From 9a1043eac7dbd7177ce032c0f777b5ee2f636621 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sun, 6 Nov 2022 01:59:03 +0000
Subject: [PATCH] Normalize signature when deducing closure signature from
 supertraits

---
 compiler/rustc_hir_typeck/src/closure.rs        | 10 +++++++---
 .../supertrait-hint-references-assoc-ty.rs      | 17 +++++++++++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)
 create mode 100644 src/test/ui/closures/supertrait-hint-references-assoc-ty.rs

diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
index 09df50c76b738..3001e79947672 100644
--- a/compiler/rustc_hir_typeck/src/closure.rs
+++ b/compiler/rustc_hir_typeck/src/closure.rs
@@ -10,6 +10,7 @@ use rustc_hir_analysis::astconv::AstConv;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::infer::LateBoundRegionConversionTime;
 use rustc_infer::infer::{InferOk, InferResult};
+use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::ty::subst::InternalSubsts;
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{self, Ty};
@@ -22,7 +23,7 @@ use std::cmp;
 use std::iter;
 
 /// What signature do we *expect* the closure to have from context?
-#[derive(Debug)]
+#[derive(Debug, Clone, TypeFoldable, TypeVisitable)]
 struct ExpectedSig<'tcx> {
     /// Span that gave us this expectation, if we know that.
     cause_span: Option<Span>,
@@ -241,9 +242,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             if expected_sig.is_none()
                 && let ty::PredicateKind::Projection(proj_predicate) = bound_predicate.skip_binder()
             {
-                expected_sig = self.deduce_sig_from_projection(
+                expected_sig = self.normalize_associated_types_in(
+                    obligation.cause.span,
+                    self.deduce_sig_from_projection(
                     Some(obligation.cause.span),
-                    bound_predicate.rebind(proj_predicate),
+                        bound_predicate.rebind(proj_predicate),
+                    ),
                 );
             }
 
diff --git a/src/test/ui/closures/supertrait-hint-references-assoc-ty.rs b/src/test/ui/closures/supertrait-hint-references-assoc-ty.rs
new file mode 100644
index 0000000000000..270bf14c35eca
--- /dev/null
+++ b/src/test/ui/closures/supertrait-hint-references-assoc-ty.rs
@@ -0,0 +1,17 @@
+// check-pass
+
+pub trait Fn0: Fn(i32) -> Self::Out {
+    type Out;
+}
+
+impl<F: Fn(i32) -> ()> Fn0 for F {
+    type Out = ();
+}
+
+pub fn closure_typer(_: impl Fn0) {}
+
+fn main() {
+    closure_typer(move |x| {
+        let _: i64 = x.into();
+    });
+}