feat: add #[diagnostic::on_unimplemented] to IntoResponse and IntoResponseParts#3723
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yanns merged 3 commits intotokio-rs:mainfrom Apr 15, 2026
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…ponseParts Add #[diagnostic::on_unimplemented] attributes to the IntoResponse and IntoResponseParts traits, matching the pattern already used on FromRequest, FromRequestParts, and Handler. This improves compiler error messages when users forget to implement these traits on their response types, providing a direct link to the relevant documentation.
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Apr 14, 2026
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Motivation
The
FromRequest,FromRequestParts, andHandlertraits already use#[diagnostic::on_unimplemented]to provide helpful compiler messages when users encounter trait bound errors. However,IntoResponseandIntoResponseParts— two of the most commonly encountered traits in error messages — lack this attribute.When users forget to implement
IntoResponseon their custom response types (or return types that don't implement it), the compiler shows a bare "trait bound not satisfied" error without guidance.Solution
Add
#[diagnostic::on_unimplemented]to bothIntoResponseandIntoResponsePartstraits inaxum-core, with links to the relevant documentation pages. This matches the existing pattern used by the extractor and handler traits.