Error code E0794 for late-bound lifetime parameter error. #107416
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Some changes occurred in diagnostic error codes |
| A lifetime parameter of a function definition is called *late-bound* if it both: | ||
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| 1. appears in an argument type | ||
| 2. does not appear in a where clause |
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I think it would be better to talk about not appearing in "a generic type constraint" rather than in "a where clause", as the 'a lifetime parameters in both fn<'a, T: Trait<'a>>(t: T) and fn<'a>(t: impl Trait<'a>) are early bound without there being any where clause.
| function of a concrete type by substituting concrete types for | ||
| generic ones, you cannot specify a late-bound lifetime, because such lifetime | ||
| parameters are resolved at the function's call site(s). |
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| function of a concrete type by substituting concrete types for | |
| generic ones, you cannot specify a late-bound lifetime, because such lifetime | |
| parameters are resolved at the function's call site(s). | |
| concrete instance of the generic function, you cannot specify any of | |
| its late-bound lifetime parameters, because they are not resolved until | |
| each call site(s). |
| ``` | ||
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| Lifetime parameters that are not late-bound are called *early-bound*. | ||
| The confusion might stem from the fact that late-bound and early-bound |
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| The confusion might stem from the fact that late-bound and early-bound | |
| Confusion may arise from the fact that late-bound and early-bound |
| In the definition of `bar`, the lifetime parameter `'a` is late-bound, while | ||
| `'b` is early-bound. This is reflected in the type annotation for `bar_fn`, | ||
| where `'a` is universally quantified and `'b` is substituted by a specific | ||
| lifetime. |
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| lifetime. | |
| lifetime. It is not possible to explicitly specify early-bound lifetime | |
| parameters when late-bound parameters are present, although the types | |
| that are constrained by early-bound parameters can be specified (as in the | |
| example above). |
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Is this what you mean? https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=c30a35a698a82969827f8260139c0f9d
It is possible in the sense that it just generates a warning, but warns about it being an error in the future.
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Apologies, only just saw your comment (the trials and tribulations of GitHub mobile!). Yes, _bar_fn2 in your playground is what I meant—a number of the tests output the error message "cannot specify lifetime arguments explicitly if late bound lifetime parameters are present", but I didn't appreciate they were only warnings (which compiletest denies/upgrades to errors); I think it'd still be helpful to make some reference to it?
That _bar_fn3 in your playground compiles is completely consistent with your existing explanation: no attempt was made to (erroneously) specify concrete lifetimes for late-bound parameters in a function reference, nor was the function reference cast to a pointer that would require explicit universal quantification; lifetime parameter 'b is early-bound to the lifetime parameter of the second argument, whatever that ends up happening to be—it is existentially, not universally, quantified.
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I think it's a shame to have lost the |
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@eggyal I agree, but I was unsure whether it fit the error code template while not being too lengthy. |
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☔ The latest upstream changes (presumably #102513) made this pull request unmergeable. Please resolve the merge conflicts. |
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Looks good to me and it's ok to add it back even if it's lengthy. |
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☔ The latest upstream changes (presumably #108488) made this pull request unmergeable. Please resolve the merge conflicts. |
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Bump. Is anything more needed? @GuillaumeGomez @WaffleLapkin |
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No nothing. Sorry, completely forgot about it. Thanks for working on this! @bors r+ rollup |
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Error code E0794 for late-bound lifetime parameter error. This PR addresses [rust-lang#80618](rust-lang#80618).
…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#107416 (Error code E0794 for late-bound lifetime parameter error.) - rust-lang#108772 (Speed up tidy quite a lot) - rust-lang#109193 (Add revisions for -Zlower-impl-trait-in-trait-to-assoc-ty fixed tests) - rust-lang#109234 (Tweak implementation of overflow checking assertions) - rust-lang#109238 (Fix generics mismatch errors for RPITITs on -Zlower-impl-trait-in-trait-to-assoc-ty) - rust-lang#109283 (rustdoc: reduce allocations in `visibility_to_src_with_space`) - rust-lang#109287 (Use `size_of_val` instead of manual calculation) - rust-lang#109288 (Stabilise `unix_socket_abstract`) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
This PR addresses #80618.