From 0228c073e07bc36ab4dbb88ab7f3cbdf00832d59 Mon Sep 17 00:00:00 2001
From: Andrew Cann <shum@canndrew.org>
Date: Sun, 13 Mar 2022 14:41:44 +0800
Subject: [PATCH] add generator_clone feature gate

---
 compiler/rustc_feature/src/active.rs          |  2 +
 compiler/rustc_span/src/symbol.rs             |  1 +
 .../src/traits/select/mod.rs                  | 56 +++++++++++--------
 3 files changed, 35 insertions(+), 24 deletions(-)

diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index 98258834bd5..0168587fbce 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -396,6 +396,8 @@ declare_features! (
     (active, fn_align, "1.53.0", Some(82232), None),
     /// Allows defining generators.
     (active, generators, "1.21.0", Some(43122), None),
+    /// Allows generators to be cloned.
+    (active, generator_clone, "1.60.0", None, None),
     /// Infer generic args for both consts and types.
     (active, generic_arg_infer, "1.55.0", Some(85077), None),
     /// Allows associated types to be generic, e.g., `type Foo<T>;` (RFC 1598).
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 9c3d99deae0..5bddcd34819 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -763,6 +763,7 @@ symbols! {
         gen_future,
         gen_kill,
         generator,
+        generator_clone,
         generator_state,
         generators,
         generic_arg_infer,
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 592c6c8e055..0e7483847e3 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1938,35 +1938,43 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
 
             ty::Generator(_, substs, hir::Movability::Movable) => {
-                let resolved_upvars = self.infcx.shallow_resolve(substs.as_generator().tupled_upvars_ty());
-                let resolved_witness = self.infcx.shallow_resolve(substs.as_generator().witness());
-                if {
-                    matches!(resolved_upvars.kind(), ty::Infer(ty::TyVar(_))) ||
-                    matches!(resolved_witness.kind(), ty::Infer(ty::TyVar(_)))
-                } {
-                    // Not yet resolved.
-                    Ambiguous
+                if self.tcx().features().generator_clone {
+                    let resolved_upvars = self.infcx.shallow_resolve(substs.as_generator().tupled_upvars_ty());
+                    let resolved_witness = self.infcx.shallow_resolve(substs.as_generator().witness());
+                    if {
+                        matches!(resolved_upvars.kind(), ty::Infer(ty::TyVar(_))) ||
+                        matches!(resolved_witness.kind(), ty::Infer(ty::TyVar(_)))
+                    } {
+                        // Not yet resolved.
+                        Ambiguous
+                    } else {
+                        let mut all = substs.as_generator().upvar_tys().collect::<Vec<_>>();
+                        all.push(substs.as_generator().witness());
+                        Where(obligation.predicate.rebind(all))
+                    }
                 } else {
-                    let mut all = substs.as_generator().upvar_tys().collect::<Vec<_>>();
-                    all.push(substs.as_generator().witness());
-                    Where(obligation.predicate.rebind(all))
+                    None
                 }
             }
 
             ty::GeneratorWitness(binder) => {
-                let tys = binder.no_bound_vars().unwrap();
-                let mut iter = tys.iter();
-                loop {
-                    let ty = match iter.next() {
-                        Some(ty) => ty,
-                        Option::None => {
-                            break Where(obligation.predicate.rebind(tys.to_vec()))
-                        },
-                    };
-                    let resolved = self.infcx.shallow_resolve(ty);
-                    if matches!(resolved.kind(), ty::Infer(ty::TyVar(_))) {
-                        break Ambiguous;
-                    }
+                match binder.no_bound_vars() {
+                    Some(tys) => {
+                        let mut iter = tys.iter();
+                        loop {
+                            let ty = match iter.next() {
+                                Some(ty) => ty,
+                                Option::None => {
+                                    break Where(obligation.predicate.rebind(tys.to_vec()))
+                                },
+                            };
+                            let resolved = self.infcx.shallow_resolve(ty);
+                            if matches!(resolved.kind(), ty::Infer(ty::TyVar(_))) {
+                                break Ambiguous;
+                            }
+                        }
+                    },
+                    Option::None => None,
                 }
             }