Add minifying renamer to the JS printer so locals are called z0, z1, z2, etc.

lib/compiler/implementation/js/printer.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.
 
 class Printer implements NodeVisitor {
   final bool shouldCompressOutput;
   leg.Compiler compiler;
   leg.CodeBuffer outBuffer;
   int indentLevel = 0;
   bool inForInit = false;
   bool atStatementBegin = false;
   final DanglingElseVisitor danglingElseVisitor;
+  final Namer namer;
 
   Printer(leg.Compiler compiler)
       : shouldCompressOutput = compiler.enableMinification,
         this.compiler = compiler,
         outBuffer = new leg.CodeBuffer(),
-        danglingElseVisitor = new DanglingElseVisitor(compiler);
+        danglingElseVisitor = new DanglingElseVisitor(compiler),
+        namer = DetermineRenamer(compiler.enableMinification);
+  
+  static Namer DetermineRenamer(bool shouldCompressOutput) {

[kasperl, 2012/10/10 08:46:55]

This should have been determineRenamer not DetermineRenamer.

+    return shouldCompressOutput ? new MinifyRenamer() : new IdentityNamer();
+  }
 
   void spaceOut() {
     if (!shouldCompressOutput) out(" ");
   }
   void lineOut() {
     if (!shouldCompressOutput) out("\n");
   }
 
   String lastAddedString = null;
   int get lastCharCode {
@@ skipping 316 matching lines @@
   }
 
   void functionOut(Fun fun, Node name) {
     out("function");
     if (name != null) {
       out(" ");
       // Name must be a [Decl]. Therefore only test for primary expressions.
       visitNestedExpression(name, PRIMARY,
                             newInForInit: false, newAtStatementBegin: false);
     }
+    namer.enterScope();
     out("(");
     if (fun.params != null) {
       visitCommaSeparated(fun.params, PRIMARY,
                           newInForInit: false, newAtStatementBegin: false);
     }
     out(")");
     blockBody(fun.body, needsSeparation: false, needsNewline: false);
+    namer.leaveScope();
   }
 
   visitFunctionDeclaration(FunctionDeclaration declaration) {
     indent();
     functionOut(declaration.function, declaration.name);
     lineOut();
   }
 
   visitNestedExpression(Expression node, int requiredPrecedence,
                         [bool newInForInit, bool newAtStatementBegin]) {
@@ skipping 217 matching lines @@
   }
 
   visitPostfix(Postfix postfix) {
     visitNestedExpression(postfix.argument, LEFT_HAND_SIDE,
                           newInForInit: inForInit,
                           newAtStatementBegin: atStatementBegin);
     out(postfix.op);
   }
 
   visitVariableUse(VariableUse ref) {
-    out(ref.name);
+    out(namer.getName(ref.name));
   }
 
   visitThis(This node) {
     out("this");
   }
 
   visitVariableDeclaration(VariableDeclaration decl) {
-    out(decl.name);
+    out(namer.declareName(decl.name));
   }
 
   visitParameter(Parameter param) {
-    out(param.name);
+    out(namer.declareName(param.name));
   }
 
   bool isDigit(int charCode) {
     return charCodes.$0 <= charCode && charCode <= charCodes.$9;
   }
 
   bool isValidJavaScriptId(String field) {
     if (field.length < 3) return false;
     // Ignore the leading and trailing string-delimiter.
     for (int i = 1; i < field.length - 1; i++) {
@@ skipping 196 matching lines @@
   bool visitExpression(Expression node) => false;
 }
 
 
 leg.CodeBuffer prettyPrint(Node node,
                            leg.Compiler compiler) {
   Printer printer = new Printer(compiler);
   printer.visit(node);
   return printer.outBuffer;
 }
+
+
+abstract class Namer {
+  String getName(String oldName);
+  String declareName(String oldName);
+  void enterScope();
+  void leaveScope();
+}
+
+
+class IdentityNamer implements Namer {
+  String getName(String oldName) => oldName;
+  String declareName(String oldName) => oldName;
+  void enterScope() {}
+  void leaveScope() {}
+}
+
+
+class MinifyRenamer implements Namer {
+  final List<Map<String, String>> maps;
+  final List<int> nameNumberStack;
+  int nameNumber;
+
+  MinifyRenamer() : maps = [], nameNumberStack = [], nameNumber = 0;

[kasperl, 2012/10/10 08:46:55]

All these initialization expressions can be safely moved to the definition of
the fields.

+
+  void enterScope() {
+    maps.add(new Map<String, String>());
+    nameNumberStack.add(nameNumber);
+  }
+
+  void leaveScope() {
+    maps.removeLast();
+    nameNumber = nameNumberStack.removeLast();
+  }
+
+  String getName(String oldName) {
+    for (int i = maps.length - 1; i >= 0; i--) {
+      var map = maps[i];
+      var replacement = map[oldName];
+      if (replacement != null) return replacement;
+    }
+    return oldName;
+  }
+
+  String declareName(String oldName) {
+    if (maps.length == 0) return oldName;

[kasperl, 2012/10/10 08:46:55]

maps.isEmpty()

+    var newName = "z${nameNumber++}";
+    maps.last()[oldName] = newName;
+    return newName;
+  }
+
+}