bem-xjst: introduce this.stack() and stack flag (#333)

lib/bemxjst/context.js

@@ -9,6 +9,8 @@ function Context(bemxjst) {
   // Save current block until the next BEM entity
   this._currBlock = '';
 
+  this.stackTrace = [];
+
   this.elem = null;
   this.mods = {};
   this.elemMods = {};
@@ -57,3 +59,7 @@ Context.prototype.generateId = function() {
 Context.prototype.reapply = function(ctx) {
   return this._bemxjst.run(ctx);
 };
+
+Context.prototype.trace = function() {
+  return this.stackTrace;
+};

lib/bemxjst/match.js

@@ -208,6 +208,17 @@ Match.prototype.exec = function(context) {
   this.thrownError = null;
 
   var out;
+
+  if (this.bemxjst.options.trace) {
+    context.stackTrace.push({
+      mode: this.modeName,
+      block: context.block,
+      elem: context.elem,
+      mods: context.mods,
+      elemMods: context.elemMods
+    });
+  }
+
   if (typeof template.body === 'function')
     out = this.tryCatch(template.body, context);
   else

test/bemcontext-trace-test.js

@@ -0,0 +1,30 @@
+var fixtures = require('./fixtures')('bemhtml');
+var test = fixtures.test;
+
+describe('BEMContext this.trace()', function() {
+  it('should have proper this.trace() without option', function() {
+    test(function() {
+      block('b1').content()({ block: 'b2' });
+      block('b2').content()(function() {
+        return JSON.stringify(this.trace());
+      });
+    }, { block: 'b1' },
+    '<div class="b1">' +
+      '<div class="b2">[]</div></div>');
+  });
+
+  it('should have proper this.trace() with option', function() {
+    test(function() {
+      block('b1').content()({ block: 'b2' });
+      block('b2').content()(function() {
+        return JSON.stringify(this.trace());
+      });
+    }, { block: 'b1' },
+    '<div class="b1">' +
+      '<div class="b2">[' +
+        '{"mode":"content","block":"b1","mods":{},"elemMods":{}},' +
+        '{"mode":"content","block":"b2","mods":{},"elemMods":{}}' +
+       ']</div></div>',
+    { trace: true });
+  });
+});