diff options
| -rw-r--r-- | src/librustc/infer/opaque_types/mod.rs | 5 | ||||
| -rw-r--r-- | src/librustc_typeck/check/mod.rs | 111 | ||||
| -rw-r--r-- | src/test/ui/impl-trait/where-allowed-2.rs | 9 | ||||
| -rw-r--r-- | src/test/ui/impl-trait/where-allowed-2.stderr | 11 | ||||
| -rw-r--r-- | src/test/ui/impl-trait/where-allowed.rs | 5 | ||||
| -rw-r--r-- | src/test/ui/impl-trait/where-allowed.stderr | 102 | ||||
| -rw-r--r-- | src/test/ui/type-alias-impl-trait/fallback.rs | 28 |
7 files changed, 205 insertions, 66 deletions
diff --git a/src/librustc/infer/opaque_types/mod.rs b/src/librustc/infer/opaque_types/mod.rs index 9ed60b1f0c1..9b197c1ecb1 100644 --- a/src/librustc/infer/opaque_types/mod.rs +++ b/src/librustc/infer/opaque_types/mod.rs @@ -24,6 +24,10 @@ pub type OpaqueTypeMap<'tcx> = DefIdMap<OpaqueTypeDecl<'tcx>>; /// appear in the return type). #[derive(Copy, Clone, Debug)] pub struct OpaqueTypeDecl<'tcx> { + + /// The opaque type (`ty::Opaque`) for this declaration. + pub opaque_type: Ty<'tcx>, + /// The substitutions that we apply to the opaque type that this /// `impl Trait` desugars to. e.g., if: /// @@ -1150,6 +1154,7 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> { self.opaque_types.insert( def_id, OpaqueTypeDecl { + opaque_type: ty, substs, definition_span, concrete_ty: ty_var, diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs index a8418c5f349..50c1a74fe91 100644 --- a/src/librustc_typeck/check/mod.rs +++ b/src/librustc_typeck/check/mod.rs @@ -147,7 +147,7 @@ use crate::TypeAndSubsts; use crate::lint; use crate::util::captures::Captures; use crate::util::common::{ErrorReported, indenter}; -use crate::util::nodemap::{DefIdMap, DefIdSet, FxHashSet, HirIdMap}; +use crate::util::nodemap::{DefIdMap, DefIdSet, FxHashMap, FxHashSet, HirIdMap}; pub use self::Expectation::*; use self::autoderef::Autoderef; @@ -231,6 +231,13 @@ pub struct Inherited<'a, 'tcx> { // 'de-opaque' OpaqueTypeDecl, after typeck is done with all functions. opaque_types: RefCell<DefIdMap<OpaqueTypeDecl<'tcx>>>, + /// A map from inference variables created from opaque + /// type instantiations (`ty::Infer`) to the actual opaque + /// type (`ty::Opaque`). Used during fallback to map unconstrained + /// opaque type inference variables to their corresponding + /// opaque type. + opaque_types_vars: RefCell<FxHashMap<Ty<'tcx>, Ty<'tcx>>>, + /// Each type parameter has an implicit region bound that /// indicates it must outlive at least the function body (the user /// may specify stronger requirements). This field indicates the @@ -696,6 +703,7 @@ impl Inherited<'a, 'tcx> { deferred_cast_checks: RefCell::new(Vec::new()), deferred_generator_interiors: RefCell::new(Vec::new()), opaque_types: RefCell::new(Default::default()), + opaque_types_vars: RefCell::new(Default::default()), implicit_region_bound, body_id, } @@ -937,9 +945,46 @@ fn typeck_tables_of(tcx: TyCtxt<'_>, def_id: DefId) -> &ty::TypeckTables<'_> { // All type checking constraints were added, try to fallback unsolved variables. fcx.select_obligations_where_possible(false, |_| {}); let mut fallback_has_occurred = false; + + // We do fallback in two passes, to try to generate + // better error messages. + // The first time, we do *not* replace opaque types. for ty in &fcx.unsolved_variables() { - fallback_has_occurred |= fcx.fallback_if_possible(ty); + fallback_has_occurred |= fcx.fallback_if_possible(ty, FallbackMode::NoOpaque); + } + // We now see if we can make progress. This might + // cause us to unify inference variables for opaque types, + // since we may have unified some other type variables + // during the first phase of fallback. + // This means that we only replace inference variables with their underlying + // opaque types as a last resort. + // + // In code like this: + // + // ```rust + // type MyType = impl Copy; + // fn produce() -> MyType { true } + // fn bad_produce() -> MyType { panic!() } + // ``` + // + // we want to unify the opaque inference variable in `bad_produce` + // with the diverging fallback for `panic!` (e.g. `()` or `!`). + // This will produce a nice error message about conflicting concrete + // types for `MyType`. + // + // If we had tried to fallback the opaque inference variable to `MyType`, + // we will generate a confusing type-check error that does not explicitly + // refer to opaque types. + fcx.select_obligations_where_possible(fallback_has_occurred, |_| {}); + + // We now run fallback again, but this time we allow it to replace + // unconstrained opaque type variables, in addition to performing + // other kinds of fallback. + for ty in &fcx.unsolved_variables() { + fallback_has_occurred |= fcx.fallback_if_possible(ty, FallbackMode::All); } + + // See if we can make any more progress. fcx.select_obligations_where_possible(fallback_has_occurred, |_| {}); // Even though coercion casts provide type hints, we check casts after fallback for @@ -2499,6 +2544,16 @@ enum TupleArgumentsFlag { TupleArguments, } +/// Controls how we perform fallback for unconstrained +/// type variables. +enum FallbackMode { + /// Do not fallback type variables to opaque types. + NoOpaque, + /// Perform all possible kinds of fallback, including + /// turning type variables to opaque types. + All, +} + impl<'a, 'tcx> FnCtxt<'a, 'tcx> { pub fn new( inh: &'a Inherited<'a, 'tcx>, @@ -2864,8 +2919,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { ); let mut opaque_types = self.opaque_types.borrow_mut(); + let mut opaque_types_vars = self.opaque_types_vars.borrow_mut(); for (ty, decl) in opaque_type_map { let _ = opaque_types.insert(ty, decl); + let _ = opaque_types_vars.insert(decl.concrete_ty, decl.opaque_type); } value @@ -3078,7 +3135,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { // Fallback becomes very dubious if we have encountered type-checking errors. // In that case, fallback to Error. // The return value indicates whether fallback has occurred. - fn fallback_if_possible(&self, ty: Ty<'tcx>) -> bool { + fn fallback_if_possible(&self, ty: Ty<'tcx>, mode: FallbackMode) -> bool { use rustc::ty::error::UnconstrainedNumeric::Neither; use rustc::ty::error::UnconstrainedNumeric::{UnconstrainedInt, UnconstrainedFloat}; @@ -3088,7 +3145,53 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { UnconstrainedInt => self.tcx.types.i32, UnconstrainedFloat => self.tcx.types.f64, Neither if self.type_var_diverges(ty) => self.tcx.mk_diverging_default(), - Neither => return false, + Neither => { + // This type variable was created from the instantiation of an opaque + // type. The fact that we're attempting to perform fallback for it + // means that the function neither constrained it to a concrete + // type, nor to the opaque type itself. + // + // For example, in this code: + // + //``` + // type MyType = impl Copy; + // fn defining_use() -> MyType { true } + // fn other_use() -> MyType { defining_use() } + // ``` + // + // `defining_use` will constrain the instantiated inference + // variable to `bool`, while `other_use` will constrain + // the instantiated inference variable to `MyType`. + // + // When we process opaque types during writeback, we + // will handle cases like `other_use`, and not count + // them as defining usages + // + // However, we also need to handle cases like this: + // + // ```rust + // pub type Foo = impl Copy; + // fn produce() -> Option<Foo> { + // None + // } + // ``` + // + // In the above snippet, the inference varaible created by + // instantiating `Option<Foo>` will be completely unconstrained. + // We treat this as a non-defining use by making the inference + // variable fall back to the opaque type itself. + if let FallbackMode::All = mode { + if let Some(opaque_ty) = self.opaque_types_vars.borrow().get(ty) { + debug!("fallback_if_possible: falling back opaque type var {:?} to {:?}", + ty, opaque_ty); + *opaque_ty + } else { + return false; + } + } else { + return false; + } + }, }; debug!("fallback_if_possible: defaulting `{:?}` to `{:?}`", ty, fallback); self.demand_eqtype(syntax_pos::DUMMY_SP, ty, fallback); diff --git a/src/test/ui/impl-trait/where-allowed-2.rs b/src/test/ui/impl-trait/where-allowed-2.rs new file mode 100644 index 00000000000..f7744ef1b3e --- /dev/null +++ b/src/test/ui/impl-trait/where-allowed-2.rs @@ -0,0 +1,9 @@ +//! Ideally, these tests would go in `where-allowed.rs`, but we bail out +//! too early to display them. +use std::fmt::Debug; + +// Disallowed +fn in_adt_in_return() -> Vec<impl Debug> { panic!() } +//~^ ERROR opaque type expands to a recursive type + +fn main() {} diff --git a/src/test/ui/impl-trait/where-allowed-2.stderr b/src/test/ui/impl-trait/where-allowed-2.stderr new file mode 100644 index 00000000000..1de15014c1f --- /dev/null +++ b/src/test/ui/impl-trait/where-allowed-2.stderr @@ -0,0 +1,11 @@ +error[E0720]: opaque type expands to a recursive type + --> $DIR/where-allowed-2.rs:6:30 + | +LL | fn in_adt_in_return() -> Vec<impl Debug> { panic!() } + | ^^^^^^^^^^ expands to a recursive type + | + = note: type resolves to itself + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0720`. diff --git a/src/test/ui/impl-trait/where-allowed.rs b/src/test/ui/impl-trait/where-allowed.rs index 5ab74e02e0e..211a14ed4dd 100644 --- a/src/test/ui/impl-trait/where-allowed.rs +++ b/src/test/ui/impl-trait/where-allowed.rs @@ -12,10 +12,6 @@ fn in_return() -> impl Debug { panic!() } fn in_adt_in_parameters(_: Vec<impl Debug>) { panic!() } // Disallowed -fn in_adt_in_return() -> Vec<impl Debug> { panic!() } -//~^ ERROR type annotations needed - -// Disallowed fn in_fn_parameter_in_parameters(_: fn(impl Debug)) { panic!() } //~^ ERROR `impl Trait` not allowed outside of function and inherent method return types @@ -60,7 +56,6 @@ fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() } fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() } //~^ ERROR `impl Trait` not allowed outside of function and inherent method return types //~| ERROR nested `impl Trait` is not allowed -//~| ERROR type annotations needed // Disallowed fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { panic!() } diff --git a/src/test/ui/impl-trait/where-allowed.stderr b/src/test/ui/impl-trait/where-allowed.stderr index fcd4c357afd..e5d2feff51c 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:51:51 + --> $DIR/where-allowed.rs:47:51 | 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:60:57 + --> $DIR/where-allowed.rs:56:57 | 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:124:16 + --> $DIR/where-allowed.rs:119:16 | 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:160:23 + --> $DIR/where-allowed.rs:155:23 | LL | type InTypeAlias<R> = impl Debug; | ^^^^^^^^^^ @@ -35,7 +35,7 @@ LL | type InTypeAlias<R> = 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:164:39 + --> $DIR/where-allowed.rs:159:39 | LL | type InReturnInTypeAlias<R> = fn() -> impl Debug; | ^^^^^^^^^^ @@ -44,205 +44,205 @@ LL | type InReturnInTypeAlias<R> = fn() -> impl Debug; = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:19:40 + --> $DIR/where-allowed.rs:15:40 | LL | fn in_fn_parameter_in_parameters(_: fn(impl Debug)) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:23:42 + --> $DIR/where-allowed.rs:19:42 | LL | fn in_fn_return_in_parameters(_: fn() -> impl Debug) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:27:38 + --> $DIR/where-allowed.rs:23:38 | LL | fn in_fn_parameter_in_return() -> fn(impl Debug) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:31:40 + --> $DIR/where-allowed.rs:27:40 | LL | fn in_fn_return_in_return() -> fn() -> impl Debug { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:35:49 + --> $DIR/where-allowed.rs:31:49 | LL | fn in_dyn_Fn_parameter_in_parameters(_: &dyn Fn(impl Debug)) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:39:51 + --> $DIR/where-allowed.rs:35:51 | LL | fn in_dyn_Fn_return_in_parameters(_: &dyn Fn() -> impl Debug) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:43:55 + --> $DIR/where-allowed.rs:39:55 | LL | fn in_dyn_Fn_parameter_in_return() -> &'static dyn Fn(impl Debug) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:47:57 + --> $DIR/where-allowed.rs:43:57 | LL | fn in_dyn_Fn_return_in_return() -> &'static dyn Fn() -> impl Debug { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:51:51 + --> $DIR/where-allowed.rs:47:51 | LL | fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:56:53 + --> $DIR/where-allowed.rs:52:53 | LL | fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:60:57 + --> $DIR/where-allowed.rs:56:57 | LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:66:59 + --> $DIR/where-allowed.rs:61:59 | LL | fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:70:38 + --> $DIR/where-allowed.rs:65:38 | LL | fn in_Fn_parameter_in_generics<F: Fn(impl Debug)> (_: F) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:74:40 + --> $DIR/where-allowed.rs:69:40 | LL | fn in_Fn_return_in_generics<F: Fn() -> impl Debug> (_: F) { panic!() } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:87:32 + --> $DIR/where-allowed.rs:82:32 | LL | struct InBraceStructField { x: impl Debug } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:91:41 + --> $DIR/where-allowed.rs:86:41 | LL | struct InAdtInBraceStructField { x: Vec<impl Debug> } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:95:27 + --> $DIR/where-allowed.rs:90:27 | LL | struct InTupleStructField(impl Debug); | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:100:25 + --> $DIR/where-allowed.rs:95:25 | LL | InBraceVariant { x: impl Debug }, | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:102:20 + --> $DIR/where-allowed.rs:97:20 | LL | InTupleVariant(impl Debug), | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:113:23 + --> $DIR/where-allowed.rs:108:23 | LL | fn in_return() -> impl Debug; | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:131:34 + --> $DIR/where-allowed.rs:126:34 | LL | fn in_trait_impl_return() -> impl Debug { () } | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:144:33 + --> $DIR/where-allowed.rs:139:33 | LL | fn in_foreign_parameters(_: impl Debug); | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:147:31 + --> $DIR/where-allowed.rs:142:31 | LL | fn in_foreign_return() -> impl Debug; | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:164:39 + --> $DIR/where-allowed.rs:159:39 | LL | type InReturnInTypeAlias<R> = fn() -> impl Debug; | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:169:16 + --> $DIR/where-allowed.rs:164:16 | LL | impl PartialEq<impl Debug> for () { | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:174:24 + --> $DIR/where-allowed.rs:169:24 | LL | impl PartialEq<()> for impl Debug { | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:179:6 + --> $DIR/where-allowed.rs:174:6 | LL | impl impl Debug { | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:185:24 + --> $DIR/where-allowed.rs:180:24 | LL | impl InInherentImplAdt<impl Debug> { | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:191:11 + --> $DIR/where-allowed.rs:186:11 | LL | where impl Debug: Debug | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:198:15 + --> $DIR/where-allowed.rs:193:15 | LL | where Vec<impl Debug>: Debug | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:205:24 + --> $DIR/where-allowed.rs:200:24 | LL | where T: PartialEq<impl Debug> | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:212:17 + --> $DIR/where-allowed.rs:207:17 | LL | where T: Fn(impl Debug) | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:219:22 + --> $DIR/where-allowed.rs:214:22 | LL | where T: Fn() -> impl Debug | ^^^^^^^^^^ error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:225:29 + --> $DIR/where-allowed.rs:220:29 | LL | let _in_local_variable: impl Fn() = || {}; | ^^^^^^^^^ @@ -250,36 +250,24 @@ LL | let _in_local_variable: impl Fn() = || {}; = help: add `#![feature(impl_trait_in_bindings)]` to the crate attributes to enable error[E0562]: `impl Trait` not allowed outside of function and inherent method return types - --> $DIR/where-allowed.rs:227:46 + --> $DIR/where-allowed.rs:222:46 | LL | let _in_return_in_local_variable = || -> impl Fn() { || {} }; | ^^^^^^^^^ -error[E0282]: type annotations needed - --> $DIR/where-allowed.rs:15:30 - | -LL | fn in_adt_in_return() -> Vec<impl Debug> { panic!() } - | ^^^^^^^^^^ cannot infer type - -error[E0282]: type annotations needed - --> $DIR/where-allowed.rs:60:49 - | -LL | fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() } - | ^^^^^^^^^^^^^^^^^^^ cannot infer type - error: could not find defining uses - --> $DIR/where-allowed.rs:160:1 + --> $DIR/where-allowed.rs:155:1 | LL | type InTypeAlias<R> = impl Debug; | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: could not find defining uses - --> $DIR/where-allowed.rs:124:5 + --> $DIR/where-allowed.rs:119:5 | LL | type Out = impl Debug; | ^^^^^^^^^^^^^^^^^^^^^^ -error: aborting due to 44 previous errors +error: aborting due to 42 previous errors -Some errors have detailed explanations: E0282, E0562, E0658, E0666. -For more information about an error, try `rustc --explain E0282`. +Some errors have detailed explanations: E0562, E0658, E0666. +For more information about an error, try `rustc --explain E0562`. diff --git a/src/test/ui/type-alias-impl-trait/fallback.rs b/src/test/ui/type-alias-impl-trait/fallback.rs new file mode 100644 index 00000000000..fe1ca2230da --- /dev/null +++ b/src/test/ui/type-alias-impl-trait/fallback.rs @@ -0,0 +1,28 @@ +// Tests that we correctly handle the instantiated +// inference variable being completely unconstrained. +// +// check-pass +#![feature(type_alias_impl_trait)] + +type Foo = impl Copy; + +enum Wrapper<T> { + First(T), + Second +} + +// This method constrains `Foo` to be `bool` +fn constrained_foo() -> Foo { + true +} + + +// This method does not constrain `Foo`. +// Per RFC 2071, function bodies may either +// fully constrain an opaque type, or place no +// constraints on it. +fn unconstrained_foo() -> Wrapper<Foo> { + Wrapper::Second +} + +fn main() {} |