From 4a4fc3bb5b1efe6857cf5d6c0b554ff36b966996 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 30 Mar 2023 03:51:27 +0000
Subject: [PATCH] Implement support for GeneratorWitnessMIR in new solver

---
 .../solve/trait_goals/structural_traits.rs    | 49 +++++++++++++++++--
 .../auto-with-drop_tracking_mir.fail.stderr   | 18 +++++++
 .../new-solver/auto-with-drop_tracking_mir.rs | 26 ++++++++++
 3 files changed, 90 insertions(+), 3 deletions(-)
 create mode 100644 tests/ui/traits/new-solver/auto-with-drop_tracking_mir.fail.stderr
 create mode 100644 tests/ui/traits/new-solver/auto-with-drop_tracking_mir.rs

diff --git a/compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs b/compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs
index 9817186b874cc..a691b008e9d78 100644
--- a/compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs
+++ b/compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs
@@ -1,7 +1,9 @@
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::{def_id::DefId, Movability, Mutability};
 use rustc_infer::traits::query::NoSolution;
-use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable};
+use rustc_middle::ty::{
+    self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
+};
 
 use crate::solve::EvalCtxt;
 
@@ -60,7 +62,16 @@ pub(super) fn instantiate_constituent_tys_for_auto_trait<'tcx>(
 
         ty::GeneratorWitness(types) => Ok(ecx.instantiate_binder_with_placeholders(types).to_vec()),
 
-        ty::GeneratorWitnessMIR(..) => todo!(),
+        ty::GeneratorWitnessMIR(def_id, substs) => Ok(ecx
+            .tcx()
+            .generator_hidden_types(def_id)
+            .map(|bty| {
+                ecx.instantiate_binder_with_placeholders(replace_erased_lifetimes_with_bound_vars(
+                    tcx,
+                    bty.subst(tcx, substs),
+                ))
+            })
+            .collect()),
 
         // For `PhantomData<T>`, we pass `T`.
         ty::Adt(def, substs) if def.is_phantom_data() => Ok(vec![substs.type_at(0)]),
@@ -76,6 +87,29 @@ pub(super) fn instantiate_constituent_tys_for_auto_trait<'tcx>(
     }
 }
 
+fn replace_erased_lifetimes_with_bound_vars<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    ty: Ty<'tcx>,
+) -> ty::Binder<'tcx, Ty<'tcx>> {
+    debug_assert!(!ty.has_late_bound_regions());
+    let mut counter = 0;
+    let ty = tcx.fold_regions(ty, |mut r, current_depth| {
+        if let ty::ReErased = r.kind() {
+            let br = ty::BoundRegion {
+                var: ty::BoundVar::from_u32(counter),
+                kind: ty::BrAnon(counter, None),
+            };
+            counter += 1;
+            r = tcx.mk_re_late_bound(current_depth, br);
+        }
+        r
+    });
+    let bound_vars = tcx.mk_bound_variable_kinds_from_iter(
+        (0..counter).map(|i| ty::BoundVariableKind::Region(ty::BrAnon(i, None))),
+    );
+    ty::Binder::bind_with_vars(ty, bound_vars)
+}
+
 pub(super) fn instantiate_constituent_tys_for_sized_trait<'tcx>(
     ecx: &EvalCtxt<'_, 'tcx>,
     ty: Ty<'tcx>,
@@ -178,7 +212,16 @@ pub(super) fn instantiate_constituent_tys_for_copy_clone_trait<'tcx>(
 
         ty::GeneratorWitness(types) => Ok(ecx.instantiate_binder_with_placeholders(types).to_vec()),
 
-        ty::GeneratorWitnessMIR(..) => todo!(),
+        ty::GeneratorWitnessMIR(def_id, substs) => Ok(ecx
+            .tcx()
+            .generator_hidden_types(def_id)
+            .map(|bty| {
+                ecx.instantiate_binder_with_placeholders(replace_erased_lifetimes_with_bound_vars(
+                    ecx.tcx(),
+                    bty.subst(ecx.tcx(), substs),
+                ))
+            })
+            .collect()),
     }
 }
 
diff --git a/tests/ui/traits/new-solver/auto-with-drop_tracking_mir.fail.stderr b/tests/ui/traits/new-solver/auto-with-drop_tracking_mir.fail.stderr
new file mode 100644
index 0000000000000..6a926534e079b
--- /dev/null
+++ b/tests/ui/traits/new-solver/auto-with-drop_tracking_mir.fail.stderr
@@ -0,0 +1,18 @@
+error[E0277]: `impl Future<Output = ()>` cannot be sent between threads safely
+  --> $DIR/auto-with-drop_tracking_mir.rs:24:13
+   |
+LL |     is_send(foo());
+   |     ------- ^^^^^ `impl Future<Output = ()>` cannot be sent between threads safely
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the trait `Send` is not implemented for `impl Future<Output = ()>`
+note: required by a bound in `is_send`
+  --> $DIR/auto-with-drop_tracking_mir.rs:23:24
+   |
+LL |     fn is_send(_: impl Send) {}
+   |                        ^^^^ required by this bound in `is_send`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/traits/new-solver/auto-with-drop_tracking_mir.rs b/tests/ui/traits/new-solver/auto-with-drop_tracking_mir.rs
new file mode 100644
index 0000000000000..a5db7c4636b31
--- /dev/null
+++ b/tests/ui/traits/new-solver/auto-with-drop_tracking_mir.rs
@@ -0,0 +1,26 @@
+// compile-flags: -Ztrait-solver=next -Zdrop-tracking-mir
+// edition: 2021
+// revisions: pass fail
+//[pass] check-pass
+
+#![feature(negative_impls)]
+
+struct NotSync;
+impl !Sync for NotSync {}
+
+async fn foo() {
+    #[cfg(pass)]
+    let x = &();
+    #[cfg(fail)]
+    let x = &NotSync;
+    bar().await;
+    drop(x);
+}
+
+async fn bar() {}
+
+fn main() {
+    fn is_send(_: impl Send) {}
+    is_send(foo());
+    //[fail]~^ ERROR `impl Future<Output = ()>` cannot be sent between threads safely
+}