Document proper usage of fmt::Error and fmt()'s Result.
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Documentation of these properties previously existed in a lone paragraph in the `fmt` module's documentation: <https://doc.rust-lang.org/1.78.0/std/fmt/index.html#formatting-traits> However, users looking to implement a formatting trait won't necessarily look there. Therefore, let's add the critical information (that formatting per se is infallible) to all the involved items.
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r? @Nilstrieb rustbot has assigned @Nilstrieb. Use |
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I wonder if this should be made into a panic then, since it can't be reached unless there's a bug in the formatter? |
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that should indeed be unreachable unless someone has a fallible formatting impl. not sure whether it's worth panicking in that case though, maybe. |
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We do panic in the equivalent case in |
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…iaskrgr Rollup of 5 pull requests Successful merges: - rust-lang#124928 (Stabilize `byte_slice_trim_ascii` for `&[u8]`/`&str`) - rust-lang#124954 (Document proper usage of `fmt::Error` and `fmt()`'s `Result`.) - rust-lang#124969 (check if `x test tests` missing any test directory) - rust-lang#124978 (Handle Deref expressions in invalid_reference_casting) - rust-lang#125005 (Miri subtree update) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#124954 - kpreid:fmterr, r=Nilstrieb Document proper usage of `fmt::Error` and `fmt()`'s `Result`. I've seen several newcomers wonder why `fmt::Error` doesn't have any error detail information, or propose to return it in response to an error condition found inside a `impl fmt::Display for MyType`. That is incorrect, per [a lone paragraph of the `fmt` module's documentation](https://doc.rust-lang.org/1.78.0/std/fmt/index.html#formatting-traits). However, users looking to implement a formatting trait won't necessarily look there. Therefore, let's add the critical information (that formatting per se is infallible) to all the involved items: every `fmt()` method, and `fmt::Error`. This PR is not intended to make any novel claims about `fmt`; only to repeat an existing one in places where it will be more visible.
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…crum,workingjubilee io::Write::write_fmt: panic if the formatter fails when the stream does not fail Follow-up to rust-lang#124954
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…ingjubilee io::Write::write_fmt: panic if the formatter fails when the stream does not fail Follow-up to rust-lang/rust#124954
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I've seen several newcomers wonder why
fmt::Errordoesn't have any error detail information, or propose to return it in response to an error condition found inside aimpl fmt::Display for MyType.That is incorrect, per a lone paragraph of the
fmtmodule's documentation. However, users looking to implement a formatting trait won't necessarily look there. Therefore, let's add the critical information (that formatting per se is infallible) to all the involved items: everyfmt()method, andfmt::Error.This PR is not intended to make any novel claims about
fmt; only to repeat an existing one in places where it will be more visible.