 @@ pub(super) fn find_opaque_ty_constraints_for_impl_trait_in_assoc_type(
         // Only check against typeck if we didn't already error
         if !hidden.ty.references_error() {
             for concrete_type in locator.typeck_types {
-                if concrete_type.ty != tcx.erase_regions(hidden.ty)
-                    && !(concrete_type, hidden).references_error()
-                {
-                    hidden.report_mismatch(&concrete_type, def_id, tcx).emit();
+                if concrete_type.ty != tcx.erase_regions(hidden.ty) {
+                    if let Ok(d) = hidden.build_mismatch_error(&concrete_type, def_id, tcx) {
+                        d.emit();
+                    }
                 }
             }
         }
@@ -134,10 +134,10 @@ pub(super) fn find_opaque_ty_constraints_for_tait(tcx: TyCtxt<'_>, def_id: Local
         // Only check against typeck if we didn't already error
         if !hidden.ty.references_error() {
             for concrete_type in locator.typeck_types {
-                if concrete_type.ty != tcx.erase_regions(hidden.ty)
-                    && !(concrete_type, hidden).references_error()
-                {
-                    hidden.report_mismatch(&concrete_type, def_id, tcx).emit();
+                if concrete_type.ty != tcx.erase_regions(hidden.ty) {
+                    if let Ok(d) = hidden.build_mismatch_error(&concrete_type, def_id, tcx) {
+                        d.emit();
+                    }
                 }
             }
         }
@@ -287,8 +287,10 @@ impl TaitConstraintLocator<'_> {
         if let Some(&concrete_type) = borrowck_results.concrete_opaque_types.get(&self.def_id) {
             debug!(?concrete_type, "found constraint");
             if let Some(prev) = &mut self.found {
-                if concrete_type.ty != prev.ty && !(concrete_type, prev.ty).references_error() {
-                    let guar = prev.report_mismatch(&concrete_type, self.def_id, self.tcx).emit();
+                if concrete_type.ty != prev.ty {
+                    let (Ok(guar) | Err(guar)) = prev
+                        .build_mismatch_error(&concrete_type, self.def_id, self.tcx)
+                        .map(|d| d.emit());
                     prev.ty = Ty::new_error(self.tcx, guar);
                 }
             } else {
@@ -361,11 +363,13 @@ pub(super) fn find_opaque_ty_constraints_for_rpit<'tcx>(
                 hidden_type.remap_generic_params_to_declaration_params(opaque_type_key, tcx, true),
             );
             if let Some(prev) = &mut hir_opaque_ty {
-                if concrete_type.ty != prev.ty && !(concrete_type, prev.ty).references_error() {
-                    prev.report_mismatch(&concrete_type, def_id, tcx).stash(
-                        tcx.def_span(opaque_type_key.def_id),
-                        StashKey::OpaqueHiddenTypeMismatch,
-                    );
+                if concrete_type.ty != prev.ty {
+                    if let Ok(d) = prev.build_mismatch_error(&concrete_type, def_id, tcx) {
+                        d.stash(
+                            tcx.def_span(opaque_type_key.def_id),
+                            StashKey::OpaqueHiddenTypeMismatch,
+                        );
+                    }
                 }
             } else {
                 hir_opaque_ty = Some(concrete_type);
@@ -436,9 +440,12 @@ impl RpitConstraintChecker<'_> {
 
             debug!(?concrete_type, "found constraint");
 
-            if concrete_type.ty != self.found.ty && !(concrete_type, self.found).references_error()
-            {
-                self.found.report_mismatch(&concrete_type, self.def_id, self.tcx).emit();
+            if concrete_type.ty != self.found.ty {
+                if let Ok(d) =
+                    self.found.build_mismatch_error(&concrete_type, self.def_id, self.tcx)
+                {
+                    d.emit();
+                }
             }
         }
     }

compiler/rustc_hir_typeck/src/writeback.rs

@@ -589,12 +589,16 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
                 && last_opaque_ty.ty != hidden_type.ty
             {
                 assert!(!self.fcx.next_trait_solver());
-                hidden_type
-                    .report_mismatch(&last_opaque_ty, opaque_type_key.def_id, self.tcx())
-                    .stash(
+                if let Ok(d) = hidden_type.build_mismatch_error(
+                    &last_opaque_ty,
+                    opaque_type_key.def_id,
+                    self.tcx(),
+                ) {
+                    d.stash(
                         self.tcx().def_span(opaque_type_key.def_id),
                         StashKey::OpaqueHiddenTypeMismatch,
                     );
+                }
             }
         }
     }

compiler/rustc_middle/src/ty/mod.rs

@@ -840,31 +840,32 @@ pub struct OpaqueHiddenType<'tcx> {
 }
 
 impl<'tcx> OpaqueHiddenType<'tcx> {
-    pub fn report_mismatch(
+    pub fn build_mismatch_error(
         &self,
         other: &Self,
         opaque_def_id: LocalDefId,
         tcx: TyCtxt<'tcx>,
-    ) -> DiagnosticBuilder<'tcx> {
+    ) -> Result<DiagnosticBuilder<'tcx>, ErrorGuaranteed> {
         if let Some(diag) = tcx
             .sess
             .dcx()
             .steal_diagnostic(tcx.def_span(opaque_def_id), StashKey::OpaqueHiddenTypeMismatch)
         {
             diag.cancel();
         }
+        (self.ty, other.ty).error_reported()?;
         // Found different concrete types for the opaque type.
         let sub_diag = if self.span == other.span {
             TypeMismatchReason::ConflictType { span: self.span }
         } else {
             TypeMismatchReason::PreviousUse { span: self.span }
         };
-        tcx.dcx().create_err(OpaqueHiddenTypeMismatch {
+        Ok(tcx.dcx().create_err(OpaqueHiddenTypeMismatch {
             self_ty: self.ty,
             other_ty: other.ty,
             other_span: other.span,
             sub: sub_diag,
-        })
+        }))
     }
 
     #[instrument(level = "debug", skip(tcx), ret)]

compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs

@@ -98,6 +98,7 @@ pub trait QueryTypeOp<'tcx>: fmt::Debug + Copy + TypeFoldable<TyCtxt<'tcx>> + 't
         query_key: ParamEnvAnd<'tcx, Self>,
         infcx: &InferCtxt<'tcx>,
         output_query_region_constraints: &mut QueryRegionConstraints<'tcx>,
+        span: Span,
     ) -> Result<
         (
             Self::QueryResponse,
@@ -118,7 +119,7 @@ pub trait QueryTypeOp<'tcx>: fmt::Debug + Copy + TypeFoldable<TyCtxt<'tcx>> + 't
 
         let InferOk { value, obligations } = infcx
             .instantiate_nll_query_response_and_region_obligations(
-                &ObligationCause::dummy(),
+                &ObligationCause::dummy_with_span(span),
                 old_param_env,
                 &canonical_var_values,
                 canonical_result,
@@ -160,7 +161,7 @@ where
 
         let mut region_constraints = QueryRegionConstraints::default();
         let (output, error_info, mut obligations, _) =
-            Q::fully_perform_into(self, infcx, &mut region_constraints).map_err(|_| {
+            Q::fully_perform_into(self, infcx, &mut region_constraints, span).map_err(|_| {
                 infcx.dcx().span_delayed_bug(span, format!("error performing {self:?}"))
             })?;
 
@@ -178,6 +179,7 @@ where
                     obligation.param_env.and(ProvePredicate::new(obligation.predicate)),
                     infcx,
                     &mut region_constraints,
+                    span,
                 ) {
                     Ok(((), _, new, certainty)) => {
                         obligations.extend(new);

tests/ui/generic-associated-types/issue-90014-tait2.stderr

@@ -1,4 +1,11 @@
 error[E0792]: expected generic lifetime parameter, found `'a`
+  --> $DIR/issue-90014-tait2.rs:27:9
+   |
+LL | type Fut<'a> = impl Future<Output = ()>;
+   |          -- this generic parameter must be used with a generic lifetime parameter
+...
+LL |         Box::new((async { () },))
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 

tests/ui/rfcs/impl-trait/higher-ranked-regions-diag.rs

@@ -0,0 +1,23 @@
+// Regression test for #97099.
+// This was an ICE because `impl Sized` captures the lifetime 'a.
+
+trait Trait<E> {
+    type Assoc;
+}
+
+struct Foo;
+
+impl<'a> Trait<&'a ()> for Foo {
+    type Assoc = ();
+}
+
+fn foo() -> impl for<'a> Trait<&'a ()> {
+    Foo
+}
+
+fn bar() -> impl for<'a> Trait<&'a (), Assoc = impl Sized> {
+    foo()
+    //~^ ERROR hidden type for `impl Sized` captures lifetime that does not appear in bounds
+}
+
+fn main() {}

tests/ui/rfcs/impl-trait/higher-ranked-regions-diag.stderr

@@ -0,0 +1,13 @@
+error[E0700]: hidden type for `impl Sized` captures lifetime that does not appear in bounds
+  --> $DIR/higher-ranked-regions-diag.rs:19:5
+   |
+LL | fn bar() -> impl for<'a> Trait<&'a (), Assoc = impl Sized> {
+   |                      --                        ---------- opaque type defined here
+   |                      |
+   |                      hidden type `<impl for<'a> Trait<&'a ()> as Trait<&'a ()>>::Assoc` captures the lifetime `'a` as defined here
+LL |     foo()
+   |     ^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0700`.

tests/ui/rfcs/type-alias-impl-trait/higher-ranked-regions-basic.rs

@@ -0,0 +1,80 @@
+// Basic tests for opaque type inference under for<_> binders.
+
+#![feature(type_alias_impl_trait)]
+
+trait Trait<'a> {
+    type Ty;
+}
+impl<'a, T> Trait<'a> for T {
+    type Ty = &'a ();
+}
+
+mod basic_pass {
+    use super::*;
+    type Opq<'a> = impl Sized + 'a;
+    fn test() -> impl for<'a> Trait<'a, Ty = Opq<'a>> {}
+    //~^ ERROR: expected generic lifetime parameter, found `'a`
+}
+
+mod capture_rpit {
+    use super::*;
+    fn test() -> impl for<'a> Trait<'a, Ty = impl Sized> {}
+    //~^ ERROR hidden type for `impl Sized` captures lifetime that does not appear in bounds
+}
+
+mod capture_tait {
+    use super::*;
+    type Opq0 = impl Sized;
+    type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0>;
+    type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+    fn test() -> Opq2 {}
+    //~^ ERROR hidden type for `capture_tait::Opq0` captures lifetime that does not appear in bounds
+}
+
+mod capture_tait_complex_pass {
+    use super::*;
+    type Opq0<'a> = impl Sized;
+    type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'b>>; // <- Note 'b
+    type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+    fn test() -> Opq2 {}
+    //~^ ERROR: expected generic lifetime parameter, found `'a`
+}
+
+// Same as the above, but make sure that different placeholder regions are not equal.
+mod capture_tait_complex_fail {
+    use super::*;
+    type Opq0<'a> = impl Sized;
+    type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'a>>; // <- Note 'a
+    type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+    fn test() -> Opq2 {}
+    //~^ ERROR hidden type for `capture_tait_complex_fail::Opq0<'a>` captures lifetime that does not appear in bounds
+}
+
+// non-defining use because 'static is used.
+mod constrain_fail0 {
+    use super::*;
+    type Opq0<'a, 'b> = impl Sized;
+    fn test() -> impl for<'a> Trait<'a, Ty = Opq0<'a, 'static>> {}
+    //~^ ERROR non-defining opaque type use in defining scope
+    //~| ERROR: expected generic lifetime parameter, found `'a`
+}
+
+// non-defining use because generic lifetime is used multiple times.
+mod constrain_fail {
+    use super::*;
+    type Opq0<'a, 'b> = impl Sized;
+    fn test() -> impl for<'a> Trait<'a, Ty = Opq0<'a, 'a>> {}
+    //~^ ERROR non-defining opaque type use in defining scope
+    //~| ERROR: expected generic lifetime parameter, found `'a`
+}
+
+mod constrain_pass {
+    use super::*;
+    type Opq0<'a, 'b> = impl Sized;
+    type Opq1<'a> = impl for<'b> Trait<'b, Ty = Opq0<'a, 'b>>;
+    type Opq2 = impl for<'a> Trait<'a, Ty = Opq1<'a>>;
+    fn test() -> Opq2 {}
+    //~^ ERROR: expected generic lifetime parameter, found `'a`
+}
+
+fn main() {}