Check that closures satisfy their where bounds

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -1,11 +1,8 @@
-use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::vec_map::VecMap;
 use rustc_hir::def_id::DefId;
 use rustc_hir::OpaqueTyOrigin;
 use rustc_infer::infer::InferCtxt;
-use rustc_middle::ty::subst::GenericArgKind;
 use rustc_middle::ty::{self, OpaqueHiddenType, OpaqueTypeKey, TyCtxt, TypeFoldable};
-use rustc_span::Span;
 use rustc_trait_selection::opaque_types::InferCtxtExt;
 
 use super::RegionInferenceContext;
@@ -107,21 +104,11 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
             let opaque_type_key =
                 OpaqueTypeKey { def_id: opaque_type_key.def_id, substs: universal_substs };
-            let remapped_type = infcx.infer_opaque_definition_from_instantiation(
+            let ty = infcx.infer_opaque_definition_from_instantiation(
                 opaque_type_key,
                 universal_concrete_type,
                 origin,
             );
-            let ty = if check_opaque_type_parameter_valid(
-                infcx.tcx,
-                opaque_type_key,
-                origin,
-                concrete_type.span,
-            ) {
-                remapped_type
-            } else {
-                infcx.tcx.ty_error()
-            };
             // Sometimes two opaque types are the same only after we remap the generic parameters
             // back to the opaque type definition. E.g. we may have `OpaqueType<X, Y>` mapped to `(X, Y)`
             // and `OpaqueType<Y, X>` mapped to `(Y, X)`, and those are the same, but we only know that
@@ -184,95 +171,3 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         })
     }
 }
-
-fn check_opaque_type_parameter_valid(
-    tcx: TyCtxt<'_>,
-    opaque_type_key: OpaqueTypeKey<'_>,
-    origin: OpaqueTyOrigin,
-    span: Span,
-) -> bool {
-    match origin {
-        // No need to check return position impl trait (RPIT)
-        // because for type and const parameters they are correct
-        // by construction: we convert
-        //
-        // fn foo<P0..Pn>() -> impl Trait
-        //
-        // into
-        //
-        // type Foo<P0...Pn>
-        // fn foo<P0..Pn>() -> Foo<P0...Pn>.
-        //
-        // For lifetime parameters we convert
-        //
-        // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
-        //
-        // into
-        //
-        // type foo::<'p0..'pn>::Foo<'q0..'qm>
-        // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
-        //
-        // which would error here on all of the `'static` args.
-        OpaqueTyOrigin::FnReturn(..) | OpaqueTyOrigin::AsyncFn(..) => return true,
-        // Check these
-        OpaqueTyOrigin::TyAlias => {}
-    }
-    let opaque_generics = tcx.generics_of(opaque_type_key.def_id);
-    let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default();
-    for (i, arg) in opaque_type_key.substs.iter().enumerate() {
-        let arg_is_param = match arg.unpack() {
-            GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
-            GenericArgKind::Lifetime(lt) if lt.is_static() => {
-                tcx.sess
-                    .struct_span_err(span, "non-defining opaque type use in defining scope")
-                    .span_label(
-                        tcx.def_span(opaque_generics.param_at(i, tcx).def_id),
-                        "cannot use static lifetime; use a bound lifetime \
-                                    instead or remove the lifetime parameter from the \
-                                    opaque type",
-                    )
-                    .emit();
-                return false;
-            }
-            GenericArgKind::Lifetime(lt) => {
-                matches!(*lt, ty::ReEarlyBound(_) | ty::ReFree(_))
-            }
-            GenericArgKind::Const(ct) => matches!(ct.val(), ty::ConstKind::Param(_)),
-        };
-
-        if arg_is_param {
-            seen_params.entry(arg).or_default().push(i);
-        } else {
-            // Prevent `fn foo() -> Foo<u32>` from being defining.
-            let opaque_param = opaque_generics.param_at(i, tcx);
-            tcx.sess
-                .struct_span_err(span, "non-defining opaque type use in defining scope")
-                .span_note(
-                    tcx.def_span(opaque_param.def_id),
-                    &format!(
-                        "used non-generic {} `{}` for generic parameter",
-                        opaque_param.kind.descr(),
-                        arg,
-                    ),
-                )
-                .emit();
-            return false;
-        }
-    }
-
-    for (_, indices) in seen_params {
-        if indices.len() > 1 {
-            let descr = opaque_generics.param_at(indices[0], tcx).kind.descr();
-            let spans: Vec<_> = indices
-                .into_iter()
-                .map(|i| tcx.def_span(opaque_generics.param_at(i, tcx).def_id))
-                .collect();
-            tcx.sess
-                .struct_span_err(span, "non-defining opaque type use in defining scope")
-                .span_note(spans, &format!("{} used multiple times", descr))
-                .emit();
-            return false;
-        }
-    }
-    true
-}

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -82,6 +82,15 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         ));
         debug!(?definition_ty);
 
+        if !check_opaque_type_parameter_valid(
+            self.tcx,
+            opaque_type_key,
+            origin,
+            instantiated_ty.span,
+        ) {
+            return self.tcx.ty_error();
+        }
+
         // Only check this for TAIT. RPIT already supports `src/test/ui/impl-trait/nested-return-type2.rs`
         // on stable and we'd break that.
         if let OpaqueTyOrigin::TyAlias = origin {
@@ -148,6 +157,98 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
     }
 }
 
+fn check_opaque_type_parameter_valid(
+    tcx: TyCtxt<'_>,
+    opaque_type_key: OpaqueTypeKey<'_>,
+    origin: OpaqueTyOrigin,
+    span: Span,
+) -> bool {
+    match origin {
+        // No need to check return position impl trait (RPIT)
+        // because for type and const parameters they are correct
+        // by construction: we convert
+        //
+        // fn foo<P0..Pn>() -> impl Trait
+        //
+        // into
+        //
+        // type Foo<P0...Pn>
+        // fn foo<P0..Pn>() -> Foo<P0...Pn>.
+        //
+        // For lifetime parameters we convert
+        //
+        // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
+        //
+        // into
+        //
+        // type foo::<'p0..'pn>::Foo<'q0..'qm>
+        // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
+        //
+        // which would error here on all of the `'static` args.
+        OpaqueTyOrigin::FnReturn(..) | OpaqueTyOrigin::AsyncFn(..) => return true,
+        // Check these
+        OpaqueTyOrigin::TyAlias => {}
+    }
+    let opaque_generics = tcx.generics_of(opaque_type_key.def_id);
+    let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default();
+    for (i, arg) in opaque_type_key.substs.iter().enumerate() {
+        let arg_is_param = match arg.unpack() {
+            GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
+            GenericArgKind::Lifetime(lt) if lt.is_static() => {
+                tcx.sess
+                    .struct_span_err(span, "non-defining opaque type use in defining scope")
+                    .span_label(
+                        tcx.def_span(opaque_generics.param_at(i, tcx).def_id),
+                        "cannot use static lifetime; use a bound lifetime \
+                                    instead or remove the lifetime parameter from the \
+                                    opaque type",
+                    )
+                    .emit();
+                return false;
+            }
+            GenericArgKind::Lifetime(lt) => {
+                matches!(*lt, ty::ReEarlyBound(_) | ty::ReFree(_))
+            }
+            GenericArgKind::Const(ct) => matches!(ct.val(), ty::ConstKind::Param(_)),
+        };
+
+        if arg_is_param {
+            seen_params.entry(arg).or_default().push(i);
+        } else {
+            // Prevent `fn foo() -> Foo<u32>` from being defining.
+            let opaque_param = opaque_generics.param_at(i, tcx);
+            tcx.sess
+                .struct_span_err(span, "non-defining opaque type use in defining scope")
+                .span_note(
+                    tcx.def_span(opaque_param.def_id),
+                    &format!(
+                        "used non-generic {} `{}` for generic parameter",
+                        opaque_param.kind.descr(),
+                        arg,
+                    ),
+                )
+                .emit();
+            return false;
+        }
+    }
+
+    for (_, indices) in seen_params {
+        if indices.len() > 1 {
+            let descr = opaque_generics.param_at(indices[0], tcx).kind.descr();
+            let spans: Vec<_> = indices
+                .into_iter()
+                .map(|i| tcx.def_span(opaque_generics.param_at(i, tcx).def_id))
+                .collect();
+            tcx.sess
+                .struct_span_err(span, "non-defining opaque type use in defining scope")
+                .span_note(spans, &format!("{} used multiple times", descr))
+                .emit();
+            return false;
+        }
+    }
+    true
+}
+
 struct ReverseMapper<'tcx> {
     tcx: TyCtxt<'tcx>,
 

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -575,7 +575,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                     // generators don't take arguments.
                 }
 
-                ty::Closure(_, substs) => {
+                ty::Closure(did, substs) => {
                     // Only check the upvar types for WF, not the rest
                     // of the types within. This is needed because we
                     // capture the signature and it may not be WF
@@ -596,18 +596,26 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                     // probably always be WF, because it should be
                     // shorthand for something like `where(T: 'a) {
                     // fn(&'a T) }`, as discussed in #25860.
-                    //
-                    // Note that we are also skipping the generic
-                    // types. This is consistent with the `outlives`
-                    // code, but anyway doesn't matter: within the fn
+                    walker.skip_current_subtree(); // subtree handled below
+                    // FIXME(eddyb) add the type to `walker` instead of recursing.
+                    self.compute(substs.as_closure().tupled_upvars_ty().into());
+                    // Note that we cannot skip the generic types
+                    // types. Normally, within the fn
                     // body where they are created, the generics will
                     // always be WF, and outside of that fn body we
                     // are not directly inspecting closure types
                     // anyway, except via auto trait matching (which
                     // only inspects the upvar types).
-                    walker.skip_current_subtree(); // subtree handled below
-                    // FIXME(eddyb) add the type to `walker` instead of recursing.
-                    self.compute(substs.as_closure().tupled_upvars_ty().into());
+                    // But when a closure is part of a type-alias-impl-trait
+                    // then the function that created the defining site may
+                    // have had more bounds available than the type alias
+                    // specifies. This may cause us to have a closure in the
+                    // hidden type that is not actually well formed and
+                    // can cause compiler crashes when the user abuses unsafe
+                    // code to procure such a closure.
+                    // See src/test/ui/type-alias-impl-trait/wf_check_closures.rs
+                    let obligations = self.nominal_obligations(did, substs);
+                    self.out.extend(obligations);
                 }
 
                 ty::FnPtr(_) => {

src/test/ui/const-generics/generic_const_exprs/closures.rs

@@ -1,6 +1,6 @@
 #![feature(generic_const_exprs)]
 #![allow(incomplete_features)]
 fn test<const N: usize>() -> [u8; N + (|| 42)()] {}
-//~^ ERROR overly complex generic constant
+//~^ ERROR cycle detected when building an abstract representation
 
 fn main() {}

src/test/ui/const-generics/generic_const_exprs/closures.stderr

@@ -1,13 +1,26 @@
-error: overly complex generic constant
+error[E0391]: cycle detected when building an abstract representation for test::{constant#0}
   --> $DIR/closures.rs:3:35
    |
 LL | fn test<const N: usize>() -> [u8; N + (|| 42)()] {}
-   |                                   ^^^^-------^^
-   |                                       |
-   |                                       borrowing is not supported in generic constants
+   |                                   ^^^^^^^^^^^^^
    |
-   = help: consider moving this anonymous constant into a `const` function
-   = note: this operation may be supported in the future
+note: ...which requires building THIR for `test::{constant#0}`...
+  --> $DIR/closures.rs:3:35
+   |
+LL | fn test<const N: usize>() -> [u8; N + (|| 42)()] {}
+   |                                   ^^^^^^^^^^^^^
+note: ...which requires type-checking `test::{constant#0}`...
+  --> $DIR/closures.rs:3:35
+   |
+LL | fn test<const N: usize>() -> [u8; N + (|| 42)()] {}
+   |                                   ^^^^^^^^^^^^^
+   = note: ...which again requires building an abstract representation for test::{constant#0}, completing the cycle
+note: cycle used when checking that `test` is well-formed
+  --> $DIR/closures.rs:3:1
+   |
+LL | fn test<const N: usize>() -> [u8; N + (|| 42)()] {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0391`.

src/test/ui/higher-rank-trait-bounds/issue-59311.nll.stderr

@@ -0,0 +1,18 @@
+error: higher-ranked lifetime error
+  --> $DIR/issue-59311.rs:17:5
+   |
+LL |     v.t(|| {});
+   |     ^^^^^^^^^^
+   |
+   = note: could not prove [closure@$DIR/issue-59311.rs:17:9: 17:14] well-formed
+
+error: higher-ranked lifetime error
+  --> $DIR/issue-59311.rs:17:9
+   |
+LL |     v.t(|| {});
+   |         ^^^^^
+   |
+   = note: could not prove for<'a> &'a V: 'static
+
+error: aborting due to 2 previous errors
+

src/test/ui/higher-rank-trait-bounds/issue-59311.rs

@@ -14,7 +14,7 @@ pub fn crash<V>(v: &V)
 where
     for<'a> &'a V: T + 'static,
 {
-    v.t(|| {}); //~ ERROR: higher-ranked lifetime error
+    v.t(|| {}); //~ ERROR: `&'a V` does not fulfill the required lifetime
 }
 
 fn main() {}

src/test/ui/higher-rank-trait-bounds/issue-59311.stderr

@@ -1,10 +1,15 @@
-error: higher-ranked lifetime error
-  --> $DIR/issue-59311.rs:17:9
+error[E0477]: the type `&'a V` does not fulfill the required lifetime
+  --> $DIR/issue-59311.rs:17:5
    |
 LL |     v.t(|| {});
-   |         ^^^^^
+   |     ^^^^^^^^^^
    |
-   = note: could not prove for<'a> &'a V: 'static
+note: type must satisfy the static lifetime as required by this binding
+  --> $DIR/issue-59311.rs:15:24
+   |
+LL |     for<'a> &'a V: T + 'static,
+   |                        ^^^^^^^
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0477`.

src/test/ui/type-alias-impl-trait/generic_duplicate_param_use.rs

@@ -15,7 +15,6 @@ type TwoConsts<const X: usize, const Y: usize> = impl Debug;
 fn one_ty<T: Debug>(t: T) -> TwoTys<T, T> {
     t
     //~^ ERROR non-defining opaque type use in defining scope
-    //~| ERROR `U` doesn't implement `Debug`
 }
 
 fn one_lifetime<'a>(t: &'a u32) -> TwoLifetimes<'a, 'a> {