Implement fall-through errors.

lib/kernel_visitor.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.md file.
 
 library rasta.kernel_visitor;
 
 import 'package:kernel/ast.dart' as ir;
 
 import 'package:kernel/frontend/accessors.dart' show
     Accessor,
@@ skipping 158 matching lines @@
 import 'unresolved.dart' show
     RastaUnresolved;
 
 import 'error.dart' show
     RastaError;
 
 import 'kernel.dart' show
     ConstructorTarget,
     Kernel;
 
+import 'kernel/fall_through_visitor.dart' show
+    fallsThrough;
+
 /// Translates dart2js AST nodes [Node] into Kernel IR [ir.TreeNode].
 ///
 /// Most methods in this class have a prefix that follows these conventions:
 ///
 ///   * `visit` for overridden visitor methods.
 ///   * `handle` for methods that implement common behavior for several `visit`
 ///     methods. These methods are called by `visit` methods implemented by
 ///     various mixins below.
 ///   * `build` helper method that builds a new Kernel IR tree.
 ///   * `get` helper method that use a cache to build exactly one Kernel IR
@@ skipping 846 matching lines @@
         internalError(caseNode, "case node mismatch");
       }
       ir.SwitchCase irCase = casesIterator.current;
       List<ir.Statement> statements = <ir.Statement>[];
       bool hasVariableDeclaration = false;
       for (Statement statement in caseNode.statements.nodes) {
         if (buildStatement(statement, statements)) {
           hasVariableDeclaration = true;
         }
       }
+      if (statements.isEmpty || fallsThrough(statements.last)) {
+        statements.add(
+            new ir.ExpressionStatement(
+                new ir.Throw(
+                    new ir.StaticInvocation(
+                        kernel.getFallThroughErrorBuilder(),
+                        new ir.Arguments.empty()))));
+      }
       ir.Statement body;
       if (!hasVariableDeclaration && statements.length == 1) {
         body = statements.single;
       } else {
         body = new ir.Block(statements);
       }
       irCase.body = body;
       body.parent = irCase;
     }
     assert(!casesIterator.moveNext());
@@ skipping 1983 matching lines @@
       : this(null, true, node, initializers);
 
   accept(ir.Visitor v) => throw "unsupported";
 
   visitChildren(ir.Visitor v) => throw "unsupported";
 
   String toString() {
     return "IrFunction($kind, $isConstructor, $node, $initializers)";
   }
 }