If RenderUnconstrainedBox.constrainedAxis was previously set, replace respectively:

Where constrainedAxis was previously Axis.horizontal, set
constraintsTransform to ConstraintsTransformBox.widthUnconstrained

Where constrainedAxis was previously Axis.vertical, set
constraintsTransform to ConstraintsTransformBox.heightUnconstrained

This change allowed for the introduction of several more types of constraint
transformations through ConstraintsTransformBox. Other parameters of the old
API are compatible with the new API.

Migration guide

Code before migration:

// Unconstrained

final

RenderUnconstrainedBox

unconstrained

RenderUnconstrainedBox

textDirection:

TextDirection

ltr

child:

RenderConstrainedBox

additionalConstraints:

const

BoxConstraints

tightFor