Fix: Date/BigInt transformers not returning transformed values in array map callbacks

[Copilot]

Date and BigInt transformers were generating expressions that created transformed objects but failed to return them in array map callbacks, causing runtime type mismatches where TypeScript claimed Date but runtime had string.

Changes

• expressions.ts: Wrap dateExpressions and bigIntExpressions in return statements when dataExpression is a string (array item context)

Before/After

// Before - creates Date but doesn't return it
data = data.map((item: any) => {
    new Date(item);
    return item;  // returns original string
});

// After - returns transformed value
data = data.map((item: any) => {
    return new Date(item);
});

Test Coverage

Added transformers-array-date-ref.json spec covering:

• Arrays of primitive dates (array<string format=date-time>)
• Collection schemas via $ref to array types
• SDK integration with responseTransformer option

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Date transformers not generated for collection endpoints using $ref</issue_title>
<issue_description>### Description

Description

Date transformers are not generated for collection endpoints, when:

1. Collection items use $ref to reference component schemas (not inline schemas)
2. The same schema component IS transformed correctly when used directly

Expected Behavior

The same schema component (UserMatch.jsonld-match.collection.read) IS transformed correctly when used directly:

• Single-item endpoint (/api/admin/{company}/matches/{id}/{kind}) → transformer generated
• Collection endpoint (/api/admin/{company}/matches) → transformer NOT generated

Generated code:

export function getAdminCompanyMatchesIdKind(...) {
  return client.get({
    responseTransformer: apiAdminCompanymatchesIdKindGetResponseTransformer,
    url: '/api/admin/{company}/matches/{id}/{kind}',
  })
}

export function listAdminCompanyMatches(...) {
  return client.get({
    // responseTransformer: MISSING
    url: '/api/admin/{company}/matches',
  })
}

Actual Behavior

1. TypeScript types claim dates are Date: lastMessageSentAt?: Date | null
2. Runtime data has dates as strings (JSON doesn't have Date types)
3. Code expecting Date objects fails at runtime (e.g., calling .getTime() on a string)

Reproducible example or configuration

https://stackblitz.com/edit/hey-api-client-fetch-example-a95akxjr?file=repro-client%2Fsdk.gen.ts

OpenAPI specification (optional)

No response

System information (optional)

No response</issue_description>

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

• Fixes Date transformers not generated for collection endpoints using $ref #2902

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Project	Deployment	Preview	Comments	Updated (UTC)
hey-api-docs	Ready	Preview	Comment	Oct 31, 2025 4:00pm

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 30.89%. Comparing base (6d2622f) to head (691b212).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/src/plugins/@hey-api/transformers/expressions.ts	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2906      +/-   ##
==========================================
- Coverage   30.89%   30.89%   -0.01%     
==========================================
  Files         488      488              
  Lines       40458    40464       +6     
  Branches     2522     2523       +1     
==========================================
  Hits        12501    12501              
- Misses      27922    27928       +6     
  Partials       35       35              

Flag	Coverage Δ
unittests	30.89% <0.00%> (-0.01%)	⬇️

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