fix(form-core): fix fields being stale on array changes

[LeCarbonator]

Closes #1614
Closes #1561
Closes #1577
Closes #1289

Fixes:

• field.handleChange(undefined) no longer sets the value to the default value
• form.reset() and array methods no longer break controlled input when non-index keys are used
• field values in arrays no longer temporarily become undefined (breaking controlled -> uncontrolled -> controlled)

Todos:

• Test at workplace (known location where previous implementation crashed due to dnd)
• Test performance (what does the rerendering look like now?)
  • children callback
  • Form Composition
• Check other frameworks
  • Solid
  • Angular
  • Vue
  • Svelte
  • Lit

[nx-cloud]

View your CI Pipeline Execution ↗ for commit 91ced86

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nx run-many --target=build --exclude=examples/**	✅ Succeeded	1s	View ↗

---

☁️ Nx Cloud last updated this comment at 2025-10-30 09:31:39 UTC

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commit: 91ced86

[codecov]

Codecov Report

❌ Patch coverage is 97.53086% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.61%. Comparing base (6892ed0) to head (91ced86).
⚠️ Report is 43 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/form-core/src/FieldApi.ts	94.73%	1 Missing ⚠️
packages/form-core/src/metaHelper.ts	98.21%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1729      +/-   ##
==========================================
+ Coverage   90.35%   90.61%   +0.26%     
==========================================
  Files          38       38              
  Lines        1752     1812      +60     
  Branches      444      466      +22     
==========================================
+ Hits         1583     1642      +59     
- Misses        149      151       +2     
+ Partials       20       19       -1     

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[LeCarbonator]

Notes to self:

Swapping, deletion and basic reset seems to work. However, there's conflicts with the reset that need further investigating.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 91ced86

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[LeCarbonator]

form.reset() still has the issue if the array field's size changes.

swapValues, moveValues and removeValue seem to be fixed.

[LeCarbonator]

form.reset() and array methods are all fixed.

Todos:

• Test at workplace (known location where previous implementation crashed due to dnd)
• Test performance (what does the rerendering look like now?)
  • children callback
  • Form Composition
• Check other frameworks
  • Solid
  • Angular
  • Vue
  • Svelte
  • Lit

[LeCarbonator]

Solid appears to be struggling with this implementation still. I'll look into what can be done to fix it.

[LeCarbonator]

Looks like svelte has a problem when using a keyed list

[LeCarbonator]

Arrays look to be fixed, at least confirmed for React.

However, it looks like defaultValue and defaultMeta have been broken in the process. This might also highlight stale unit tests, so I'll have to go through that thoroughly.