c3205f98dd
Removes the attribute from `MetaSized` and `PointeeSized`, with a special case in the trait solvers for `MetaSized`. `dyn MetaSized` is a perfectly cromulent type, and seems to only have had #[rustc_do_not_implement_via_object] so the builtin object candidate does not overlap with the builtin MetaSized impl that all `dyn` types get. Resolves this with a special case by checking `is_sizedness_trait` where the trait solvers previously checked `implement_via_object`. `dyn PointeeSized` alone is rejected for other reasons (since `dyn PointeeSized` is considered to have no principal trait because `PointeeSized` is removed at an earlier stage of the compiler), but `(dyn PointeeSized + Send)` is valid and equivalent to `dyn Send`. Add suggestions from code review Update compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs and tests Co-authored-by: lcnr <rust@lcnr.de>
25 lines
665 B
Rust
25 lines
665 B
Rust
//@ run-pass
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//! This test and `sized-*.rs` and `pointeesized.rs` test that dyn-compatibility correctly
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//! handles sizedness traits, which are special in several parts of the compiler.
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#![feature(sized_hierarchy)]
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use std::marker::MetaSized;
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trait Foo: std::fmt::Debug + MetaSized {}
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impl<T: std::fmt::Debug + MetaSized> Foo for T {}
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fn unsize_sized<T: 'static>(x: Box<T>) -> Box<dyn MetaSized> {
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x
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}
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fn unsize_subtrait(x: Box<dyn Foo>) -> Box<dyn MetaSized> {
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x
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}
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fn main() {
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let _bx = unsize_sized(Box::new(vec![1, 2, 3]));
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let bx: Box<dyn Foo> = Box::new(vec![1, 2, 3]);
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let _ = format!("{bx:?}");
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let _bx = unsize_subtrait(bx);
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}
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