add some minification transformers

lib/6to5/transformation/transformers/index.js

@@ -80,5 +80,10 @@ module.exports = {
   "spec.undefinedToVoid":                  require("./spec/undefined-to-void"),
 
   "minification.propertyLiterals":         require("./minification/property-literals"),
-  "minification.memberExpressionLiterals": require("./minification/member-expression-literals")
+  "minification.memberExpressionLiterals": require("./minification/member-expression-literals"),
+
+  "minification.removeDebugger":           require("./minification/remove-debugger"),
+  "minification.removeConsoleCalls":       require("./minification/remove-console-calls"),
+  "minification.deadCodeElimination":      require("./minification/dead-code-elimination"),
+  "minification.renameLocalVariables":     require("./minification/rename-local-variables")
 };

lib/6to5/transformation/transformers/minification/dead-code-elimination.js

@@ -0,0 +1,77 @@
+var t = require("../../../types");
+
+exports.optional = true;
+
+exports.ExpressionStatement = function (node, parent, scope, context, file) {
+  // remove consequenceless expressions such as local variables and literals
+  //
+  //   var foo = true; foo; -> var foo = true;
+  //   "foo"; ->
+  //
+
+  var expr = node.expression;
+  if (t.isLiteral(expr) || (t.isIdentifier(node) && t.hasBinding(node.name))) {
+    context.remove();
+  }
+};
+
+exports.IfStatement = {
+  exit: function (node, parent, scope, context, file) {
+    // todo: in scenarios where we can just return the consequent or
+    // alternate we should drop the block statement if it contains no
+    // block scoped variables
+
+    var consequent = node.consequent;
+    var alternate  = node.alternate;
+    var test       = node.test;
+
+    // we can check if a test will be truthy 100% and if so we can inline
+    // the consequent and completely ignore the alternate
+    //
+    //   if (true) { foo; } -> { foo; }
+    //   if ("foo") { foo; } -> { foo; }
+    //
+
+    if (t.isLiteral(test) && test.value) {
+      return alternate;
+    }
+
+    // we can check if a test will be falsy 100% and if so we can inline
+    // the alternate if there is one and completely remove the consequent
+    //
+    //   if ("") { bar; } else { foo; } -> { foo; }
+    //   if ("") { bar; } ->
+    //
+
+    if (t.isFalsyExpression(test)) {
+      if (alternate) {
+        return alternate;
+      } else {
+        return context.remove();
+      }
+    }
+
+    // remove alternate blocks that are empty
+    //
+    //   if (foo) { foo; } else {} -> if (foo) { foo; }
+    //
+
+    if (t.isBlockStatement(alternate) && !alternate.body.length) {
+      alternate = node.alternate = null;
+    }
+
+    // turn alternate blocks into a consequent and flip the test if the
+    // consequent block is empty
+    //
+    //   if (foo) {} else { bar; }
+    //   if (!foo) { bar; }
+    //
+
+    if (t.blockStatement(consequent) && !consequent.body.length &&
+        t.isBlockStatement(alternate) && alternate.body.length) {
+      node.consequent = node.alternate;
+      node.alternate  = null;
+      node.test       = t.unaryExpression("!", test, true);
+    }
+  }
+};

lib/6to5/transformation/transformers/minification/remove-console-calls.js

@@ -0,0 +1,13 @@
+"use strict";
+
+var t = require("../../../types");
+
+var isConsole = t.buildMatchMemberExpression("console", true);
+
+exports.optional = true;
+
+exports.CallExpression = function (node, parent, scope, context, file) {
+  if (isConsole(node.callee)) {
+    context.remove();
+  }
+};

lib/6to5/transformation/transformers/minification/remove-debugger.js

@@ -0,0 +1,9 @@
+var t = require("../../../types");
+
+exports.optional = true;
+
+exports.ExpressionStatement = function (node, parent, scope, context) {
+  if (t.isIdentifier(node.expression, { name: "debugger" })) {
+    context.remove();
+  }
+};

lib/6to5/transformation/transformers/minification/rename-local-variables.js

@@ -0,0 +1,10 @@
+var t = require("../../../types");
+
+exports.optional = true;
+
+exports.Scope = function () {
+  // todo: get all binding identifiers, generate compact names
+  // that wont collide and then call the remap identifier helper
+  // this transformer **has** to be ran last as it will absolutley
+  // destroy the scope tree
+};