Rollup merge of #120139 - compiler-errors:fnonce-shim, r=BoxyUwU

Do not normalize closure signature when building `FnOnce` shim

It is not necessary to normalize the closure signature when building an `FnOnce` shim for an `Fn`/`FnMut` closure. That closure shim is just calling `FnMut::call_mut(&mut self)` anyways.

It's also somewhat sketchy that we were ever doing this to begin with, since we're normalizing with a `ParamEnv::reveal_all()` param-env, which is definitely not right with possibly polymorphic substs.

This cuts out a tiny bit of unnecessary work in `Instance::resolve` and simplifies the signature because now we can unconditionally return an `Instance`.

Author: fmease

Diff for: compiler/rustc_codegen_cranelift/src/base.rs

@@ -682,7 +682,6 @@ fn codegen_stmt<'tcx>(
                                 args,
                                 ty::ClosureKind::FnOnce,
                             )
-                            .expect("failed to normalize and resolve closure during codegen")
                             .polymorphize(fx.tcx);
                             let func_ref = fx.get_function_ref(instance);
                             let func_addr = fx.bcx.ins().func_addr(fx.pointer_type, func_ref);

Diff for: compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -435,7 +435,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                                     args,
                                     ty::ClosureKind::FnOnce,
                                 )
-                                .expect("failed to normalize and resolve closure during codegen")
                                 .polymorphize(bx.cx().tcx());
                                 OperandValue::Immediate(bx.cx().get_fn_addr(instance))
                             }

Diff for: compiler/rustc_const_eval/src/interpret/cast.rs

@@ -117,8 +117,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                             def_id,
                             args,
                             ty::ClosureKind::FnOnce,
-                        )
-                        .ok_or_else(|| err_inval!(TooGeneric))?;
+                        );
                         let fn_ptr = self.fn_ptr(FnVal::Instance(instance));
                         self.write_pointer(fn_ptr, dest)?;
                     }

Diff for: compiler/rustc_middle/src/ty/instance.rs

@@ -530,12 +530,12 @@ impl<'tcx> Instance<'tcx> {
         def_id: DefId,
         args: ty::GenericArgsRef<'tcx>,
         requested_kind: ty::ClosureKind,
-    ) -> Option<Instance<'tcx>> {
+    ) -> Instance<'tcx> {
         let actual_kind = args.as_closure().kind();
 
         match needs_fn_once_adapter_shim(actual_kind, requested_kind) {
             Ok(true) => Instance::fn_once_adapter_instance(tcx, def_id, args),
-            _ => Some(Instance::new(def_id, args)),
+            _ => Instance::new(def_id, args),
         }
     }
 
@@ -550,7 +550,7 @@ impl<'tcx> Instance<'tcx> {
         tcx: TyCtxt<'tcx>,
         closure_did: DefId,
         args: ty::GenericArgsRef<'tcx>,
-    ) -> Option<Instance<'tcx>> {
+    ) -> Instance<'tcx> {
         let fn_once = tcx.require_lang_item(LangItem::FnOnce, None);
         let call_once = tcx
             .associated_items(fn_once)
@@ -564,14 +564,12 @@ impl<'tcx> Instance<'tcx> {
 
         let self_ty = Ty::new_closure(tcx, closure_did, args);
 
-        let sig = args.as_closure().sig();
-        let sig =
-            tcx.try_normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), sig).ok()?;
-        assert_eq!(sig.inputs().len(), 1);
-        let args = tcx.mk_args_trait(self_ty, [sig.inputs()[0].into()]);
+        let tupled_inputs_ty = args.as_closure().sig().map_bound(|sig| sig.inputs()[0]);
+        let tupled_inputs_ty = tcx.instantiate_bound_regions_with_erased(tupled_inputs_ty);
+        let args = tcx.mk_args_trait(self_ty, [tupled_inputs_ty.into()]);
 
-        debug!(?self_ty, ?sig);
-        Some(Instance { def, args })
+        debug!(?self_ty, args=?tupled_inputs_ty.tuple_fields());
+        Instance { def, args }
     }
 
     pub fn try_resolve_item_for_coroutine(

Diff for: compiler/rustc_monomorphize/src/collector.rs

@@ -783,8 +783,7 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
                             def_id,
                             args,
                             ty::ClosureKind::FnOnce,
-                        )
-                        .expect("failed to normalize and resolve closure during codegen");
+                        );
                         if should_codegen_locally(self.tcx, &instance) {
                             self.output.push(create_fn_mono_item(self.tcx, instance, span));
                         }

Diff for: compiler/rustc_smir/src/rustc_smir/context.rs

@@ -464,7 +464,10 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
         let def_id = def.0.internal(&mut *tables, tcx);
         let args_ref = args.internal(&mut *tables, tcx);
         let closure_kind = kind.internal(&mut *tables, tcx);
-        Instance::resolve_closure(tables.tcx, def_id, args_ref, closure_kind).stable(&mut *tables)
+        Some(
+            Instance::resolve_closure(tables.tcx, def_id, args_ref, closure_kind)
+                .stable(&mut *tables),
+        )
     }
 
     fn eval_instance(&self, def: InstanceDef, const_ty: Ty) -> Result<Allocation, Error> {

Diff for: compiler/rustc_ty_utils/src/instance.rs

@@ -265,7 +265,12 @@ fn resolve_associated_item<'tcx>(
                 match *rcvr_args.type_at(0).kind() {
                     ty::Closure(closure_def_id, args) => {
                         let trait_closure_kind = tcx.fn_trait_kind_from_def_id(trait_id).unwrap();
-                        Instance::resolve_closure(tcx, closure_def_id, args, trait_closure_kind)
+                        Some(Instance::resolve_closure(
+                            tcx,
+                            closure_def_id,
+                            args,
+                            trait_closure_kind,
+                        ))
                     }
                     ty::FnDef(..) | ty::FnPtr(..) => Some(Instance {
                         def: ty::InstanceDef::FnPtrShim(trait_item_id, rcvr_args.type_at(0)),