Reland "ConstraintsTransformBox (#77994)" reverted in (#78661) (#78673)

packages/flutter/lib/src/rendering/debug_overflow_indicator.dart

@@ -85,7 +85,8 @@ class _OverflowRegionData {
 ///
 /// See also:
 ///
-///  * [RenderUnconstrainedBox] and [RenderFlex] for examples of classes that use this indicator mixin.
+///  * [RenderConstraintsTransformBox], [RenderUnconstrainedBox] and
+///    [RenderFlex], for examples of classes that use this indicator mixin.
 mixin DebugOverflowIndicatorMixin on RenderObject {
   static const Color _black = Color(0xBF000000);
   static const Color _yellow = Color(0xBFFFFF00);

packages/flutter/test/rendering/box_test.dart

@@ -378,6 +378,71 @@ void main() {
     expect(unconstrained.getMaxIntrinsicWidth(100.0), equals(200.0));
   });
 
+  group('ConstraintsTransfromBox', () {
+    FlutterErrorDetails? firstErrorDetails;
+    void exhaustErrors() {
+      FlutterErrorDetails? next;
+      do {
+        next = renderer.takeFlutterErrorDetails();
+        firstErrorDetails ??= next;
+      } while (next != null);
+    }
+
+    tearDown(() {
+      firstErrorDetails = null;
+      RenderObject.debugCheckingIntrinsics = false;
+    });
+
+    test('throws if the resulting constraints are not normalized', () {
+      final RenderConstrainedBox child = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(height: 0));
+      final RenderConstraintsTransformBox box = RenderConstraintsTransformBox(
+        alignment: Alignment.center,
+        textDirection: TextDirection.ltr,
+        constraintsTransform: (BoxConstraints constraints) => const BoxConstraints(maxHeight: -1, minHeight: 200),
+        child: child,
+      );
+
+      layout(box, constraints: const BoxConstraints(), onErrors: exhaustErrors);
+
+      expect(firstErrorDetails?.toString(), contains('is not normalized'));
+    });
+
+    test('overflow is reported when insufficient size is given', () {
+      final RenderConstrainedBox child = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: double.maxFinite));
+      final RenderConstraintsTransformBox box = RenderConstraintsTransformBox(
+        alignment: Alignment.center,
+        textDirection: TextDirection.ltr,
+        constraintsTransform: (BoxConstraints constraints) => constraints.copyWith(maxWidth: double.infinity),
+        child: child,
+      );
+
+      layout(box, constraints: const BoxConstraints(), phase: EnginePhase.composite, onErrors: expectOverflowedErrors);
+    });
+
+    test('handles flow layout', () {
+      final RenderParagraph child = RenderParagraph(
+        TextSpan(text: 'a' * 100),
+        textDirection: TextDirection.ltr,
+      );
+      final RenderConstraintsTransformBox box = RenderConstraintsTransformBox(
+        alignment: Alignment.center,
+        textDirection: TextDirection.ltr,
+        constraintsTransform: (BoxConstraints constraints) => constraints.copyWith(maxWidth: double.infinity),
+        child: child,
+      );
+
+      // With a width of 30, the RenderParagraph would have wrapped, but the
+      // RenderConstraintsTransformBox allows the paragraph to expand regardless
+      // of the width constraint:
+      // unconstrainedHeight * numberOfLines = constrainedHeight.
+      final double constrainedHeight = child.getMinIntrinsicHeight(30);
+      final double unconstrainedHeight = box.getMinIntrinsicHeight(30);
+
+      // At least 2 lines.
+      expect(constrainedHeight, greaterThanOrEqualTo(2 * unconstrainedHeight));
+    });
+  });
+
   test ('getMinIntrinsicWidth error handling', () {
     final RenderUnconstrainedBox unconstrained = RenderUnconstrainedBox(
       textDirection: TextDirection.ltr,

packages/flutter/test/rendering/debug_overflow_indicator_test.dart

@@ -36,7 +36,7 @@ void main() {
     final dynamic exception = tester.takeException();
     expect(exception, isFlutterError);
     expect(exception.diagnostics.first.level, DiagnosticLevel.summary);
-    expect(exception.diagnostics.first.toString(), startsWith('A RenderUnconstrainedBox overflowed by '));
+    expect(exception.diagnostics.first.toString(), startsWith('A RenderConstraintsTransformBox overflowed by '));
     expect(find.byType(UnconstrainedBox), paints..rect());
 
     await tester.pumpWidget(

packages/flutter/test/widgets/basic_test.dart

@@ -323,6 +323,7 @@ void main() {
       const UnconstrainedBox(constrainedAxis: Axis.vertical,).toString(),
       equals('UnconstrainedBox(alignment: Alignment.center, constrainedAxis: vertical)'),
     );
+
     expect(
       const UnconstrainedBox(constrainedAxis: Axis.horizontal, textDirection: TextDirection.rtl, alignment: Alignment.topRight).toString(),
       equals('UnconstrainedBox(alignment: Alignment.topRight, constrainedAxis: horizontal, textDirection: rtl)'),
@@ -331,13 +332,32 @@ void main() {
 
   testWidgets('UnconstrainedBox can set and update clipBehavior', (WidgetTester tester) async {
     await tester.pumpWidget(const UnconstrainedBox());
-    final RenderUnconstrainedBox renderObject = tester.allRenderObjects.whereType<RenderUnconstrainedBox>().first;
+    final RenderConstraintsTransformBox renderObject = tester.allRenderObjects.whereType<RenderConstraintsTransformBox>().first;
     expect(renderObject.clipBehavior, equals(Clip.none));
 
     await tester.pumpWidget(const UnconstrainedBox(clipBehavior: Clip.antiAlias));
     expect(renderObject.clipBehavior, equals(Clip.antiAlias));
   });
 
+  group('ConstraintsTransformBox', () {
+    test('toString', () {
+      expect(
+        const ConstraintsTransformBox(
+          constraintsTransform: ConstraintsTransformBox.unconstrained,
+        ).toString(),
+        equals('ConstraintsTransformBox(alignment: Alignment.center, constraints transform: unconstrained)'),
+      );
+      expect(
+        const ConstraintsTransformBox(
+          textDirection: TextDirection.rtl,
+          alignment: Alignment.topRight,
+          constraintsTransform: ConstraintsTransformBox.widthUnconstrained,
+        ).toString(),
+        equals('ConstraintsTransformBox(alignment: Alignment.topRight, textDirection: rtl, constraints transform: width constraints removed)'),
+      );
+    });
+  });
+
   group('ColoredBox', () {
     late _MockCanvas mockCanvas;
     late _MockPaintingContext mockContext;