Tweak lifetime definition errors #68267
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This doesn't mention that using an existing lifetime is possible, but that would hopefully be clear as always being an option. The intention of this is to teach newcomers what the lifetime syntax is.
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Tweak lifetime definition errors Taking inspiration from the narrative in @fasterthanlime's https://fasterthanli.me/blog/2019/declarative-memory-management/, add suggestions to some lifetime definition errors.
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eddyb
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| help: consider introducing a named lifetime parameter | ||
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| LL | struct Foo<'lifetime> { | ||
| LL | x: &'lifetime bool, |
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Couldn't this use 'a instead of 'lifetime, to be more realistic?
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It could, but we are also targeting people who might be just picking Rust up with these messages who might not know the meaning of 'a to begin with.
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It would be nicer to say that 'a is a lifetime somewhere in the diagnostic, than risk people copy-pasting the 'lifetime example literally into their code and getting the wrong impression that it's a convention.
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#68583 tackles this
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Account for HR lifetimes when suggesting introduction of named lifetime ``` error[E0106]: missing lifetime specifier --> src/test/ui/suggestions/fn-missing-lifetime-in-item.rs:2:32 | 2 | struct S2<F: Fn(&i32, &i32) -> &i32>(F); | ---- ---- ^ expected named lifetime parameter | = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from argument 1 or argument 2 = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html help: consider making the bound lifetime-generic with a new `'a` lifetime | 2 | struct S2<F: for<'a> Fn(&'a i32, &'a i32) -> &'a i32>(F); | ^^^^^^^ ^^^^^^^ ^^^^^^^ ^^^ help: consider introducing a named lifetime parameter | 2 | struct S2<'a, F: Fn(&'a i32, &'a i32) -> &'a i32>(F);= | ^^^ ^^^^^^^ ^^^^^^^ ^^^ ``` Follow up to rust-lang#68267. Addresses the diagnostics part of rust-lang#49287.
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Account for HR lifetimes when suggesting introduction of named lifetime ``` error[E0106]: missing lifetime specifier --> src/test/ui/suggestions/fn-missing-lifetime-in-item.rs:2:32 | 2 | struct S2<F: Fn(&i32, &i32) -> &i32>(F); | ---- ---- ^ expected named lifetime parameter | = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from argument 1 or argument 2 = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html help: consider making the bound lifetime-generic with a new `'a` lifetime | 2 | struct S2<F: for<'a> Fn(&'a i32, &'a i32) -> &'a i32>(F); | ^^^^^^^ ^^^^^^^ ^^^^^^^ ^^^ help: consider introducing a named lifetime parameter | 2 | struct S2<'a, F: Fn(&'a i32, &'a i32) -> &'a i32>(F);= | ^^^ ^^^^^^^ ^^^^^^^ ^^^ ``` Follow up to #68267. Addresses the diagnostics part of #49287.
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Taking inspiration from the narrative in @fasterthanlime's https://fasterthanli.me/blog/2019/declarative-memory-management/, add suggestions to some lifetime definition errors.