Adds FlexJustifyContent.collapse

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

@@ -46,6 +46,8 @@ enum FlexJustifyContent {
   spaceBetween,
   /// Place the free space evenly between the children as well as before and after the first and last child
   spaceAround,
+  /// Do not expand to fill the free space. None of the children may specify a flex factor.
+  collapse,
 }
 
 /// How the children should be placed along the cross axis in a flex layout
@@ -337,7 +339,7 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
     int totalChildren = 0;
     assert(constraints != null);
     final double mainSize = (_direction == FlexDirection.horizontal) ? constraints.constrainWidth() : constraints.constrainHeight();
-    final bool canFlex = mainSize < double.INFINITY;
+    final bool canFlex = mainSize < double.INFINITY && justifyContent != FlexJustifyContent.collapse;
     double crossSize = 0.0;  // This is determined as we lay out the children
     double freeSpace = canFlex ? mainSize : 0.0;
     RenderBox child = firstChild;
@@ -478,6 +480,7 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
     }
     switch (_justifyContent) {
       case FlexJustifyContent.start:
+      case FlexJustifyContent.collapse:
         leadingSpace = 0.0;
         betweenSpace = 0.0;
         break;

packages/unit/test/widget/flex_test.dart

@@ -42,4 +42,66 @@ void main() {
       expect(didReceiveTap, isTrue);
     });
   });
+
+  test('Row, Column and FlexJustifyContent.collapse', () {
+    final Key flexKey = new Key('flexKey');
+
+    // Row without justifyContent: FlexJustifyContent.collapse
+    testWidgets((WidgetTester tester) {
+      tester.pumpWidget(new Center(
+        child: new Row([
+          new Container(width: 10.0, height: 100.0),
+          new Container(width: 30.0, height: 100.0)
+        ],
+          key: flexKey
+        )
+      ));
+      Size flexSize = tester.findElementByKey(flexKey).renderObject.size;
+      expect(flexSize.width, equals(800.0));
+      expect(flexSize.height, equals(100.0));
+
+      // Row with justifyContent: FlexJustifyContent.collapse
+      tester.pumpWidget(new Center(
+        child: new Row([
+          new Container(width: 10.0, height: 100.0),
+          new Container(width: 30.0, height: 100.0)
+        ],
+          key: flexKey,
+          justifyContent: FlexJustifyContent.collapse
+        )
+      ));
+      flexSize = tester.findElementByKey(flexKey).renderObject.size;
+      expect(flexSize.width, equals(40.0));
+      expect(flexSize.height, equals(100.0));
+    });
+
+    // Column without justifyContent: FlexJustifyContent.collapse
+    testWidgets((WidgetTester tester) {
+      tester.pumpWidget(new Center(
+        child: new Column([
+          new Container(width: 100.0, height: 100.0),
+          new Container(width: 100.0, height: 150.0)
+        ],
+          key: flexKey
+        )
+      ));
+      Size flexSize = tester.findElementByKey(flexKey).renderObject.size;
+      expect(flexSize.width, equals(100.0));
+      expect(flexSize.height, equals(600.0));
+
+      // Column with justifyContent: FlexJustifyContent.collapse
+      tester.pumpWidget(new Center(
+        child: new Column([
+          new Container(width: 100.0, height: 100.0),
+          new Container(width: 100.0, height: 150.0)
+        ],
+          key: flexKey,
+          justifyContent: FlexJustifyContent.collapse
+        )
+      ));
+      flexSize = tester.findElementByKey(flexKey).renderObject.size;
+      expect(flexSize.width, equals(100.0));
+      expect(flexSize.height, equals(250.0));
+    });
+  });
 }