From 5166f68754c58a898397e77650ae8817a2cfb9f2 Mon Sep 17 00:00:00 2001
From: Deadbeef <ent3rm4n@gmail.com>
Date: Mon, 6 Dec 2021 20:46:05 +0800
Subject: [PATCH] Fix #91489

---
 compiler/rustc_middle/src/ty/mod.rs            |  5 +++++
 compiler/rustc_typeck/src/check/closure.rs     |  2 +-
 .../non-const-op-in-closure-in-const.rs        | 18 ++++++++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/rfc-2632-const-trait-impl/non-const-op-in-closure-in-const.rs

diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index fd1409949f0..d94df488ccd 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1319,6 +1319,11 @@ pub fn with_user_facing(mut self) -> Self {
         self
     }
 
+    pub fn without_const(mut self) -> Self {
+        self.packed.set_tag(ParamTag { constness: hir::Constness::NotConst, ..self.packed.tag() });
+        self
+    }
+
     /// Returns a new parameter environment with the same clauses, but
     /// which "reveals" the true results of projections in all cases
     /// (even for associated types that are specializable). This is
diff --git a/compiler/rustc_typeck/src/check/closure.rs b/compiler/rustc_typeck/src/check/closure.rs
index 4a41552a5fb..c87ab0d410c 100644
--- a/compiler/rustc_typeck/src/check/closure.rs
+++ b/compiler/rustc_typeck/src/check/closure.rs
@@ -80,7 +80,7 @@ fn check_closure(
 
         let generator_types = check_fn(
             self,
-            self.param_env,
+            self.param_env.without_const(),
             liberated_sig,
             decl,
             expr.hir_id,
diff --git a/src/test/ui/rfc-2632-const-trait-impl/non-const-op-in-closure-in-const.rs b/src/test/ui/rfc-2632-const-trait-impl/non-const-op-in-closure-in-const.rs
new file mode 100644
index 00000000000..79e62617ead
--- /dev/null
+++ b/src/test/ui/rfc-2632-const-trait-impl/non-const-op-in-closure-in-const.rs
@@ -0,0 +1,18 @@
+// check-pass
+
+#![feature(const_trait_impl)]
+#![feature(const_fn_trait_bound)]
+
+trait Convert<T> {
+    fn to(self) -> T;
+}
+
+impl<A, B> const Convert<B> for A where B: ~const From<A> {
+    fn to(self) -> B {
+        B::from(self)
+    }
+}
+
+const FOO: fn() -> String = || "foo".to();
+
+fn main() {}
\ No newline at end of file