Improvements around custom error handling in ServerFnError #3253
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Contrary to an empty struct, which has exactly 1 possible value, an empty enum has 0 possible values: it can't even be constructed. Fixes leptos-rs#3154
This adds 3 new traits: - `ConvertServerFnResult` provides easy conversion from `Result<T, ServerFnError<SourceCustErr>>` to `Result<T, ServerFnError<TargetCustError>>` when `TargetCustError` implements `From<SourceCustErr>` - `ConvertDefaultServerFnResult` provides easy conversion from `Result<T, ServerFnError<NoCustomError>` to `Result<T, ServerFnError<TargetCustError>>` - `IntoServerFnResult` provides easy conversion from `Result<T, E>` to `Result<T, ServerFnError::ServerError>` when `E` implements `std::error::Error` Fixes leptos-rs#3153 and leptos-rs#3155
nicolas-guichard
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I think there are some nice utilities here. Originally I had meant the server_fn_error! macro to convert Error into ServerFnError depending on the traits Error implemented. I suspect that can be expanded to handle some of these conversions here and land on a more general single trait. |
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What's the target MSRV? The CI apparently uses an old Rust nightly 2024-08-01, and the build fails because omitting empty types in pattern matching is a Rust 1.82 feature. |
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We don't have an official MSRV policy but if it's simply a matter of adding a missing branch in a match, then yes you should add it. |
| type Err = (); | ||
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| fn from_str(_s: &str) -> Result<Self, Self::Err> { | ||
| Ok(NoCustomError) | ||
| fn from_str(_: &str) -> Result<Self, Self::Err> { | ||
| Err(()) |
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Ironically, I do think Infallible would make sense here as the Err type for FromStr (since it implements Error), but this is a breaking change so not sure if its worth the effort.
This implements a fix for #3154 by making
NoDefaultErrorunhinabited, and proposes workarounds for #3153 and #3155 to make converting easier:Result<T, ServerFnError<NoCustomError>>toResult<T, ServerFnError<AnyOtherCustomError>>Result<T, ServerFnError<SourceCustomError>>toResult<T, ServerFnError<TargetCustomError>>whenTargetCustomError: From<SourceCustomError>Result<T, E>toResult<T, ServerFnError<AnyCustomError>>whenE: std::error::Error, reflecting the existingFrom<E: std::error::Error> for ServerFnError<NoCustomError>Usage examples are provided in the docstring for each of these new traits. My typical uses cases are:
use_context.As mentioned in #3153 and #3155 I would have preferred implementing
From<ServerFnError<SourceCustomError>> for ServerFnError<TargetCustomError>andFrom<E: std::error::Error> for ServerFnError, but as @benwis correctly pointed out those conflict withFrom<T> for T, at least until specialization becomes available.