add getSourceLocation from stepindex

src/code/sourceLocationTracker.js

@@ -36,6 +36,36 @@ SourceLocationTracker.prototype.getSourceLocation = function (address, index, co
   })
 }
 
+/**
+ * Return the source location associated with the given @arg pc
+ *
+ * @param {String} address - contract address from which the source location is retrieved
+ * @param {Int} vmtraceStepIndex - index of the current code in the vmtrace
+ * @param {Object} contractDetails - AST of compiled contracts
+ * @param {Function} cb - callback function
+ */
+SourceLocationTracker.prototype.getSourceLocation = function (address, vmtraceStepIndex, contractsDetails, cb) {
+  var self = this
+  this.codeManager.getCode(address, function (error, result) {
+    if (!error) {
+      var sourceMap = getSourceMap(address, result.bytecode, contractsDetails)
+      if (sourceMap) {
+        self.codeManager.getInstructionIndex(address, vmtraceStepIndex, function (error, index) {
+          if (error) {
+            cb(error)
+          } else {
+            cb(null, self.sourceMappingDecoder.atIndex(index, sourceMap))
+          }
+        })
+      } else {
+        cb('no srcmap associated with the code ' + address)
+      }
+    } else {
+      cb(error)
+    }
+  })
+}
+
 /**
  * backwards compatibility - attribute name will certainly be changed
  */