Use depths array rather than passing array args

Approximately doubles the throughput performance of depthed templates and clears the way for doing recursive path lookups in pathed mode.

lib/handlebars/compiler/javascript-compiler.js

@@ -69,6 +69,8 @@ JavaScriptCompiler.prototype = {
 
     this.compileChildren(environment, options);
 
+    this.useDepths = this.useDepths || environment.depths.list.length;
+
     var opcodes = environment.opcodes,
         opcode,
         i,
@@ -115,6 +117,9 @@ JavaScriptCompiler.prototype = {
       if (this.options.data) {
         ret.useData = true;
       }
+      if (this.useDepths) {
+        ret.depths = true;
+      }
 
       if (!asObject) {
         ret.compiler = JSON.stringify(ret.compiler);
@@ -151,8 +156,8 @@ JavaScriptCompiler.prototype = {
 
     var params = ["depth0", "helpers", "partials", "data"];
 
-    for(var i=0, l=this.environment.depths.list.length; i<l; i++) {
-      params.push("depth" + this.environment.depths.list[i]);
+    if (this.useDepths) {
+      params.push('depths');
     }
 
     // Perform a second pass over the output to merge content when possible
@@ -668,6 +673,8 @@ JavaScriptCompiler.prototype = {
         child.name = 'program' + index;
         this.context.programs[index] = compiler.compile(child, options, this.context, !this.precompile);
         this.context.environments[index] = child;
+
+        this.useDepths = this.useDepths || compiler.useDepths;
       } else {
         child.index = index;
         child.name = 'program' + index;
@@ -689,17 +696,17 @@ JavaScriptCompiler.prototype = {
     }
 
     var child = this.environment.children[guid],
-        depths = child.depths.list, depth;
+        depths = child.depths.list,
+        useDepths = this.useDepths,
+        depth;
 
     var programParams = [child.index, 'data'];
 
-    for(var i=0, l = depths.length; i<l; i++) {
-      depth = depths[i];
-
-      programParams.push('depth' + (depth - 1));
+    if (useDepths) {
+      programParams.push('depths');
     }
 
-    return (depths.length === 0 ? 'this.program(' : 'this.programWithDepth(') + programParams.join(', ') + ')';
+    return 'this.program(' + programParams.join(', ') + ')';
   },
 
   useRegister: function(name) {
@@ -847,7 +854,11 @@ JavaScriptCompiler.prototype = {
   },
 
   contextName: function(context) {
-    return 'depth' + context;
+    if (this.useDepths && context) {
+      return 'depths[' + context + ']';
+    } else {
+      return 'depth' + context;
+    }
   },
 
   quotedString: function(str) {