Make wrap functions more debuggable.

lodash.js

@@ -26,7 +26,7 @@
   /** Used as the internal argument placeholder. */
   var PLACEHOLDER = '__lodash_placeholder__';
 
-  /** Used to compose bitmasks for wrapper metadata. */
+  /** Used to compose bitmasks for function metadata. */
   var BIND_FLAG = 1,
       BIND_KEY_FLAG = 2,
       CURRY_BOUND_FLAG = 4,
@@ -66,6 +66,19 @@
       MAX_ARRAY_INDEX = MAX_ARRAY_LENGTH - 1,
       HALF_MAX_ARRAY_LENGTH = MAX_ARRAY_LENGTH >>> 1;
 
+  /** Used to associate wrap methods with their bit flags. */
+  var wrapFlags = [
+    ['ary', ARY_FLAG],
+    ['bind', BIND_FLAG],
+    ['bindKey', BIND_KEY_FLAG],
+    ['curry', CURRY_FLAG],
+    ['curryRight', CURRY_RIGHT_FLAG],
+    ['flip', FLIP_FLAG],
+    ['partial', PARTIAL_FLAG],
+    ['partialRight', PARTIAL_RIGHT_FLAG],
+    ['rearg', REARG_FLAG]
+  ];
+
   /** `Object#toString` result references. */
   var argsTag = '[object Arguments]',
       arrayTag = '[object Array]',
@@ -130,6 +143,10 @@
       reTrimStart = /^\s+/,
       reTrimEnd = /\s+$/;
 
+  /** Used to match wrap detail comments. */
+  var reWrapComment = /\{(?:\n\/\* \[wrapped with .+\] \*\/)?\n?/,
+      reWrapDetails = /\{\n\/\* \[wrapped with (.+)\] \*/;
+
   /** Used to match non-compound words composed of alphanumeric characters. */
   var reBasicWord = /[a-zA-Z0-9]+/g;
 
@@ -1366,6 +1383,14 @@
         WeakMap = getNative(context, 'WeakMap'),
         nativeCreate = getNative(context.Object, 'create');
 
+    /* Used to set `toString` methods. */
+    var defineProperty = (function() {
+      var func = getNative(context.Object, 'defineProperty'),
+          name = getNative.name;
+
+      return (name && name.length > 2) ? func : undefined;
+    }());
+
     /** Used to store function metadata. */
     var metaMap = WeakMap && new WeakMap;
 
@@ -5040,7 +5065,7 @@
         setData(result, newData);
       }
       result.placeholder = placeholder;
-      return result;
+      return setWrapToString(result, func, bitmask);
     }
 
     /**
@@ -5177,7 +5202,7 @@
         result = createHybrid.apply(undefined, newData);
       }
       var setter = data ? baseSetData : setData;
-      return setter(result, newData);
+      return setWrapToString(setter(result, newData), func, bitmask);
     }
 
     /**
@@ -6130,6 +6155,41 @@
       };
     }());
 
+    /**
+     * Sets the `toString` method of `wrapper` to mimic the source of `ref`
+     * with wrapper details added to a comment at the top of the source body.
+     *
+     * @private
+     * @param {Function} wrapper The function to modify.
+     * @param {Function} ref The reference function.
+     * @param {number} bitmask The bitmask flags. See `createWrap` for more details.
+     * @returns {Function} Returns `wrapper`.
+     */
+    var setWrapToString = !defineProperty ? identity : function(wrapper, ref, bitmask) {
+      var string = (ref + ''),
+          match = string.match(reWrapDetails),
+          details = match ? match[1].split(/, (?:& )| & /) : [];
+
+      arrayEach(wrapFlags, function(pair) {
+        if ((bitmask & pair[1]) && !arrayIncludes(details, '_.'+ pair[0])) {
+          details.push('_.' + pair[0]);
+        }
+      });
+
+      var length = details.length,
+          lastIndex = length - 1;
+
+      details[lastIndex] = (length > 1 ? '& ' : '') + details[lastIndex];
+      details = details.join(length > 2 ? ', ' : ' ');
+      string = string.replace(reWrapComment, '{\n/* [wrapped with ' + details + '] */\n');
+
+      return defineProperty(wrapper, 'toString', {
+        'configurable': true,
+        'enumerable': false,
+        'value': constant(string)
+      });
+    };
+
     /**
      * Converts `string` to a property path array.
      *