Fix missing type alias cycle detection

GuillaumeGomez · GuillaumeGomez · commit c383c9daded5 · 2022-10-29T15:09:05.000+02:00
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -14,8 +14,8 @@ use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
 use rustc_middle::ty::{
-    self, AdtKind, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable,
-    TypeSuperVisitable, TypeVisitable, TypeVisitor,
+    self, AdtKind, DefIdTree, GenericParamDefKind, SubstsRef, ToPredicate, Ty, TyCtxt,
+    TypeFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
 use rustc_middle::ty::{GenericArgKind, InternalSubsts};
 use rustc_session::parse::feature_err;
@@ -239,6 +239,51 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
         hir::ItemKind::TraitAlias(..) => {
             check_trait(tcx, item);
         }
+        hir::ItemKind::TyAlias { .. } => {
+            struct TyAliasPeeler<'t> {
+                tcx: TyCtxt<'t>,
+                visited: FxHashSet<(DefId, SubstsRef<'t>)>,
+            }
+
+            impl<'t> ty::TypeFolder<'t> for TyAliasPeeler<'t> {
+                fn tcx<'a>(&'a self) -> TyCtxt<'t> {
+                    self.tcx
+                }
+
+                fn fold_ty(&mut self, t: Ty<'t>) -> Ty<'t> {
+                    use crate::ty::fold::{TypeFoldable, TypeSuperFoldable};
+                    use crate::ty::visit::TypeVisitable;
+
+                    match *t.kind() {
+                        ty::TyAlias(def_id, substs) => {
+                            if !self.visited.insert((def_id, substs)) {
+                                let def_span = self.tcx.def_span(def_id);
+                                self.tcx
+                                    .sess
+                                    .struct_span_err(
+                                        def_span,
+                                        "cycle detected when expanding type alias",
+                                    )
+                                    .emit();
+                                return t;
+                            }
+                            let binder_ty = self.tcx.bound_type_of(def_id);
+                            let ty = binder_ty.subst(self.tcx, substs);
+                            ty.fold_with(self)
+                        }
+                        _ if !t.has_ty_alias() => t,
+                        _ => t.super_fold_with(self),
+                    }
+                }
+            }
+
+            let ty = tcx.bound_type_of(item.def_id.to_def_id()).0;
+            if let ty::TyAlias(def_id, substs) = *ty.kind() {
+                let binder_ty = tcx.bound_type_of(def_id);
+                let ty = binder_ty.subst(tcx, substs);
+                ty.fold_with(&mut TyAliasPeeler { tcx, visited: FxHashSet::default() });
+            }
+        }
         // `ForeignItem`s are handled separately.
         hir::ItemKind::ForeignMod { .. } => {}
         _ => {}
diff --git a/compiler/rustc_hir_analysis/src/variance/constraints.rs b/compiler/rustc_hir_analysis/src/variance/constraints.rs
@@ -7,7 +7,7 @@ use hir::def_id::{DefId, LocalDefId};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
-use rustc_middle::ty::{self, Subst, Ty, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt};
 
 use super::terms::VarianceTerm::*;
 use super::terms::*;
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
@@ -9,7 +9,7 @@ use rustc_macros::LintDiagnostic;
 use rustc_middle::ty::layout::{IntegerExt, LayoutOf, SizeSkeleton};
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{
-    self, AdtKind, DefIdTree, Subst, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
+    self, AdtKind, DefIdTree, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
 };
 use rustc_span::source_map;
 use rustc_span::symbol::sym;
diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
@@ -28,7 +28,7 @@ use rustc_middle::span_bug;
 use rustc_middle::ty::abstract_const::{walk_abstract_const, AbstractConst, Node as ACNode};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::subst::InternalSubsts;
-use rustc_middle::ty::{self, Const, DefIdTree, GenericParamDefKind, Subst};
+use rustc_middle::ty::{self, Const, DefIdTree, GenericParamDefKind};
 use rustc_middle::ty::{TraitRef, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor};
 use rustc_session::lint;
 use rustc_span::hygiene::Transparency;
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -30,7 +30,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_infer::infer::resolve::OpportunisticRegionResolver;
 use rustc_middle::traits::select::OverflowError;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
-use rustc_middle::ty::subst::{Subst, SubstsRef};
+use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable};
 use rustc_middle::ty::DefIdTree;
 use rustc_middle::ty::{self, Term, ToPredicate, Ty, TyCtxt};
diff --git a/compiler/rustc_trait_selection/src/traits/query/normalize.rs b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
@@ -13,7 +13,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir::def_id::DefId;
 use rustc_infer::traits::Normalized;
 use rustc_middle::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeSuperFoldable};
-use rustc_middle::ty::subst::{Subst, SubstsRef};
+use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitable};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitor};
 use rustc_span::DUMMY_SP;
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -5,7 +5,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
 use rustc_middle::ty::walk::TypeWalker;
-use rustc_middle::ty::{self, ParamEnv, Subst, ToPredicate, Ty, TyCtxt, TypeVisitable};
+use rustc_middle::ty::{self, ParamEnv, ToPredicate, Ty, TyCtxt, TypeVisitable};
 use rustc_span::Span;
 
 use std::iter;
@@ -506,9 +506,9 @@ impl<'tcx> WfPredicates<'tcx> {
                         cause,
                         depth,
                         param_env,
-                        ty::Binder::dummy(ty::PredicateKind::TypeOutlives(
-                            ty::OutlivesPredicate(rty, r),
-                        ))
+                        ty::Binder::dummy(ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(
+                            rty, r,
+                        )))
                         .to_predicate(self.tcx()),
                     ));
                 }
@@ -606,8 +606,7 @@ impl<'tcx> WfPredicates<'tcx> {
                             cause.clone(),
                             depth,
                             param_env,
-                            ty::Binder::dummy(ty::PredicateKind::ObjectSafe(did))
-                                .to_predicate(tcx),
+                            ty::Binder::dummy(ty::PredicateKind::ObjectSafe(did)).to_predicate(tcx),
                         )
                     }));
                 }
diff --git a/src/test/ui/infinite/infinite-type-alias-mutual-recursion.rs b/src/test/ui/infinite/infinite-type-alias-mutual-recursion.rs
@@ -1,6 +1,8 @@
 type X1 = X2;
-//~^ ERROR cycle detected when expanding type alias `X1`
+//~^ ERROR cycle detected when expanding type alias
 type X2 = X3;
+//~^ ERROR cycle detected when expanding type alias
 type X3 = X1;
+//~^ ERROR cycle detected when expanding type alias
 
 fn main() {}
diff --git a/src/test/ui/infinite/infinite-type-alias-mutual-recursion.stderr b/src/test/ui/infinite/infinite-type-alias-mutual-recursion.stderr
@@ -1,34 +1,20 @@
-error[E0391]: cycle detected when expanding type alias `X1`
-  --> $DIR/infinite-type-alias-mutual-recursion.rs:1:11
-   |
-LL | type X1 = X2;
-   |           ^^
-   |
-note: ...which requires expanding type alias `X2`...
-  --> $DIR/infinite-type-alias-mutual-recursion.rs:3:11
-   |
-LL | type X2 = X3;
-   |           ^^
-note: ...which requires expanding type alias `X3`...
-  --> $DIR/infinite-type-alias-mutual-recursion.rs:4:11
+error: cycle detected when expanding type alias
+  --> $DIR/infinite-type-alias-mutual-recursion.rs:5:1
    |
 LL | type X3 = X1;
-   |           ^^
-   = note: ...which again requires expanding type alias `X1`, completing the cycle
-   = note: type aliases cannot be recursive
-   = help: consider using a struct, enum, or union instead to break the cycle
-   = help: see <https://doc.rust-lang.org/reference/types.html#recursive-types> for more information
-note: cycle used when collecting item types in top-level module
+   | ^^^^^^^
+
+error: cycle detected when expanding type alias
   --> $DIR/infinite-type-alias-mutual-recursion.rs:1:1
    |
-LL | / type X1 = X2;
-LL | |
-LL | | type X2 = X3;
-LL | | type X3 = X1;
-LL | |
-LL | | fn main() {}
-   | |____________^
+LL | type X1 = X2;
+   | ^^^^^^^
+
+error: cycle detected when expanding type alias
+  --> $DIR/infinite-type-alias-mutual-recursion.rs:3:1
+   |
+LL | type X2 = X3;
+   | ^^^^^^^
 
-error: aborting due to previous error
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0391`.
