docs(rpc): document the promise chain inference limitation - #897
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yusukebe merged 2 commits intoAug 22, 2026
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A handler that returns a `.then()` chain directly infers `unknown` on the client. Inside the callback, the type of `c` depends on the handler's return type, which is what the callback is being used to infer, so TypeScript falls back to the constraint of the return type and the response type is lost. Document the limitation under "Known issues" together with the two ways around it, as suggested in honojs/hono#4765. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019bYuvGzZDDeCezDyTF1T5n
yusukebe
approved these changes
Aug 22, 2026
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Documents the RPC limitation reported in honojs/hono#4765, where a handler that
returns a
.then()chain directly infersunknownon the client.@yusukebe suggested
leaving the behaviour as-is and documenting the limitation, so this adds it
under "Known issues" in the RPC guide, with the reason it happens and the two
ways around it.
Each snippet was checked against
honomain:.then()chain infersunknownc.json(d)infers{ hello: string }then<TypedResponse<{ hello: string }, 200, 'json'>>infers{ hello: string }TypedResponseis used for the annotation becauseJSONRespondReturnis notexported from the package.