Added assert to prevent complete ListTile trailing/leading horizontal expansion (#30212)

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

@@ -165,12 +165,15 @@ enum ListTileControlAffinity {
 /// wraps to two lines (if it is true).
 ///
 /// The heights of the [leading] and [trailing] widgets are constrained
-/// according to the [Material spec]
-/// (https://material.io/design/components/lists.html).
+/// according to the
+/// [Material spec](https://material.io/design/components/lists.html).
 /// An exception is made for one-line ListTiles for accessibility. Please
 /// see the example below to see how to adhere to both Material spec and
 /// accessibility requirements.
 ///
+/// Note that [leading] and [trailing] widgets can expand as far as they wish
+/// horizontally, so ensure that they are properly constrained.
+///
 /// List tiles are typically used in [ListView]s, or arranged in [Column]s in
 /// [Drawer]s and [Card]s.
 ///
@@ -218,13 +221,13 @@ enum ListTileControlAffinity {
 /// that are large enough, but it is up to the developer to ensure that
 /// their widgets follow the Material spec.
 ///
-/// The following is an example of a one-line, non-[dense] ListTile with a
+/// {@tool sample}
+///
+/// Here is an example of a one-line, non-[dense] ListTile with a
 /// tappable leading widget that adheres to accessibility requirements and
 /// the Material spec. To adjust the use case below for a one-line, [dense]
 /// ListTile, adjust the vertical padding to 8.0.
 ///
-/// {@tool sample}
-///
 /// ```dart
 /// ListTile(
 ///   leading: GestureDetector(
@@ -984,6 +987,14 @@ class _RenderListTile extends RenderBox {
     final double tileWidth = looseConstraints.maxWidth;
     final Size leadingSize = _layoutBox(leading, iconConstraints);
     final Size trailingSize = _layoutBox(trailing, iconConstraints);
+    assert(
+      tileWidth != leadingSize.width,
+      'Leading widget consumes entire tile width. Please use a sized widget.'
+    );
+    assert(
+      tileWidth != trailingSize.width,
+      'Trailing widget consumes entire tile width. Please use a sized widget.'
+    );
 
     final double titleStart = hasLeading
       ? math.max(_minLeadingWidth, leadingSize.width) + _horizontalTitleGap