Fixed: Dimensions Custom Unit behaviour is not working as expected

[Mayank-Tripathi32]

fixes #68734

What?

The issue occurs when changing the typography dimensions (e.g., padding/margin) from "Use size preset" to "Set Custom Size" and switching the unit type from px to another unit. The selected unit resets back to px, requiring users to select their desired unit twice.

Why?

• Reset Behavior: The code resets the value due to improper handling of the selected unit and the fallback logic in the getValidParsedQuantityAndUnit function.
• Unit Validation: The nextValue computation doesn't persist the new unit properly, resulting in an override to the default (px).
• User Experience Issue: This creates unnecessary friction, as users need to repeat actions to achieve the intended result.

How?

The fix ensures the selected unit is preserved during the transition by improving the logic inside the getValidParsedQuantityAndUnit function:

• Introduced validation to check the current and next units.
• Applied fallback logic only when needed (e.g., reset defaults only if explicitly required).

Testing Instructions

1. Select any block paragraph, pullquote, quote, etc.
2. Add dummy text
3. Go to block settings and change "Typography Dimensions" from "Use size preset" to "Set Custom Size"
4. Now, change its type from "px" to any other based on requirement
5. Now, change size using range control.

Screencast

Screen.Recording.2025-01-17.at.4.24.55.PM.mov

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[stokesman]

While I haven’t tested this, I trust it fixes the issue yet I doubt that changing code in UnitControl is the best approach. That’s because I’ve tested another component BoxControl that also pairs UnitControl with a range input and it doesn’t have the same issue.

Here’s a quick demo trying to reproduce the issue in the BoxControl story:

box-control-empty-non-px-unit-and-range-drag.mp4

That leads me to think the issue is somewhere in SpacingSizesControl. Would you agree?