fix: restore type safety on streaming chunk schema#21831
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peda-cos wants to merge 2 commits intoanomalyco:devfrom
Open
fix: restore type safety on streaming chunk schema#21831peda-cos wants to merge 2 commits intoanomalyco:devfrom
peda-cos wants to merge 2 commits intoanomalyco:devfrom
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## Problem
The streaming `transform` function in `OpenAICompatibleChatLanguageModel`
had lost type safety on the `Chunk` union type, caused by the error schema
being embedded directly inside the union alongside the base chunk shape.
This forced early binding of `chunk.value` before discriminating the error
branch, making TypeScript unable to narrow the type correctly downstream.
A TODO comment marked this as a known regression: "we lost type safety on
Chunk, most likely due to the error schema. MUST FIX".
## Root Cause
`createOpenAICompatibleChatChunkSchema` previously returned:
z.union([z.object({ ...fullShape... }), errorSchema])
The full base shape was inlined anonymously inside the union, making it
impossible to reference it as a standalone named type. As a result,
`chunk.value` could not be safely typed after the error branch was
discriminated away — TypeScript still saw it as the full union.
## Solution
Extract the base chunk object into a named top-level constant:
const chunkBaseSchema = z.object({ ... })
`createOpenAICompatibleChatChunkSchema` now composes it cleanly:
z.union([chunkBaseSchema, errorSchema])
In the `transform` function:
- Move `const value = chunk.value` *after* the error branch guard.
- Cast it explicitly as `z.infer<typeof chunkBaseSchema>` at the point of
assignment, which is now sound because the error branch has already
returned early.
- Access `chunk.value.error.message` directly inside the error branch,
before the cast, which is also correct since the union still carries the
error shape there.
## Changes
- `openai-compatible-chat-language-model.ts`
- Hoist `chunkBaseSchema` as a named module-level `const`.
- Simplify `createOpenAICompatibleChatChunkSchema` to
`z.union([chunkBaseSchema, errorSchema])`.
- Reorder `transform`: error guard first, then typed `value` assignment.
- Remove stale TODO comment.
## Impact
No runtime behavior change. Pure type-system fix: downstream code in
`transform` that consumes `value.choices`, `value.usage`, etc. is now
fully typed and will surface compile-time errors on schema drift.
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Thanks for updating your PR! It now meets our contributing guidelines. 👍 |
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Issue for this PR
Closes #21833
Type of change
What does this PR do?
There was a TODO in the Copilot chat streaming transform saying type safety was lost on the
Chunktype. The root cause is thatthis.chunkSchemais az.unionwhere the second arm is a generic error schema. TypeScript can't inferz.infer<typeof this.chunkSchema>correctly through that union, sochunk.valueends up untyped on the success path.The fix extracts the base chunk object schema into a module-level
const chunkBaseSchemainstead of having it inlined inside the class method. Then, after the two error guards (!chunk.successand"error" in chunk.value) have already narrowed the path, it castschunk.value as z.infer<typeof chunkBaseSchema>. This is the same pattern used in the upstreamvercel/airepo for the same problem.How did you verify your code works?
Ran
bun typecheckfrompackages/opencodeand got no errors. The TODO comment is gone and the success path now has a concrete type instead ofany.Screenshots / recordings
N/A, no UI changes.
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