Unbounded TextField width error (#30796)

Improve the error message shown when a TextField ends up with an unbounded width.

packages/flutter/lib/src/material/input_decorator.dart

@@ -834,6 +834,17 @@ class _RenderDecoration extends RenderBox {
   // This method applies layout to all of the renderers except the container.
   // For convenience, the container is laid out in performLayout().
   _RenderDecorationLayout _layout(BoxConstraints layoutConstraints) {
+    assert(
+      layoutConstraints.maxWidth < double.infinity,
+      'An InputDecorator, which is typically created by a TextField, cannot '
+      'have an unbounded width.\n'
+      'This happens when the parent widget does not provide a finite width '
+      'constraint. For example, if the InputDecorator is contained by a Row, '
+      'then its width must be constrained. An Expanded widget or a SizedBox '
+      'can be used to constrain the width of the InputDecorator or the '
+      'TextField that contains it.',
+    );
+
     // Margin on each side of subtext (counter and helperError)
     final Map<RenderBox, double> boxToBaseline = <RenderBox, double>{};
     final BoxConstraints boxConstraints = layoutConstraints.loosen();