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

[LeCarbonator]

Closes #1614
Closes #1561
Closes #1577 , though it's not clear if it unintentionally broke something else solid-form-related.
Affects #1289 , though I have not confirmed that it fixes deleteField yet. Feedback from author is appreciated
Might close #1638 , feedback from author is needed

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 97a9877

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---

☁️ Nx Cloud last updated this comment at 2025-10-02 19:37:39 UTC

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commit: 97a9877

[codecov]

Codecov Report

❌ Patch coverage is 98.75000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.59%. Comparing base (6892ed0) to head (97a9877).
⚠️ Report is 23 commits behind head on main.

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

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1729      +/-   ##
==========================================
+ Coverage   90.35%   90.59%   +0.24%     
==========================================
  Files          38       38              
  Lines        1752     1787      +35     
  Branches      444      446       +2     
==========================================
+ Hits         1583     1619      +36     
  Misses        149      149              
+ 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]

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Latest commit: 97a9877

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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.