From 8b494f427cb06896996fb02ac8c3ff745fde4d15 Mon Sep 17 00:00:00 2001 From: Maybe Waffle Date: Wed, 2 Feb 2022 15:09:44 +0300 Subject: [PATCH] Allow `impl Fn() -> impl Trait` in return position This allows writing the following function signatures: ```rust fn f0() -> impl Fn() -> impl Trait; fn f3() -> &'static dyn Fn() -> impl Trait; ``` These signatures were already allowed for common traits and associated types, there is no reason why `Fn*` traits should be special in this regard. --- compiler/rustc_ast_lowering/src/path.rs | 13 ++- .../ui/impl-trait/impl_fn_associativity.rs | 16 ++++ src/test/ui/impl-trait/nested_impl_trait.rs | 3 +- .../ui/impl-trait/nested_impl_trait.stderr | 8 +- src/test/ui/impl-trait/where-allowed.rs | 6 +- src/test/ui/impl-trait/where-allowed.stderr | 94 ++++++++----------- 6 files changed, 73 insertions(+), 67 deletions(-) create mode 100644 src/test/ui/impl-trait/impl_fn_associativity.rs diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs index 888776cccac2..4b7ef960d4b6 100644 --- a/compiler/rustc_ast_lowering/src/path.rs +++ b/compiler/rustc_ast_lowering/src/path.rs @@ -191,7 +191,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { self.lower_angle_bracketed_parameter_data(data, param_mode, itctx) } GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args { - ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data), + ParenthesizedGenericArgs::Ok => { + self.lower_parenthesized_parameter_data(data, itctx) + } ParenthesizedGenericArgs::Err => { // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait` let sub = if !data.inputs.is_empty() { @@ -344,6 +346,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { fn lower_parenthesized_parameter_data( &mut self, data: &ParenthesizedArgs, + itctx: ImplTraitContext, ) -> (GenericArgsCtor<'hir>, bool) { // Switch to `PassThrough` mode for anonymous lifetimes; this // means that we permit things like `&Ref`, where `Ref` has @@ -355,6 +358,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> { self.lower_ty_direct(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitParam)) })); let output_ty = match output { + // Only allow `impl Trait` in return position. i.e.: + // ```rust + // fn f(_: impl Fn() -> impl Debug) -> impl Fn() -> impl Debug + // // disallowed --^^^^^^^^^^ allowed --^^^^^^^^^^ + // ``` + FnRetTy::Ty(ty) if matches!(itctx, ImplTraitContext::ReturnPositionOpaqueTy { .. }) => { + self.lower_ty(&ty, itctx) + } FnRetTy::Ty(ty) => { self.lower_ty(&ty, &ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitReturn)) } diff --git a/src/test/ui/impl-trait/impl_fn_associativity.rs b/src/test/ui/impl-trait/impl_fn_associativity.rs new file mode 100644 index 000000000000..f5f1909cf58b --- /dev/null +++ b/src/test/ui/impl-trait/impl_fn_associativity.rs @@ -0,0 +1,16 @@ +// run-pass +use std::fmt::Debug; + +fn f_debug() -> impl Fn() -> impl Debug { + || () +} + +fn ff_debug() -> impl Fn() -> impl Fn() -> impl Debug { + || f_debug() +} + +fn main() { + // Check that `ff_debug` is `() -> (() -> Debug)` and not `(() -> ()) -> Debug` + let debug = ff_debug()()(); + assert_eq!(format!("{:?}", debug), "()"); +} diff --git a/src/test/ui/impl-trait/nested_impl_trait.rs b/src/test/ui/impl-trait/nested_impl_trait.rs index 85c6f8c462cb..9b0dbacaded8 100644 --- a/src/test/ui/impl-trait/nested_impl_trait.rs +++ b/src/test/ui/impl-trait/nested_impl_trait.rs @@ -25,8 +25,7 @@ fn allowed_in_assoc_type() -> impl Iterator { } fn allowed_in_ret_type() -> impl Fn() -> impl Into { -//~^ `impl Trait` only allowed in function and inherent method return types - || 5 + || 5u8 } fn main() {} diff --git a/src/test/ui/impl-trait/nested_impl_trait.stderr b/src/test/ui/impl-trait/nested_impl_trait.stderr index 3291cad6882e..e2ce7d15a069 100644 --- a/src/test/ui/impl-trait/nested_impl_trait.stderr +++ b/src/test/ui/impl-trait/nested_impl_trait.stderr @@ -40,12 +40,6 @@ error[E0562]: `impl Trait` only allowed in function and inherent method return t LL | fn bad_in_fn_syntax(x: fn() -> impl Into) {} | ^^^^^^^^^^^^^^^^^^^^^ -error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait return - --> $DIR/nested_impl_trait.rs:27:42 - | -LL | fn allowed_in_ret_type() -> impl Fn() -> impl Into { - | ^^^^^^^^^^^^^^ - error[E0277]: the trait bound `impl Debug: From>` is not satisfied --> $DIR/nested_impl_trait.rs:5:46 | @@ -64,7 +58,7 @@ LL | fn bad(x: impl Into) -> impl Into { x } = help: the trait `Into` is implemented for `T` = note: required for `impl Into` to implement `Into` -error: aborting due to 8 previous errors +error: aborting due to 7 previous errors Some errors have detailed explanations: E0277, E0562, E0666. For more information about an error, try `rustc --explain E0277`. diff --git a/src/test/ui/impl-trait/where-allowed.rs b/src/test/ui/impl-trait/where-allowed.rs index c1dd46c7ff7f..d337ab422d74 100644 --- a/src/test/ui/impl-trait/where-allowed.rs +++ b/src/test/ui/impl-trait/where-allowed.rs @@ -39,9 +39,8 @@ fn in_dyn_Fn_return_in_parameters(_: &dyn Fn() -> impl Debug) { panic!() } fn in_dyn_Fn_parameter_in_return() -> &'static dyn Fn(impl Debug) { panic!() } //~^ ERROR `impl Trait` only allowed in function and inherent method return types -// Disallowed +// Allowed fn in_dyn_Fn_return_in_return() -> &'static dyn Fn() -> impl Debug { panic!() } -//~^ ERROR `impl Trait` only allowed in function and inherent method return types // Disallowed fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() } @@ -57,9 +56,8 @@ fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() } //~^ ERROR `impl Trait` only allowed in function and inherent method return types //~| ERROR nested `impl Trait` is not allowed -// Disallowed +// Allowed fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { panic!() } -//~^ ERROR `impl Trait` only allowed in function and inherent method return types // Disallowed fn in_Fn_parameter_in_generics (_: F) { panic!() } diff --git a/src/test/ui/impl-trait/where-allowed.stderr b/src/test/ui/impl-trait/where-allowed.stderr index 2e7c7ca40ddb..1b704d0d9246 100644 --- a/src/test/ui/impl-trait/where-allowed.stderr +++ b/src/test/ui/impl-trait/where-allowed.stderr @@ -1,5 +1,5 @@ error[E0666]: nested `impl Trait` is not allowed - --> $DIR/where-allowed.rs:47:51 + --> $DIR/where-allowed.rs:46:51 | LL | fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() } | --------^^^^^^^^^^- @@ -8,7 +8,7 @@ LL | fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() } | outer `impl Trait` error[E0666]: nested `impl Trait` is not allowed - --> $DIR/where-allowed.rs:56:57 + --> $DIR/where-allowed.rs:55:57 | LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() } | --------^^^^^^^^^^- @@ -17,7 +17,7 @@ LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic | outer `impl Trait` error[E0658]: `impl Trait` in type aliases is unstable - --> $DIR/where-allowed.rs:119:16 + --> $DIR/where-allowed.rs:117:16 | LL | type Out = impl Debug; | ^^^^^^^^^^ @@ -26,7 +26,7 @@ LL | type Out = impl Debug; = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable error[E0658]: `impl Trait` in type aliases is unstable - --> $DIR/where-allowed.rs:154:23 + --> $DIR/where-allowed.rs:152:23 | LL | type InTypeAlias = impl Debug; | ^^^^^^^^^^ @@ -35,7 +35,7 @@ LL | type InTypeAlias = impl Debug; = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable error[E0658]: `impl Trait` in type aliases is unstable - --> $DIR/where-allowed.rs:157:39 + --> $DIR/where-allowed.rs:155:39 | LL | type InReturnInTypeAlias = fn() -> impl Debug; | ^^^^^^^^^^ @@ -85,80 +85,68 @@ error[E0562]: `impl Trait` only allowed in function and inherent method return t LL | fn in_dyn_Fn_parameter_in_return() -> &'static dyn Fn(impl Debug) { panic!() } | ^^^^^^^^^^ -error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait return - --> $DIR/where-allowed.rs:43:57 - | -LL | fn in_dyn_Fn_return_in_return() -> &'static dyn Fn() -> impl Debug { panic!() } - | ^^^^^^^^^^ - error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait param - --> $DIR/where-allowed.rs:47:51 + --> $DIR/where-allowed.rs:46:51 | LL | fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait return - --> $DIR/where-allowed.rs:52:53 + --> $DIR/where-allowed.rs:51:53 | LL | fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait param - --> $DIR/where-allowed.rs:56:57 + --> $DIR/where-allowed.rs:55:57 | LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() } | ^^^^^^^^^^ -error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait return - --> $DIR/where-allowed.rs:61:59 - | -LL | fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { panic!() } - | ^^^^^^^^^^ - error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait param - --> $DIR/where-allowed.rs:65:38 + --> $DIR/where-allowed.rs:63:38 | LL | fn in_Fn_parameter_in_generics (_: F) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait return - --> $DIR/where-allowed.rs:69:40 + --> $DIR/where-allowed.rs:67:40 | LL | fn in_Fn_return_in_generics impl Debug> (_: F) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:82:32 + --> $DIR/where-allowed.rs:80:32 | LL | struct InBraceStructField { x: impl Debug } | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in path - --> $DIR/where-allowed.rs:86:41 + --> $DIR/where-allowed.rs:84:41 | LL | struct InAdtInBraceStructField { x: Vec } | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:90:27 + --> $DIR/where-allowed.rs:88:27 | LL | struct InTupleStructField(impl Debug); | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:95:25 + --> $DIR/where-allowed.rs:93:25 | LL | InBraceVariant { x: impl Debug }, | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:97:20 + --> $DIR/where-allowed.rs:95:20 | LL | InTupleVariant(impl Debug), | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in trait method return - --> $DIR/where-allowed.rs:108:23 + --> $DIR/where-allowed.rs:106:23 | LL | fn in_return() -> impl Debug; | ^^^^^^^^^^ @@ -167,7 +155,7 @@ LL | fn in_return() -> impl Debug; = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `impl` method return - --> $DIR/where-allowed.rs:125:34 + --> $DIR/where-allowed.rs:123:34 | LL | fn in_trait_impl_return() -> impl Debug { () } | ^^^^^^^^^^ @@ -176,127 +164,127 @@ LL | fn in_trait_impl_return() -> impl Debug { () } = help: add `#![feature(return_position_impl_trait_in_trait)]` to the crate attributes to enable error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `extern fn` param - --> $DIR/where-allowed.rs:138:33 + --> $DIR/where-allowed.rs:136:33 | LL | fn in_foreign_parameters(_: impl Debug); | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `extern fn` return - --> $DIR/where-allowed.rs:141:31 + --> $DIR/where-allowed.rs:139:31 | LL | fn in_foreign_return() -> impl Debug; | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `fn` pointer return - --> $DIR/where-allowed.rs:157:39 + --> $DIR/where-allowed.rs:155:39 | LL | type InReturnInTypeAlias = fn() -> impl Debug; | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in trait - --> $DIR/where-allowed.rs:162:16 + --> $DIR/where-allowed.rs:160:16 | LL | impl PartialEq for () { | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:167:24 + --> $DIR/where-allowed.rs:165:24 | LL | impl PartialEq<()> for impl Debug { | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:172:6 + --> $DIR/where-allowed.rs:170:6 | LL | impl impl Debug { | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:178:24 + --> $DIR/where-allowed.rs:176:24 | LL | impl InInherentImplAdt { | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:184:11 + --> $DIR/where-allowed.rs:182:11 | LL | where impl Debug: Debug | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:191:15 + --> $DIR/where-allowed.rs:189:15 | LL | where Vec: Debug | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in bound - --> $DIR/where-allowed.rs:198:24 + --> $DIR/where-allowed.rs:196:24 | LL | where T: PartialEq | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait param - --> $DIR/where-allowed.rs:205:17 + --> $DIR/where-allowed.rs:203:17 | LL | where T: Fn(impl Debug) | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in `Fn` trait return - --> $DIR/where-allowed.rs:212:22 + --> $DIR/where-allowed.rs:210:22 | LL | where T: Fn() -> impl Debug | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:218:40 + --> $DIR/where-allowed.rs:216:40 | LL | struct InStructGenericParamDefault(T); | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:222:36 + --> $DIR/where-allowed.rs:220:36 | LL | enum InEnumGenericParamDefault { Variant(T) } | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:226:38 + --> $DIR/where-allowed.rs:224:38 | LL | trait InTraitGenericParamDefault {} | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:230:41 + --> $DIR/where-allowed.rs:228:41 | LL | type InTypeAliasGenericParamDefault = T; | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:234:11 + --> $DIR/where-allowed.rs:232:11 | LL | impl T {} | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in type - --> $DIR/where-allowed.rs:241:40 + --> $DIR/where-allowed.rs:239:40 | LL | fn in_method_generic_param_default(_: T) {} | ^^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in variable binding - --> $DIR/where-allowed.rs:247:29 + --> $DIR/where-allowed.rs:245:29 | LL | let _in_local_variable: impl Fn() = || {}; | ^^^^^^^^^ error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in closure return - --> $DIR/where-allowed.rs:249:46 + --> $DIR/where-allowed.rs:247:46 | LL | let _in_return_in_local_variable = || -> impl Fn() { || {} }; | ^^^^^^^^^ error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions - --> $DIR/where-allowed.rs:234:7 + --> $DIR/where-allowed.rs:232:7 | LL | impl T {} | ^^^^^^^^^^^^^^ @@ -306,7 +294,7 @@ LL | impl T {} = note: `#[deny(invalid_type_param_default)]` on by default error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions - --> $DIR/where-allowed.rs:241:36 + --> $DIR/where-allowed.rs:239:36 | LL | fn in_method_generic_param_default(_: T) {} | ^^^^^^^^^^^^^^ @@ -315,14 +303,14 @@ LL | fn in_method_generic_param_default(_: T) {} = note: for more information, see issue #36887 error[E0118]: no nominal type found for inherent implementation - --> $DIR/where-allowed.rs:234:23 + --> $DIR/where-allowed.rs:232:23 | LL | impl T {} | ^ impl requires a nominal type | = note: either implement a trait on it or create a newtype to wrap it instead -error: aborting due to 49 previous errors +error: aborting due to 47 previous errors Some errors have detailed explanations: E0118, E0562, E0658, E0666. For more information about an error, try `rustc --explain E0118`.