InputDecorator negative baseline error message (#74837)

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

@@ -935,9 +935,20 @@ class _RenderDecoration extends RenderBox {
     // baseline from the alphabetic baseline. The ideographic baseline is for
     // use post-layout and is derived from the alphabetic baseline combined with
     // the font metrics.
-    final double? baseline = box.getDistanceToBaseline(TextBaseline.alphabetic);
-    assert(baseline != null && baseline >= 0.0);
-    return baseline!;
+    final double baseline = box.getDistanceToBaseline(TextBaseline.alphabetic)!;
+
+    assert(() {
+      if (baseline >= 0)
+        return true;
+      throw FlutterError.fromParts(<DiagnosticsNode>[
+        ErrorSummary("One of InputDecorator's children reported a negative baseline offset."),
+        ErrorDescription(
+          '${box.runtimeType}, of size ${box.size}, reported a negative '
+          'alphabetic baseline of $baseline.',
+        ),
+      ]);
+    }());
+    return baseline;
   }
 
   // Returns a value used by performLayout to position all of the renderers.
@@ -1767,7 +1778,9 @@ class _AffixText extends StatelessWidget {
 /// [InputDecorator] can be used to create widgets that look and behave like a
 /// [TextField] but support other kinds of input.
 ///
-/// Requires one of its ancestors to be a [Material] widget.
+/// Requires one of its ancestors to be a [Material] widget. The [child] widget,
+/// as well as the decorative widgets specified in [decoration], must have
+/// non-negative baselines.
 ///
 /// See also:
 ///

packages/flutter/test/material/input_decorator_test.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -4420,4 +4421,42 @@ void main() {
     final double intrinsicHeight = tester.getSize(find.byKey(intrinsicHeightKey)).height;
     expect(intrinsicHeight, equals(height));
   });
+
+  testWidgets('error message for negative baseline', (WidgetTester tester) async {
+    FlutterErrorDetails? errorDetails;
+    final FlutterExceptionHandler? oldHandler = FlutterError.onError;
+    FlutterError.onError = (FlutterErrorDetails details) {
+      errorDetails ??= details;
+    };
+    try {
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Center(
+            child: Directionality(
+              textDirection: TextDirection.ltr,
+              child: InputDecorator(
+                decoration: const InputDecoration(),
+                child: Stack(
+                  children: const <Widget>[
+                    SizedBox(height: 0),
+                    Positioned(
+                      bottom: 5,
+                      child: Text('ok'),
+                    ),
+                  ],
+                ),
+              ),
+            ),
+          ),
+        ),
+        null,
+        EnginePhase.layout,
+      );
+    } finally {
+      FlutterError.onError = oldHandler;
+    }
+
+    expect(errorDetails?.toString(), contains("InputDecorator's children reported a negative baseline"));
+    expect(errorDetails?.toString(), contains('RenderStack'));
+  });
 }