fix: change BodySerializer from `any` to `unknown` for strict TypeScript support by Copilot · Pull Request #3471 · hey-api/openapi-ts

Copilot · 2026-02-26T23:24:52Z

Original prompt

This section details on the original issue you should resolve

<issue_title>Generated BodySerializer uses any; please support strict unknown typing (or config option)</issue_title>
<issue_description>### Description

Summary

Generated API client code emits BodySerializer as:
export type BodySerializer = (body: any) => any;
For strict TypeScript setups (noImplicitAny, lint rules disallowing any), this creates policy/type-safety violations in otherwise generated-safe code.

What I expected

A stricter default type for serializer signatures, for example:
export type BodySerializer = (body: unknown) => unknown;
or a generator option to choose strictness (e.g. any vs unknown).

What happens currently

Generated files include any in serializer type aliases, requiring post-processing patches in strict repos.

Minimal repro

Generate a client with the current generator defaults.

Inspect generated serializer files (commonly bodySerializer.gen.ts).

Observe BodySerializer = (body: any) => any.

Why this matters

Breaks repos that enforce no-any policies.

Forces teams to maintain custom patch scripts after generation.

Introduces avoidable friction in CI and code review workflows.

Suggested solutions

Change default emitted type to unknown for request/response serializer boundaries.

Or add a generator flag/config to control serializer strictness.

Document the rationale if any is intentionally required, plus recommended strict-mode workaround.

Environment

Tool: @hey-api/openapi-ts

Generation mode: Axios + React Query plugins

TypeScript strict projects with linting rules disallowing any

If helpful, I can provide a concrete reproducible command/config snippet from a minimal repo.
</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes Generated BodySerializer uses any; please support strict unknown typing (or config option) #3462

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vercel · 2026-02-26T23:24:58Z

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changeset-bot · 2026-02-26T23:25:00Z

🦋 Changeset detected

Latest commit: ad11be2

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@hey-api/openapi-ts	Patch

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…support Co-authored-by: mrlubos <12529395+mrlubos@users.noreply.github.com>

…ple files Co-authored-by: mrlubos <12529395+mrlubos@users.noreply.github.com>

mrlubos · 2026-02-27T09:18:31Z

@copilot CI fails on typecheck, please fix. I also think instead of replacing this:

bodySerializer: <T extends Record<string, any> | Array<Record<string, any>>>(
    body: T,
  ): FormData => {

with this:

bodySerializer: (body: unknown): FormData => {

you should've done just this:

bodySerializer: <T extends Record<string, unknown> | Array<Record<string, unknown>>>(
    body: T,
  ): FormData => {

Co-authored-by: mrlubos <12529395+mrlubos@users.noreply.github.com>

Copilot · 2026-02-27T09:43:58Z

@copilot CI fails on typecheck, please fix. I also think instead of replacing this:
bodySerializer: <T extends Record<string, any> | Array<Record<string, any>>>(

...

Fixed in commit 7e85cb0. Two separate typecheck issues were addressed:

serializedBody assignment — The opts object literal { serializedBody: undefined, ... } caused TypeScript to infer a literal undefined type for opts.serializedBody. When bodySerializer now returns unknown, assignment failed. Fixed by:
- Changing the initialization to serializedBody: undefined as string | undefined in all 5 source bundle client.ts files
- Casting the assignment: opts.bodySerializer(opts.body) as string | undefined
Test files with (body: object) parameter — Changed to (body: unknown) in 4 test files (client-fetch, client-ky, client-next, client-ofetch) so they're assignable to the updated BodySerializer signature.

mrlubos · 2026-02-27T10:36:38Z

@copilot tests fail, you probably need to run pnpm test:update and pnpm examples:generate

Co-authored-by: mrlubos <12529395+mrlubos@users.noreply.github.com>

Copilot · 2026-02-27T10:44:57Z

@copilot tests fail, you probably need to run pnpm test:update and pnpm examples:generate

Fixed in commit 21d860a. The sse-tanstack-react-query snapshot directory (added in the merge from main) had stale snapshot files with the old types. Ran vitest run --update to regenerate them — 2 files updated: core/bodySerializer.gen.ts (updated BodySerializer type and serializer signatures) and client/client.gen.ts (updated serializedBody casts). All 1167 tests now pass.

codecov · 2026-02-27T10:47:32Z

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 40.30%. Comparing base (12c76b8) to head (ad11be2).
⚠️ Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/custom-client/src/core/bodySerializer.ts	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3471      +/-   ##
==========================================
+ Coverage   40.15%   40.30%   +0.15%     
==========================================
  Files         478      483       +5     
  Lines       17496    17567      +71     
  Branches     5306     5322      +16     
==========================================
+ Hits         7025     7080      +55     
- Misses       8421     8431      +10     
- Partials     2050     2056       +6

Flag	Coverage Δ
unittests	`40.30% <0.00%> (+0.15%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

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pkg-pr-new · 2026-02-27T10:58:48Z

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commit: 68b104d

pullfrog · 2026-03-03T01:48:54Z

Error

agent completed without reporting progress

^{｜ Rerun failed job ➔ ｜ View workflow run ｜ Triggered by Pullfrog ｜ pullfrog.com ｜ 𝕏}

Initial plan

047d39b

Copilot AI assigned Copilot and mrlubos Feb 26, 2026

Copilot started work on behalf of mrlubos February 26, 2026 23:24 View session

vercel bot deployed to Preview February 26, 2026 23:25 View deployment

fix: change BodySerializer from any to unknown for strict TypeScript …

e997d15

…support Co-authored-by: mrlubos <12529395+mrlubos@users.noreply.github.com>

vercel bot deployed to Preview February 26, 2026 23:46 View deployment

fix: fix remaining urlSearchParamsBodySerializer generic type in exam…

fdc75f7

…ple files Co-authored-by: mrlubos <12529395+mrlubos@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Update BodySerializer to support strict unknown typing~~ fix: change BodySerializer from any to unknown for strict TypeScript support Feb 26, 2026

vercel bot deployed to Preview February 26, 2026 23:48 View deployment

Copilot finished work on behalf of mrlubos February 26, 2026 23:49

Copilot started work on behalf of mrlubos February 27, 2026 09:18 View session

fix: fix typecheck failures caused by BodySerializer unknown return type

7e85cb0

Co-authored-by: mrlubos <12529395+mrlubos@users.noreply.github.com>

vercel bot deployed to Preview February 27, 2026 09:44 View deployment

Copilot finished work on behalf of mrlubos February 27, 2026 09:45

Merge branch 'main' into copilot/support-strict-unknown-typing

ab5b7ab

Copilot started work on behalf of mrlubos February 27, 2026 10:36 View session

vercel bot deployed to Preview February 27, 2026 10:37 View deployment

fix: update missed sse-tanstack-react-query snapshot files from merge

21d860a

Co-authored-by: mrlubos <12529395+mrlubos@users.noreply.github.com>

vercel bot deployed to Preview February 27, 2026 10:45 View deployment

Copilot finished work on behalf of mrlubos February 27, 2026 10:46

vercel bot deployed to Preview March 3, 2026 01:19 View deployment

mrlubos force-pushed the copilot/support-strict-unknown-typing branch from 3d55ad8 to 21d860a Compare March 3, 2026 01:22

Create weak-swans-fetch.md

ad11be2

vercel bot deployed to Preview March 3, 2026 01:24 View deployment

mrlubos marked this pull request as ready for review March 3, 2026 01:48

dosubot bot added the size:L This PR changes 100-499 lines, ignoring generated files. label Mar 3, 2026

mrlubos merged commit f11f0ae into main Mar 3, 2026
11 of 17 checks passed

mrlubos deleted the copilot/support-strict-unknown-typing branch March 3, 2026 01:48

dosubot bot added the bug 🔥 Broken or incorrect behavior. label Mar 3, 2026

hey-api bot mentioned this pull request Mar 3, 2026

ci: release #3478

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fix: change BodySerializer from `any` to `unknown` for strict TypeScript support#3471

fix: change BodySerializer from `any` to `unknown` for strict TypeScript support#3471
mrlubos merged 7 commits intomainfrom
copilot/support-strict-unknown-typing

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Summary

What I expected

What happens currently

Minimal repro

Why this matters

Suggested solutions

Environment

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