Avoid generating duplicate stubs. Fixes issue 3184.

lib/compiler/implementation/js_backend/emitter.dart

 // Copyright (c) 2012, 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.
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
 class ClosureInvocationElement extends FunctionElement {
   ClosureInvocationElement(SourceString name,
@@ skipping 333 matching lines @@
   /**
    * Generate stubs to handle invocation of methods with optional
    * arguments.
    *
    * A method like [: foo([x]) :] may be invoked by the following
    * calls: [: foo(), foo(1), foo(x: 1) :]. See the sources of this
    * function for detailed examples.
    */
   void addParameterStub(FunctionElement member,
                         Selector selector,
-                        DefineMemberFunction defineInstanceMember) {
+                        DefineMemberFunction defineInstanceMember,
+                        Set<String> alreadyGenerated) {
     FunctionSignature parameters = member.computeSignature(compiler);
     int positionalArgumentCount = selector.positionalArgumentCount;
     if (positionalArgumentCount == parameters.parameterCount) {
       assert(selector.namedArgumentCount == 0);
       return;
     }
     if (parameters.optionalParametersAreNamed
         && selector.namedArgumentCount == parameters.optionalParameterCount) {
       // If the selector has the same number of named arguments as
       // the element, we don't need to add a stub. The call site will
       // hit the method directly.
       return;
     }
     ConstantHandler handler = compiler.constantHandler;
     List<SourceString> names = selector.getOrderedNamedArguments();
 
     String invocationName =
         namer.instanceMethodInvocationName(member.getLibrary(), member.name,
                                            selector);
+    if (alreadyGenerated.contains(invocationName)) return;
+    alreadyGenerated.add(invocationName);
     CodeBuffer buffer = new CodeBuffer();
     buffer.add('function(');
 
     // The parameters that this stub takes.
     List<String> parametersBuffer = new List<String>(selector.argumentCount);
     // The arguments that will be passed to the real method.
     List<String> argumentsBuffer = new List<String>(parameters.parameterCount);
 
     int count = 0;
     int indexOfLastOptionalArgumentInParameters = positionalArgumentCount - 1;
@@ skipping 83 matching lines @@
     // (3) foo$3(a, b, c) => foo$4(a, b, c, null)
     // (4) foo$3$c(a, b, c) => foo$4(a, b, c, null);
     // (5) foo$3$d(a, b, d) => foo$4(a, b, null, d);
     // (6) foo$4$c$d(a, b, c, d) => foo$4(a, b, c, d);
     // (7) Same as (5).
     //
     // We need to generate a stub for (5) because the order of the
     // stub arguments and the real method may be different.
     Set<Selector> selectors = compiler.codegenWorld.invokedNames[member.name];
     if (selectors == null) return;
+    // Keep a cache of which stubs have already been generated, to
+    // avoid duplicates. Note that even if selectors are
+    // canonicalized, we would still need this cache: a typed selector
+    // on A and a typed selector on B could yield the same stub.
+    Set<String> generatedStubNames = new Set<String>();
     for (Selector selector in selectors) {
       if (!selector.applies(member, compiler)) continue;
-      addParameterStub(member, selector, defineInstanceMember);
+      addParameterStub(
+          member, selector, defineInstanceMember, generatedStubNames);
     }
   }
 
   bool instanceFieldNeedsGetter(Element member) {
     assert(member.isField());
     return compiler.codegenWorld.hasInvokedGetter(member, compiler);
   }
 
   bool instanceFieldNeedsSetter(Element member) {
     assert(member.isField());
@@ skipping 887 matching lines @@
 const String HOOKS_API_USAGE = """
 // Generated by dart2js, the Dart to JavaScript compiler.
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;