1 files changed, 251 insertions, 0 deletions
diff --git a/src/test/ui/impl-trait/where-allowed.rs b/src/test/ui/impl-trait/where-allowed.rs
new file mode 100644
index 000000000..c1dd46c7f
--- /dev/null
+++ b/src/test/ui/impl-trait/where-allowed.rs
@@ -0,0 +1,251 @@
+//! A simple test for testing many permutations of allowedness of
+//! impl Trait
+use std::fmt::Debug;
+
+// Allowed
+fn in_parameters(_: impl Debug) { panic!() }
+
+// Allowed
+fn in_return() -> impl Debug { panic!() }
+
+// Allowed
+fn in_adt_in_parameters(_: Vec<impl Debug>) { panic!() }
+
+// Disallowed
+fn in_fn_parameter_in_parameters(_: fn(impl Debug)) { panic!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+fn in_fn_return_in_parameters(_: fn() -> impl Debug) { panic!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+fn in_fn_parameter_in_return() -> fn(impl Debug) { panic!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+fn in_fn_return_in_return() -> fn() -> impl Debug { panic!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+fn in_dyn_Fn_parameter_in_parameters(_: &dyn Fn(impl Debug)) { panic!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+fn in_dyn_Fn_return_in_parameters(_: &dyn Fn() -> impl Debug) { panic!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+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
+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!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+//~^^ ERROR nested `impl Trait` is not allowed
+
+// Disallowed
+fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+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
+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: Fn(impl Debug)> (_: F) { panic!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+fn in_Fn_return_in_generics<F: Fn() -> impl Debug> (_: F) { panic!() }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+
+// Allowed
+fn in_impl_Trait_in_parameters(_: impl Iterator<Item = impl Iterator>) { panic!() }
+
+// Allowed
+fn in_impl_Trait_in_return() -> impl IntoIterator<Item = impl IntoIterator> {
+    vec![vec![0; 10], vec![12; 7], vec![8; 3]]
+}
+
+// Disallowed
+struct InBraceStructField { x: impl Debug }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+struct InAdtInBraceStructField { x: Vec<impl Debug> }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+struct InTupleStructField(impl Debug);
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+enum InEnum {
+    InBraceVariant { x: impl Debug },
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+    InTupleVariant(impl Debug),
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+}
+
+// Allowed
+trait InTraitDefnParameters {
+    fn in_parameters(_: impl Debug);
+}
+
+// Disallowed
+trait InTraitDefnReturn {
+    fn in_return() -> impl Debug;
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+}
+
+// Allowed and disallowed in trait impls
+trait DummyTrait {
+    type Out;
+    fn in_trait_impl_parameter(_: impl Debug);
+    fn in_trait_impl_return() -> Self::Out;
+}
+impl DummyTrait for () {
+    type Out = impl Debug;
+    //~^ ERROR `impl Trait` in type aliases is unstable
+
+    fn in_trait_impl_parameter(_: impl Debug) { }
+    // Allowed
+
+    fn in_trait_impl_return() -> impl Debug { () }
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+}
+
+// Allowed
+struct DummyType;
+impl DummyType {
+    fn in_inherent_impl_parameters(_: impl Debug) { }
+    fn in_inherent_impl_return() -> impl Debug { () }
+}
+
+// Disallowed
+extern "C" {
+    fn in_foreign_parameters(_: impl Debug);
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+    fn in_foreign_return() -> impl Debug;
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+}
+
+// Allowed
+extern "C" fn in_extern_fn_parameters(_: impl Debug) {
+}
+
+// Allowed
+extern "C" fn in_extern_fn_return() -> impl Debug {
+    22
+}
+
+type InTypeAlias<R> = impl Debug;
+//~^ ERROR `impl Trait` in type aliases is unstable
+
+type InReturnInTypeAlias<R> = fn() -> impl Debug;
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+//~| ERROR `impl Trait` in type aliases is unstable
+
+// Disallowed in impl headers
+impl PartialEq<impl Debug> for () {
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+}
+
+// Disallowed in impl headers
+impl PartialEq<()> for impl Debug {
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+}
+
+// Disallowed in inherent impls
+impl impl Debug {
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+}
+
+// Disallowed in inherent impls
+struct InInherentImplAdt<T> { t: T }
+impl InInherentImplAdt<impl Debug> {
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+}
+
+// Disallowed in where clauses
+fn in_fn_where_clause()
+    where impl Debug: Debug
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+{
+}
+
+// Disallowed in where clauses
+fn in_adt_in_fn_where_clause()
+    where Vec<impl Debug>: Debug
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+{
+}
+
+// Disallowed
+fn in_trait_parameter_in_fn_where_clause<T>()
+    where T: PartialEq<impl Debug>
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+{
+}
+
+// Disallowed
+fn in_Fn_parameter_in_fn_where_clause<T>()
+    where T: Fn(impl Debug)
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+{
+}
+
+// Disallowed
+fn in_Fn_return_in_fn_where_clause<T>()
+    where T: Fn() -> impl Debug
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+{
+}
+
+// Disallowed
+struct InStructGenericParamDefault<T = impl Debug>(T);
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+enum InEnumGenericParamDefault<T = impl Debug> { Variant(T) }
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+trait InTraitGenericParamDefault<T = impl Debug> {}
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+type InTypeAliasGenericParamDefault<T = impl Debug> = T;
+//~^ ERROR `impl Trait` only allowed in function and inherent method return types
+
+// Disallowed
+impl <T = impl Debug> T {}
+//~^ ERROR defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
+//~| WARNING this was previously accepted by the compiler but is being phased out
+//~| ERROR `impl Trait` only allowed in function and inherent method return types
+//~| ERROR no nominal type found
+
+// Disallowed
+fn in_method_generic_param_default<T = impl Debug>(_: T) {}
+//~^ ERROR defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
+//~| WARNING this was previously accepted by the compiler but is being phased out
+//~| ERROR `impl Trait` only allowed in function and inherent method return types
+
+fn main() {
+    let _in_local_variable: impl Fn() = || {};
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+    let _in_return_in_local_variable = || -> impl Fn() { || {} };
+    //~^ ERROR `impl Trait` only allowed in function and inherent method return types
+}