Use jstranform instead of recast

This gains us a massive speedup, envify w/ recast takes almost 7 secs on my mba
when browserifying React codebase. While envify w/ jstransform takes this down
to 1.5 sec (pre-recast speed) and deliver the same advantages as recast
transform (preserves code formatting).

custom.js

@@ -1,11 +1,9 @@
 var through = require('through')
-  , recast = require('recast')
   , xtend = require('xtend')
+  , jstransform = require('jstransform')
+  , createVisitors = require('./visitors')
 
-var types = recast.types.namedTypes
-  , build = recast.types.builders
-  , traverse = recast.types.traverse
-  , processEnvPattern = /\bprocess\.env\b/
+var processEnvPattern = /\bprocess\.env\b/
 
 module.exports = function(rootEnv) {
   rootEnv = rootEnv || process.env || {}
@@ -28,28 +26,7 @@ module.exports = function(rootEnv) {
       var source = buffer.join('')
 
       if (processEnvPattern.test(source)) {
-        var ast = recast.parse(source)
-
-        traverse(ast, function(node) {
-          if (
-               types.MemberExpression.check(node)
-            && !node.computed
-            && types.Identifier.check(node.property)
-            && types.MemberExpression.check(node.object)
-            && types.Identifier.check(node.object.object)
-            && node.object.object.name === 'process'
-            && types.Identifier.check(node.object.property)
-            && node.object.property.name === 'env'
-          ) {
-            var key = node.property.name
-            if (key in env) {
-              this.replace(build.literal(env[key]))
-              return false
-            }
-          }
-        });
-
-        source = recast.print(ast).code
+        source = jstransform.transform(createVisitors(env), source).code;
       }
 
       this.queue(source)

package.json

@@ -21,7 +21,8 @@
   "dependencies": {
     "xtend": "~2.1.2",
     "through": "~2.3.4",
-    "recast": "~0.5.6"
+    "esprima-fb": "~3001.1.0-dev-harmony-fb",
+    "jstransform": "~3.0.0"
   },
   "keywords": [
     "environment",

visitors.js

@@ -0,0 +1,32 @@
+var Syntax = require('esprima-fb').Syntax;
+var utils = require('jstransform/src/utils');
+
+function create(env) {
+
+  function visitProcessEnv(traverse, node, path, state) {
+    var key = node.property.name;
+    if (env[key] !== undefined) {
+      utils.catchup(node.range[0], state);
+      utils.append(JSON.stringify(env[key]), state);
+      utils.move(node.range[1], state);
+    }
+    return false;
+  }
+
+  visitProcessEnv.test = function(node, path, state) {
+    return (
+      node.type === Syntax.MemberExpression
+      && !node.computed
+      && node.property.type === Syntax.Identifier
+      && node.object.type === Syntax.MemberExpression
+      && node.object.object.type === Syntax.Identifier
+      && node.object.object.name === 'process'
+      && node.object.property.type === Syntax.Identifier
+      && node.object.property.name === 'env'
+    )
+  };
+
+  return [visitProcessEnv];
+}
+
+module.exports = create;