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Regression tests.

Update: incorporate review feedback.
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pnkfelix committed Sep 27, 2019
1 parent a18d424 commit e443e1bdf9f474f822008f88862fed630b50381f
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#![crate_type="lib"]

// rust-lang/rust#61631: The use of `Self` in the defaults of generic
// types in a *trait* definition are allowed.
//
// It *must* be accepted; we have used this pattern extensively since
// Rust 1.0 (see e.g. `trait Add<Rhs=Self>`).
trait Tnobound<P = Self> {}

impl Tnobound for () { }

// This variant is accepted at the definition site; but it will be
// rejected at every possible usage site (such as the one immediately
// below). Maybe one day we will attempt to catch it at the definition
// site, but today this is accepted due to compiler implementation
// limitations.
trait Tsized<P: Sized = [Self]> {}

impl Tsized for () {}
//~^ ERROR the size for values of type `[()]` cannot be known at compilation time [E0277]
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error[E0277]: the size for values of type `[()]` cannot be known at compilation time
--> $DIR/issue-61631-default-type-param-can-reference-self-in-trait.rs:19:6
|
LL | impl Tsized for () {}
| ^^^^^^ doesn't have a size known at compile-time
|
= help: the trait `std::marker::Sized` is not implemented for `[()]`
= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
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#![crate_type="lib"]

// rust-lang/rust#61631: Uses of `Self` in the defaults of generic
// types for ADT's are not allowed. We justify this because the `Self`
// type could be considered the "final" type parameter, that is only
// well-defined after all of the other type parameters on the ADT have
// been instantiated.
//
// These were previously were ICE'ing at the usage point anyway (see
// `demo_usages` below), so there should not be any backwards
// compatibility concern.

struct Snobound<'a, P = Self> { x: Option<&'a P> }
//~^ ERROR type parameters cannot use `Self` in their defaults [E0735]

enum Enobound<'a, P = Self> { A, B(Option<&'a P>) }
//~^ ERROR type parameters cannot use `Self` in their defaults [E0735]

union Unobound<'a, P = Self> { x: i32, y: Option<&'a P> }
//~^ ERROR type parameters cannot use `Self` in their defaults [E0735]

// Disallowing `Self` in defaults sidesteps need to check the bounds
// on the defaults in cases like these.

struct Ssized<'a, P: Sized = [Self]> { x: Option<&'a P> }
//~^ ERROR type parameters cannot use `Self` in their defaults [E0735]

enum Esized<'a, P: Sized = [Self]> { A, B(Option<&'a P>) }
//~^ ERROR type parameters cannot use `Self` in their defaults [E0735]

union Usized<'a, P: Sized = [Self]> { x: i32, y: Option<&'a P> }
//~^ ERROR type parameters cannot use `Self` in their defaults [E0735]

fn demo_usages() {
// An ICE means you only get the error from the first line of the
// demo; comment each out to observe the other ICEs when trying
// this out on older versions of Rust.

let _ice: Snobound;
let _ice: Enobound;
let _ice: Unobound;
let _ice: Ssized;
let _ice: Esized;
let _ice: Usized;
}
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error[E0735]: type parameters cannot use `Self` in their defaults
--> $DIR/issue-61631-default-type-param-cannot-reference-self.rs:13:25
|
LL | struct Snobound<'a, P = Self> { x: Option<&'a P> }
| ^^^^ `Self` in type parameter default

error[E0735]: type parameters cannot use `Self` in their defaults
--> $DIR/issue-61631-default-type-param-cannot-reference-self.rs:16:23
|
LL | enum Enobound<'a, P = Self> { A, B(Option<&'a P>) }
| ^^^^ `Self` in type parameter default

error[E0735]: type parameters cannot use `Self` in their defaults
--> $DIR/issue-61631-default-type-param-cannot-reference-self.rs:19:24
|
LL | union Unobound<'a, P = Self> { x: i32, y: Option<&'a P> }
| ^^^^ `Self` in type parameter default

error[E0735]: type parameters cannot use `Self` in their defaults
--> $DIR/issue-61631-default-type-param-cannot-reference-self.rs:25:31
|
LL | struct Ssized<'a, P: Sized = [Self]> { x: Option<&'a P> }
| ^^^^ `Self` in type parameter default

error[E0735]: type parameters cannot use `Self` in their defaults
--> $DIR/issue-61631-default-type-param-cannot-reference-self.rs:28:29
|
LL | enum Esized<'a, P: Sized = [Self]> { A, B(Option<&'a P>) }
| ^^^^ `Self` in type parameter default

error[E0735]: type parameters cannot use `Self` in their defaults
--> $DIR/issue-61631-default-type-param-cannot-reference-self.rs:31:30
|
LL | union Usized<'a, P: Sized = [Self]> { x: i32, y: Option<&'a P> }
| ^^^^ `Self` in type parameter default

error: aborting due to 6 previous errors

For more information about this error, try `rustc --explain E0735`.

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