Define coherence restrictions in the manual impl section. #9743
Comments
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Triage: coherence is per-crate, since the compiler sees the whole crate at once (and so can reason about that). Answers (if someone wishes to take this on):
Yes,
Yes, that's fine, since coherence is per-crate. |
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This seems like a sub-bug of #11166 to me... |
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@pnkfelix pointed out that I'd accidentally said "coherence is per-module" originally; fixed now. |
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I'm just going to close this in favor of that one. |
flip1995
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…=Alexendoo
Improve `needless_lifetimes`
This PR makes the following improvements to `needless_lifetimes`.
* It fixes the following false negative, where `foo` is flagged but `bar` is not:
```rust
fn foo<'a>(x: &'a u8, y: &'_ u8) {}
fn bar<'a>(x: &'a u8, y: &'_ u8, z: &'_ u8) {}
```
* It flags more cases, generally. Previously, `needless_borrow` required *all* lifetimes to be used only once. With the changes, individual lifetimes are flagged for being used only once, even if not all lifetimes are.
* Finally, it tries to produce more clear error messages.
changelog: fix `needless_lifetimes` false negative involving functions with multiple unnamed lifetimes
changelog: in `needless_lifetimes`, flag individual lifetimes used only once, rather than require all lifetimes to be used only once
changelog: in `needless_lifetimes`, emit "replace with `'_`" warnings only when applicable, and point to a generic argument
flip1995
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Dec 1, 2022
…ndoo Use `walk_generic_arg` This is a tiny followup to to rust-lang#9743, now that rust-lang#103692 has landed. r? `@Alexendoo` changelog: none
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I'm familiar with coherence restrictions on trait impls only from IRC conversations ages ago. It came up in IRC again, and I briefly skimmed the manual sections on impls and crates to see if this restriction was spelled out.
I may have missed it. Even in that case, I feel it would be most useful in the manual section describing impls: 6.1.9 Implementations (v0.8 manual)
pcwalton has a good blog post providing background: Coherence, Modularity, and Extensibility for Typeclasses
There was some confusion on IRC as to whether coherence restrictions are per-module or per-crate.
Some questions I'd like to see answered in the manual:
A, and an impl in another moduleBcoherently?The text was updated successfully, but these errors were encountered: