Rollup merge of #94235 - Dirbaio:fix-chalk-opaque-debrujin, r=jackh726

chalk: Fix wrong debrujin index in opaque type handling.

A folder in opaque type lowering was substituting all opaque type references with a variable with debrujin index 0 ignoring how many binders deep we are.

This caused an ICE with `Not enough bound vars: ^0 not found in []` ([full logs](https://gist.github.com/Dirbaio/2b9374ff4fce37afb9d665dc9f0000df)) with the following code.

```rust
fn main() -> () {}
async fn foo(x: u32) -> u32 {
    x
}
```

With the fix, it no longer ICEs. It still doesn't typecheck due to generator issues. I've added a "known-bug" test so that at least it doesn't regress back to ICEing.

r? ``@jackh726``

compiler/rustc_traits/src/chalk/db.rs

@@ -8,7 +8,7 @@
 
 use rustc_middle::traits::ChalkRustInterner as RustInterner;
 use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
-use rustc_middle::ty::{self, AssocItemContainer, AssocKind, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, AssocItemContainer, AssocKind, Ty, TyCtxt, TypeFoldable};
 
 use rustc_ast::ast;
 use rustc_attr as attr;
@@ -482,21 +482,11 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
                 .iter()
                 .map(|(bound, _)| bound.subst(self.interner.tcx, &bound_vars))
                 .map(|bound| {
-                    bound.fold_with(&mut ty::fold::BottomUpFolder {
+                    bound.fold_with(&mut ReplaceOpaqueTyFolder {
                         tcx: self.interner.tcx,
-                        ty_op: |ty| {
-                            if let ty::Opaque(def_id, substs) = *ty.kind() {
-                                if def_id == opaque_ty_id.0 && substs == identity_substs {
-                                    return self.interner.tcx.mk_ty(ty::Bound(
-                                        ty::INNERMOST,
-                                        ty::BoundTy::from(ty::BoundVar::from_u32(0)),
-                                    ));
-                                }
-                            }
-                            ty
-                        },
-                        lt_op: |lt| lt,
-                        ct_op: |ct| ct,
+                        opaque_ty_id,
+                        identity_substs,
+                        binder_index: ty::INNERMOST,
                     })
                 })
                 .filter_map(|bound| {
@@ -739,3 +729,38 @@ fn binders_for<'tcx>(
         }),
     )
 }
+
+struct ReplaceOpaqueTyFolder<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    opaque_ty_id: chalk_ir::OpaqueTyId<RustInterner<'tcx>>,
+    identity_substs: SubstsRef<'tcx>,
+    binder_index: ty::DebruijnIndex,
+}
+
+impl<'tcx> ty::TypeFolder<'tcx> for ReplaceOpaqueTyFolder<'tcx> {
+    fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn fold_binder<T: TypeFoldable<'tcx>>(
+        &mut self,
+        t: ty::Binder<'tcx, T>,
+    ) -> ty::Binder<'tcx, T> {
+        self.binder_index.shift_in(1);
+        let t = t.super_fold_with(self);
+        self.binder_index.shift_out(1);
+        t
+    }
+
+    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        if let ty::Opaque(def_id, substs) = *ty.kind() {
+            if def_id == self.opaque_ty_id.0 && substs == self.identity_substs {
+                return self.tcx.mk_ty(ty::Bound(
+                    self.binder_index,
+                    ty::BoundTy::from(ty::BoundVar::from_u32(0)),
+                ));
+            }
+        }
+        ty
+    }
+}

compiler/rustc_traits/src/chalk/lowering.rs

@@ -323,7 +323,10 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::Ty<RustInterner<'tcx>>> for Ty<'tcx> {
             ty::Closure(def_id, substs) => {
                 chalk_ir::TyKind::Closure(chalk_ir::ClosureId(def_id), substs.lower_into(interner))
             }
-            ty::Generator(_def_id, _substs, _) => unimplemented!(),
+            ty::Generator(def_id, substs, _) => chalk_ir::TyKind::Generator(
+                chalk_ir::GeneratorId(def_id),
+                substs.lower_into(interner),
+            ),
             ty::GeneratorWitness(_) => unimplemented!(),
             ty::Never => chalk_ir::TyKind::Never,
             ty::Tuple(types) => {

src/test/ui/chalkify/bugs/async.rs

@@ -0,0 +1,9 @@
+// check-fail
+// known-bug
+// compile-flags: -Z chalk --edition=2021
+
+fn main() -> () {}
+
+async fn foo(x: u32) -> u32 {
+    x
+}

src/test/ui/chalkify/bugs/async.stderr

@@ -0,0 +1,39 @@
+error[E0277]: the trait bound `[static generator@$DIR/async.rs:7:29: 9:2]: Generator<ResumeTy>` is not satisfied
+  --> $DIR/async.rs:7:29
+   |
+LL |   async fn foo(x: u32) -> u32 {
+   |  _____________________________^
+LL | |     x
+LL | | }
+   | |_^ the trait `Generator<ResumeTy>` is not implemented for `[static generator@$DIR/async.rs:7:29: 9:2]`
+   |
+note: required by a bound in `from_generator`
+  --> $SRC_DIR/core/src/future/mod.rs:LL:COL
+   |
+LL |     T: Generator<ResumeTy, Yield = ()>,
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `from_generator`
+
+error[E0280]: the requirement `<[static generator@$DIR/async.rs:7:29: 9:2] as Generator<ResumeTy>>::Yield == ()` is not satisfied
+  --> $DIR/async.rs:7:29
+   |
+LL |   async fn foo(x: u32) -> u32 {
+   |  _____________________________^
+LL | |     x
+LL | | }
+   | |_^
+   |
+note: required by a bound in `from_generator`
+  --> $SRC_DIR/core/src/future/mod.rs:LL:COL
+   |
+LL |     T: Generator<ResumeTy, Yield = ()>,
+   |                            ^^^^^^^^^^ required by this bound in `from_generator`
+
+error[E0280]: the requirement `<impl Future<Output = [async output]> as Future>::Output == u32` is not satisfied
+  --> $DIR/async.rs:7:25
+   |
+LL | async fn foo(x: u32) -> u32 {
+   |                         ^^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

src/tools/tidy/src/error_codes_check.rs

@@ -10,8 +10,8 @@ use regex::Regex;
 
 // A few of those error codes can't be tested but all the others can and *should* be tested!
 const EXEMPTED_FROM_TEST: &[&str] = &[
-    "E0279", "E0280", "E0313", "E0377", "E0461", "E0462", "E0465", "E0476", "E0514", "E0519",
-    "E0523", "E0554", "E0640", "E0717", "E0729",
+    "E0279", "E0313", "E0377", "E0461", "E0462", "E0465", "E0476", "E0514", "E0519", "E0523",
+    "E0554", "E0640", "E0717", "E0729",
 ];
 
 // Some error codes don't have any tests apparently...