orphan check: rationalize our handling of constants #99861
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| // All possible values for a constant parameter already exist | ||
| // in the crate defining the trait, so they are always non-local. |
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Hmm is const Foo: &dyn Bar ever even possible? What about <T: Trait, const Foo: T>?
I think this statement holds today, but if it could ever change in the future, do we have some way to ensure we don't forget about this?
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T: Trait, const VALUE: T isn't an issue, because T has to be forward declared, so if T is a local type, then the orphan check already succeeds the moment it sees T
for trait objects that's more difficult 😁 or well, it depends on whether we already have local values for const T: fn(). going to extend that comment.
feel like the value of allowing uncovered const params is still greater then allowing impls to be guarded by a local function pointer 😁 so this impl is still the right one imo
| extern crate trait_with_const_param; | ||
| use trait_with_const_param::*; | ||
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| // Trivial case, const param after local type. |
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Wrong description? "Impl for local type"?
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in the substs of that impl trait ref we have [Local1, N, T], so const param after local type holds 😁
want me to change that comment? don't think that "impl for local type" is the right descr because the same also holds for impl<const N: usize, T> OtherTrait<Local1, N, T> for ForeignTy
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@bors r+ |
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Rollup of 6 pull requests Successful merges: - rust-lang#99582 (Delay a span bug if we see ty/const generic params during writeback) - rust-lang#99861 (orphan check: rationalize our handling of constants) - rust-lang#100026 (Add `Iterator::array_chunks` (take N+1)) - rust-lang#100115 (Suggest removing `let` if `const let` or `let const` is used) - rust-lang#100126 (rustc_target: Update some old naming around self contained linking) - rust-lang#100487 (`assert_{inhabited,zero_valid,uninit_valid}` intrinsics are safe) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
cc @rust-lang/types @rust-lang/project-const-generics on whether you agree with this reasoning.
r? types