Make LUB algorithm aware of non-null types

pkg/analyzer/test/src/task/strong/non_null_checker_test.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // These tests are for an experimental feature that treats Dart primitive types
 // (int, bool, double, etc.) as non-nullable. This file is not evidence for an
 // intention to officially support non-nullable primitives in Dart (or general
 // NNBD, for that matter) so don't get too crazy about it.
 
 library analyzer.test.src.task.non_null_primitives.checker_test;
@@ skipping 30 matching lines @@
   }
 }
 ''');
   }
 
   void test_nullableTypes() {
     // By default x can be set to null.
     checkFile('int x = null;');
   }
 
-  void test_nonnullableTypes() {
+  void test_uninitialized_nonnullable() {
     // If `int`s are non-nullable, then this code should throw an error.
     addFile('int x;');
+    check(nonnullableTypes: <String>['dart:core,int']);
+  }
+
+  void test_initialize_nonnullable_with_null() {
     addFile('int x = /*error:INVALID_ASSIGNMENT*/null;');
+    check(nonnullableTypes: <String>['dart:core,int']);
+  }
+
+  void test_initialize_nonnullable_with_valid_value() {
     addFile('int x = 0;');
+    check(nonnullableTypes: <String>['dart:core,int']);
+  }
+
+  void test_assign_null_to_nonnullable() {
     addFile('''
 int x = 0;
 
 main() {
   x = 1;
   x = /*error:INVALID_ASSIGNMENT*/null;
 }
 ''');
     check(nonnullableTypes: <String>['dart:core,int']);
   }
+
+  // Default example from NNBD document.
+  final String defaultNnbdExample = '''
+class Point {
+  final int x, y;
+  Point(this.x, this.y);
+  Point operator +(Point other) => new Point(x + other.x, y + other.y);
+  String toString() => "x: \$x, y: \$y";
 }
+
+void main() {
+  Point p1 = new Point(0, 0);
+  Point p2 = new Point(10, 10);
+  print("p1 + p2 = \${p1 + p2}");
+}
+''';
+
+  final String defaultNnbdExampleMod1 = '''
+class Point {
+  final int x, y;
+  Point(this.x, this.y);
+  Point operator +(Point other) => new Point(x + other.x, y + other.y);
+  String toString() => "x: \$x, y: \$y";
+}
+
+void main() {
+  Point p1 = new Point(0, 0);
+  Point p2 = new Point(10, /*boom*/null); // Change here.
+  print("p1 + p2 = \${p1 + p2}");
+}
+''';
+
+  final String defaultNnbdExampleMod2 = '''
+class Point {
+  final int x, y;
+  Point(this.x, this.y);
+  Point operator +(Point other) => new Point(x + other.x, y + other.y);
+  String toString() => "x: \$x, y: \$y";
+}
+
+void main() {
+  bool f = false; // Necessary, because dead code is otherwise detected.
+  Point p1 = new Point(0, 0);
+  Point p2 = new Point(10, /*boom*/f ? 10 : null); // Change here.
+  print("p1 + p2 = \${p1 + p2}");
+}
+''';
+
+  void test_nullable_fields() {
+    addFile(defaultNnbdExample);
+    // `null` can be passed as an argument to `Point` in default mode.
+    addFile(defaultNnbdExampleMod1);
+    // A nullable expression can be passed as an argument to `Point` in default
+    // mode.
+    addFile(defaultNnbdExampleMod2);
+    check();
+  }
+
+  void test_nonnullable_fields() {
+    addFile(defaultNnbdExample);
+    // `null` can be passed as an argument to `Point` in default mode.
+    addFile(_withError(defaultNnbdExampleMod1, "error:INVALID_ASSIGNMENT"));
+    // A nullable expression can be passed as an argument to `Point` in default
+    // mode.
+    addFile(_withError(defaultNnbdExampleMod2, "error:INVALID_ASSIGNMENT"));
+    check(nonnullableTypes: <String>['dart:core,int']);
+  }
+}
+
+String _withError(String file, String error) {
+  return ("" + file).replaceFirst("boom", error);
+}