Disallow uninitialized non-nullable variables

pkg/analyzer/lib/src/task/strong/checker.dart

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this was ported from package:dev_compiler, and needs to be
 // refactored to fit into analyzer.
 library analyzer.src.task.strong.checker;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 611 matching lines @@
         var initializer = variable.initializer;
         if (initializer != null) {
           checkAssignment(initializer, type.type);
         }
       }
     }
     node.visitChildren(this);
   }
 
   @override
+  Object visitVariableDeclaration(VariableDeclaration node) {
+    if (!node.isConst &&
+        !node.isFinal &&
+        node.initializer == null &&
+        rules.isNonNullableType(node?.element?.type)) {
+      _recordMessage(
+          node,
+          StaticTypeWarningCode.NON_NULLABLE_FIELD_NOT_INITIALIZED,
+          [node.name, node?.element?.type]);
+    }
+    return super.visitVariableDeclaration(node);
+  }
+
+  @override
   void visitWhileStatement(WhileStatement node) {
     checkBoolean(node.condition);
     node.visitChildren(this);
   }
 
   @override
   void visitYieldStatement(YieldStatement node) {
     _checkReturnOrYield(node.expression, node, yieldStar: node.star != null);
     node.visitChildren(this);
   }
@@ skipping 847 matching lines @@
     var visited = new Set<InterfaceType>();
     do {
       visited.add(current);
       current.mixins.reversed.forEach(
           (m) => _checkIndividualOverridesFromClass(node, m, seen, true));
       _checkIndividualOverridesFromClass(node, current.superclass, seen, true);
       current = current.superclass;
     } while (!current.isObject && !visited.contains(current));
   }
 }