Merge pull request #2843 from Hixie/nan-constraints

Handle NaNs in constraints, just in case.

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

@@ -305,6 +305,29 @@ class BoxConstraints extends Constraints {
   @override
   bool get debugAssertIsNormalized {
     assert(() {
+      if (minWidth.isNaN || maxWidth.isNaN || minHeight.isNaN || maxHeight.isNaN) {
+        List<String> affectedFieldsList = <String>[];
+        if (minWidth.isNaN)
+          affectedFieldsList.add('minWidth');
+        if (maxWidth.isNaN)
+          affectedFieldsList.add('maxWidth');
+        if (minHeight.isNaN)
+          affectedFieldsList.add('minHeight');
+        if (maxHeight.isNaN)
+          affectedFieldsList.add('maxHeight');
+        assert(affectedFieldsList.length > 0);
+        if (affectedFieldsList.length > 1)
+          affectedFieldsList.add('and ${affectedFieldsList.removeLast()}');
+        String whichFields = '';
+        if (affectedFieldsList.length > 2) {
+          whichFields = affectedFieldsList.join(', ');
+        } else if (affectedFieldsList.length == 2) {
+          whichFields = affectedFieldsList.join(' ');
+        } else {
+          whichFields = affectedFieldsList.single;
+        }
+        throw new FlutterError('BoxConstraints has ${affectedFieldsList.length == 1 ? 'a NaN value' : 'NaN values' } in $whichFields.\n$this');
+      }
       if (minWidth < 0.0 && minHeight < 0.0)
         throw new FlutterError('BoxConstraints has both a negative minimum width and a negative minimum height.\n$this');
       if (minWidth < 0.0)

packages/flutter/test/rendering/constraints_test.dart

@@ -30,4 +30,44 @@ void main() {
     expect(leaf.size.width, equals(400.0));
     expect(leaf.size.height, equals(100.0));
   });
+
+  test("BoxConstraints with NaN", () {
+    String result;
+
+    result = 'no exception';
+    try {
+      BoxConstraints constraints = new BoxConstraints(minWidth: double.NAN, maxWidth: double.NAN, minHeight: 2.0, maxHeight: double.NAN);
+      assert(constraints.debugAssertIsNormalized);
+    } on FlutterError catch (e) {
+      result = '$e';
+    }
+    expect(result, equals(
+      'BoxConstraints has NaN values in minWidth, maxWidth, and maxHeight.\n'
+      'BoxConstraints(NaN<=w<=NaN, 2.0<=h<=NaN; NOT NORMALIZED)'
+    ));
+
+    result = 'no exception';
+    try {
+      BoxConstraints constraints = new BoxConstraints(minHeight: double.NAN);
+      assert(constraints.debugAssertIsNormalized);
+    } on FlutterError catch (e) {
+      result = '$e';
+    }
+    expect(result, equals(
+      'BoxConstraints has a NaN value in minHeight.\n'
+      'BoxConstraints(0.0<=w<=Infinity, NaN<=h<=Infinity; NOT NORMALIZED)'
+    ));
+
+    result = 'no exception';
+    try {
+      BoxConstraints constraints = new BoxConstraints(minHeight: double.NAN, maxWidth: 0.0/0.0);
+      assert(constraints.debugAssertIsNormalized);
+    } on FlutterError catch (e) {
+      result = '$e';
+    }
+    expect(result, equals(
+      'BoxConstraints has NaN values in maxWidth and minHeight.\n'
+      'BoxConstraints(0.0<=w<=NaN, NaN<=h<=Infinity; NOT NORMALIZED)'
+    ));
+  });
 }