Rollup merge of #147152 - lcnr:instantiate-pre-sized-check, r=BoxyUwU

builtin `Fn`-trait impls: instantiate binder before the return type `Sized` check

fixes
- https://github.com/rust-lang/trait-system-refactor-initiative/issues/220
- https://github.com/rust-lang/trait-system-refactor-initiative/issues/204

r? `@BoxyUwU`

7 files changed, 134 insertions, 131 deletions

diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index c40739d12e6..9b3dc1f691f 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -664,7 +664,7 @@ fn coroutine_closure_to_ambiguous_coroutine<I: Interner>(
 pub(in crate::solve) fn extract_fn_def_from_const_callable<I: Interner>(
     cx: I,
     self_ty: I::Ty,
-) -> Result<(ty::Binder<I, (I::FnInputTys, I::Ty)>, I::FunctionId, I::GenericArgs), NoSolution> {
+) -> Result<(ty::Binder<I, (I::Ty, I::Ty)>, I::FunctionId, I::GenericArgs), NoSolution> {
     match self_ty.kind() {
         ty::FnDef(def_id, args) => {
             let sig = cx.fn_sig(def_id);
@@ -673,7 +673,8 @@ pub(in crate::solve) fn extract_fn_def_from_const_callable<I: Interner>(
                 && cx.fn_is_const(def_id)
             {
                 Ok((
-                    sig.instantiate(cx, args).map_bound(|sig| (sig.inputs(), sig.output())),
+                    sig.instantiate(cx, args)
+                        .map_bound(|sig| (Ty::new_tup(cx, sig.inputs().as_slice()), sig.output())),
                     def_id,
                     args,
                 ))
diff --git a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
index cb72c1cd92b..65a5edf6b72 100644
--- a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
@@ -234,12 +234,12 @@ where
         let self_ty = goal.predicate.self_ty();
         let (inputs_and_output, def_id, args) =
             structural_traits::extract_fn_def_from_const_callable(cx, self_ty)?;
+        let (inputs, output) = ecx.instantiate_binder_with_infer(inputs_and_output);
 
         // A built-in `Fn` impl only holds if the output is sized.
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
-        let output_is_sized_pred = inputs_and_output.map_bound(|(_, output)| {
-            ty::TraitRef::new(cx, cx.require_trait_lang_item(SolverTraitLangItem::Sized), [output])
-        });
+        let output_is_sized_pred =
+            ty::TraitRef::new(cx, cx.require_trait_lang_item(SolverTraitLangItem::Sized), [output]);
         let requirements = cx
             .const_conditions(def_id.into())
             .iter_instantiated(cx, args)
@@ -251,15 +251,12 @@ where
             })
             .chain([(GoalSource::ImplWhereBound, goal.with(cx, output_is_sized_pred))]);
 
-        let pred = inputs_and_output
-            .map_bound(|(inputs, _)| {
-                ty::TraitRef::new(
-                    cx,
-                    goal.predicate.def_id(),
-                    [goal.predicate.self_ty(), Ty::new_tup(cx, inputs.as_slice())],
-                )
-            })
-            .to_host_effect_clause(cx, goal.predicate.constness);
+        let pred = ty::Binder::dummy(ty::TraitRef::new(
+            cx,
+            goal.predicate.def_id(),
+            [goal.predicate.self_ty(), inputs],
+        ))
+        .to_host_effect_clause(cx, goal.predicate.constness);
 
         Self::probe_and_consider_implied_clause(
             ecx,
diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
index 85110530ae9..f25003bbfe9 100644
--- a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
@@ -633,28 +633,19 @@ where
     // the certainty of all the goals.
     #[instrument(level = "trace", skip(self))]
     pub(super) fn try_evaluate_added_goals(&mut self) -> Result<Certainty, NoSolution> {
-        let mut response = Ok(Certainty::overflow(false));
         for _ in 0..FIXPOINT_STEP_LIMIT {
-            // FIXME: This match is a bit ugly, it might be nice to change the inspect
-            // stuff to use a closure instead. which should hopefully simplify this a bit.
             match self.evaluate_added_goals_step() {
-                Ok(Some(cert)) => {
-                    response = Ok(cert);
-                    break;
-                }
                 Ok(None) => {}
+                Ok(Some(cert)) => return Ok(cert),
                 Err(NoSolution) => {
-                    response = Err(NoSolution);
-                    break;
+                    self.tainted = Err(NoSolution);
+                    return Err(NoSolution);
                 }
             }
         }
 
-        if response.is_err() {
-            self.tainted = Err(NoSolution);
-        }
-
-        response
+        debug!("try_evaluate_added_goals: encountered overflow");
+        Ok(Certainty::overflow(false))
     }
 
     /// Iterate over all added goals: returning `Ok(Some(_))` in case we can stop rerunning.
diff --git a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
index 653c59c5d42..0674b3d42ab 100644
--- a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
@@ -451,23 +451,22 @@ where
                     return ecx.forced_ambiguity(MaybeCause::Ambiguity);
                 }
             };
+        let (inputs, output) = ecx.instantiate_binder_with_infer(tupled_inputs_and_output);
 
         // A built-in `Fn` impl only holds if the output is sized.
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
-        let output_is_sized_pred = tupled_inputs_and_output.map_bound(|(_, output)| {
-            ty::TraitRef::new(cx, cx.require_trait_lang_item(SolverTraitLangItem::Sized), [output])
-        });
+        let output_is_sized_pred =
+            ty::TraitRef::new(cx, cx.require_trait_lang_item(SolverTraitLangItem::Sized), [output]);
 
-        let pred = tupled_inputs_and_output
-            .map_bound(|(inputs, output)| ty::ProjectionPredicate {
-                projection_term: ty::AliasTerm::new(
-                    cx,
-                    goal.predicate.def_id(),
-                    [goal.predicate.self_ty(), inputs],
-                ),
-                term: output.into(),
-            })
-            .upcast(cx);
+        let pred = ty::ProjectionPredicate {
+            projection_term: ty::AliasTerm::new(
+                cx,
+                goal.predicate.def_id(),
+                [goal.predicate.self_ty(), inputs],
+            ),
+            term: output.into(),
+        }
+        .upcast(cx);
 
         Self::probe_and_consider_implied_clause(
             ecx,
@@ -497,76 +496,56 @@ where
                 goal_kind,
                 env_region,
             )?;
+        let AsyncCallableRelevantTypes {
+            tupled_inputs_ty,
+            output_coroutine_ty,
+            coroutine_return_ty,
+        } = ecx.instantiate_binder_with_infer(tupled_inputs_and_output_and_coroutine);
 
         // A built-in `AsyncFn` impl only holds if the output is sized.
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
-        let output_is_sized_pred = tupled_inputs_and_output_and_coroutine.map_bound(
-            |AsyncCallableRelevantTypes { output_coroutine_ty: output_ty, .. }| {
-                ty::TraitRef::new(
-                    cx,
-                    cx.require_trait_lang_item(SolverTraitLangItem::Sized),
-                    [output_ty],
-                )
-            },
+        let output_is_sized_pred = ty::TraitRef::new(
+            cx,
+            cx.require_trait_lang_item(SolverTraitLangItem::Sized),
+            [output_coroutine_ty],
         );
 
-        let pred = tupled_inputs_and_output_and_coroutine
-            .map_bound(
-                |AsyncCallableRelevantTypes {
-                     tupled_inputs_ty,
-                     output_coroutine_ty,
-                     coroutine_return_ty,
-                 }| {
-                    let (projection_term, term) = if cx
-                        .is_lang_item(goal.predicate.def_id(), SolverLangItem::CallOnceFuture)
-                    {
-                        (
-                            ty::AliasTerm::new(
-                                cx,
-                                goal.predicate.def_id(),
-                                [goal.predicate.self_ty(), tupled_inputs_ty],
-                            ),
-                            output_coroutine_ty.into(),
-                        )
-                    } else if cx
-                        .is_lang_item(goal.predicate.def_id(), SolverLangItem::CallRefFuture)
-                    {
-                        (
-                            ty::AliasTerm::new(
-                                cx,
-                                goal.predicate.def_id(),
-                                [
-                                    I::GenericArg::from(goal.predicate.self_ty()),
-                                    tupled_inputs_ty.into(),
-                                    env_region.into(),
-                                ],
-                            ),
-                            output_coroutine_ty.into(),
-                        )
-                    } else if cx
-                        .is_lang_item(goal.predicate.def_id(), SolverLangItem::AsyncFnOnceOutput)
-                    {
-                        (
-                            ty::AliasTerm::new(
-                                cx,
-                                goal.predicate.def_id(),
-                                [
-                                    I::GenericArg::from(goal.predicate.self_ty()),
-                                    tupled_inputs_ty.into(),
-                                ],
-                            ),
-                            coroutine_return_ty.into(),
-                        )
-                    } else {
-                        panic!(
-                            "no such associated type in `AsyncFn*`: {:?}",
-                            goal.predicate.def_id()
-                        )
-                    };
-                    ty::ProjectionPredicate { projection_term, term }
-                },
-            )
-            .upcast(cx);
+        let (projection_term, term) =
+            if cx.is_lang_item(goal.predicate.def_id(), SolverLangItem::CallOnceFuture) {
+                (
+                    ty::AliasTerm::new(
+                        cx,
+                        goal.predicate.def_id(),
+                        [goal.predicate.self_ty(), tupled_inputs_ty],
+                    ),
+                    output_coroutine_ty.into(),
+                )
+            } else if cx.is_lang_item(goal.predicate.def_id(), SolverLangItem::CallRefFuture) {
+                (
+                    ty::AliasTerm::new(
+                        cx,
+                        goal.predicate.def_id(),
+                        [
+                            I::GenericArg::from(goal.predicate.self_ty()),
+                            tupled_inputs_ty.into(),
+                            env_region.into(),
+                        ],
+                    ),
+                    output_coroutine_ty.into(),
+                )
+            } else if cx.is_lang_item(goal.predicate.def_id(), SolverLangItem::AsyncFnOnceOutput) {
+                (
+                    ty::AliasTerm::new(
+                        cx,
+                        goal.predicate.def_id(),
+                        [goal.predicate.self_ty(), tupled_inputs_ty],
+                    ),
+                    coroutine_return_ty.into(),
+                )
+            } else {
+                panic!("no such associated type in `AsyncFn*`: {:?}", goal.predicate.def_id())
+            };
+        let pred = ty::ProjectionPredicate { projection_term, term }.upcast(cx);
 
         Self::probe_and_consider_implied_clause(
             ecx,
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index 3974114e9b4..e790ecd595b 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -369,18 +369,16 @@ where
                     return ecx.forced_ambiguity(MaybeCause::Ambiguity);
                 }
             };
+        let (inputs, output) = ecx.instantiate_binder_with_infer(tupled_inputs_and_output);
 
         // A built-in `Fn` impl only holds if the output is sized.
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
-        let output_is_sized_pred = tupled_inputs_and_output.map_bound(|(_, output)| {
-            ty::TraitRef::new(cx, cx.require_trait_lang_item(SolverTraitLangItem::Sized), [output])
-        });
+        let output_is_sized_pred =
+            ty::TraitRef::new(cx, cx.require_trait_lang_item(SolverTraitLangItem::Sized), [output]);
 
-        let pred = tupled_inputs_and_output
-            .map_bound(|(inputs, _)| {
-                ty::TraitRef::new(cx, goal.predicate.def_id(), [goal.predicate.self_ty(), inputs])
-            })
-            .upcast(cx);
+        let pred =
+            ty::TraitRef::new(cx, goal.predicate.def_id(), [goal.predicate.self_ty(), inputs])
+                .upcast(cx);
         Self::probe_and_consider_implied_clause(
             ecx,
             CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
@@ -408,28 +406,26 @@ where
                 // This region doesn't matter because we're throwing away the coroutine type
                 Region::new_static(cx),
             )?;
+        let AsyncCallableRelevantTypes {
+            tupled_inputs_ty,
+            output_coroutine_ty,
+            coroutine_return_ty: _,
+        } = ecx.instantiate_binder_with_infer(tupled_inputs_and_output_and_coroutine);
 
         // A built-in `AsyncFn` impl only holds if the output is sized.
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
-        let output_is_sized_pred = tupled_inputs_and_output_and_coroutine.map_bound(
-            |AsyncCallableRelevantTypes { output_coroutine_ty, .. }| {
-                ty::TraitRef::new(
-                    cx,
-                    cx.require_trait_lang_item(SolverTraitLangItem::Sized),
-                    [output_coroutine_ty],
-                )
-            },
+        let output_is_sized_pred = ty::TraitRef::new(
+            cx,
+            cx.require_trait_lang_item(SolverTraitLangItem::Sized),
+            [output_coroutine_ty],
         );
 
-        let pred = tupled_inputs_and_output_and_coroutine
-            .map_bound(|AsyncCallableRelevantTypes { tupled_inputs_ty, .. }| {
-                ty::TraitRef::new(
-                    cx,
-                    goal.predicate.def_id(),
-                    [goal.predicate.self_ty(), tupled_inputs_ty],
-                )
-            })
-            .upcast(cx);
+        let pred = ty::TraitRef::new(
+            cx,
+            goal.predicate.def_id(),
+            [goal.predicate.self_ty(), tupled_inputs_ty],
+        )
+        .upcast(cx);
         Self::probe_and_consider_implied_clause(
             ecx,
             CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
diff --git a/tests/ui/traits/next-solver/opaques/overflow-hr-fn-trait-sized-1.rs b/tests/ui/traits/next-solver/opaques/overflow-hr-fn-trait-sized-1.rs
new file mode 100644
index 00000000000..e35e48dfcec
--- /dev/null
+++ b/tests/ui/traits/next-solver/opaques/overflow-hr-fn-trait-sized-1.rs
@@ -0,0 +1,25 @@
+//@ ignore-compare-mode-next-solver
+//@ compile-flags: -Znext-solver
+//@ check-pass
+
+// Regression test for trait-system-refactor-initiative#220. Builtin `Fn`-trait
+// candidates required `for<'latebound> Output<'latebound>: Sized` which ended
+// up resulting in overflow if the return type is an opaque in the defining scope.
+//
+// We now eagerly instantiate the binder of the function definition which avoids
+// that overflow by relating the lifetime of the opaque to something from the
+// input.
+fn flat_map<T, F, I, G>(_: F, _: G)
+where
+    F: FnOnce(T) -> I,
+    I: Iterator,
+    G: Fn(<I as Iterator>::Item) -> usize,
+{
+}
+
+fn rarw<'a>(_: &'a ()) -> impl Iterator<Item = &'a str> {
+    flat_map(rarw, |x| x.len());
+    std::iter::empty()
+}
+
+fn main() {}
diff --git a/tests/ui/traits/next-solver/opaques/overflow-hr-fn-trait-sized-2.rs b/tests/ui/traits/next-solver/opaques/overflow-hr-fn-trait-sized-2.rs
new file mode 100644
index 00000000000..1d64e422d89
--- /dev/null
+++ b/tests/ui/traits/next-solver/opaques/overflow-hr-fn-trait-sized-2.rs
@@ -0,0 +1,14 @@
+//@ ignore-compare-mode-next-solver
+//@ compile-flags: -Znext-solver
+//@ check-pass
+
+// Regression test for trait-system-refactor-initiative#204, see
+// the sibling test for more details.
+
+fn constrain<'a, F: FnOnce(&'a ())>(_: F) {}
+fn foo<'a>(_: &'a ()) -> impl Sized + use<'a> {
+    constrain(foo);
+    ()
+}
+
+fn main() {}