fix(typescript): apply exactOptionalPropertyTypes to inline request types

[Swimburger]

Description

Supersedes / completes #16972 (whose branch lives on a fork I can't push to). Includes the original commit plus the follow-ups needed to make the change land consistently.

With noSerdeLayer: true, optional properties on inline request types (client/requests/*) are now generated as propName?: Type | undefined, matching what the object type generator already does for type declarations. This satisfies exactOptionalPropertyTypes: true so callers can explicitly set optional fields to undefined.

Changes Made

• Request wrapper widening (GeneratedRequestWrapperImpl.ts): when a property is optional and the serde layer is off, widen its type node to T | undefined (same !includeSerdeLayer gate the object generator uses). (original fix(typescript): apply exactOptionalPropertyTypes to inline request types #16972 change)
• Fix double-undefined on optional file uploads (Devin Review finding on fix(typescript): apply exactOptionalPropertyTypes to inline request types #16972): getFileParameterType already appends | undefined for optional files, so the naive widening produced Uploadable | undefined | undefined. Now strip any top-level undefined before re-adding it.
• Shared stripTopLevelUndefined util: extracted the strip logic (previously private methods in GeneratedObjectTypeImpl) into @fern-typescript/commons/codegen-utils/stripTopLevelUndefined.ts, and refactored both the object type generator and request wrapper generator to use it — so both emission paths handle widening identically.
• Changelog: moved the hand-edited versions.yml entry into generators/typescript/sdk/changes/unreleased/apply-exact-optional-to-request-types.yml (type: fix); versions.yml reverted to match main (versioning is automation-driven).
• Regenerated ts-sdk seed outputs to capture the new widening. Example, file-upload/.../OptionalArgsRequest.ts:

  export interface OptionalArgsRequest {
      image_file?: core.file.Uploadable | undefined;   // stays single — no double undefined
  -   request?: unknown;
  +   request?: unknown | undefined;
  }

Testing

• pnpm turbo run compile --filter @fern-typescript/* — passes
• biome check on all changed generator sources — passes
• pnpm seed test --generator ts-sdk --local --skip-scripts — 225/225 fixtures pass
• Unit tests added/updated — none added (change exercised via seed fixtures)

Link to Devin session: https://app.devin.ai/sessions/a0d61f68646b4af789c322fda6cb4fc4
Requested by: @Swimburger

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[devin-ai-integration]

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[nitpickybot]

The PR extracts the top-level-undefined-stripping helper into a shared util and applies the exactOptionalPropertyTypes widening to inline request types when the serde layer is off. The core generator change is small, correctly gated, and handles the double-undefined file upload case. The regenerated seed outputs are consistent with the change. No blocking issues found.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

[github-actions]

SDK Generation Benchmark Results

Comparing PR branch against median of 5 nightly run(s) on main (latest: 2026-07-08T05:02:29Z).

Full benchmark table (click to expand)

Generator	Spec	main (generator)	main (E2E)	PR (generator)	Delta
ts-sdk	square	129s (n=5)	129s (n=5)	117s	-12s (-9.3%)

main (generator): generator-only time via --skip-scripts (includes Docker image build, container startup, IR parsing, and code generation — this is the same Docker-based flow customers use via fern generate). main (E2E): full customer-observable time including build/test scripts (nightly baseline, informational). Delta is computed against generator-only baseline.
⚠️ = generation exited with a non-zero exit code (timing may not reflect a successful run).
Baseline from nightly runs on main (latest: 2026-07-08T05:02:29Z). Trigger benchmark-baseline to refresh.
Last updated: 2026-07-08 21:59 UTC