Enable stepping into callback passed to builtins (e.g. Array.forEach).

src/string.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 248 matching lines @@
   if (start < 0) return subject;
   var end = start + search.length;
 
   var builder = new ReplaceResultBuilder(subject);
   // prefix
   builder.addSpecialSlice(0, start);
 
   // Compute the string to replace with.
   if (IS_SPEC_FUNCTION(replace)) {
     var receiver = %GetDefaultReceiver(replace);
+    // Prepare break slots for debugger step in.
+    if (%DebugStepIntoBuiltinCallback(replace)) {
+      %PrepareBreakSlotsForCallback(replace);
+    }
     builder.add(%_CallFunction(receiver,
                                search,
                                start,
                                subject,
                                replace));
   } else {
     reusableMatchInfo[CAPTURE0] = start;
     reusableMatchInfo[CAPTURE1] = end;
     replace = TO_STRING_INLINE(replace);
     ExpandReplacement(replace, subject, reusableMatchInfo, builder);
@@ skipping 148 matching lines @@
     // No matches at all.
     reusableReplaceArray = resultArray;
     return subject;
   }
   var len = res.length;
   var i = 0;
   if (NUMBER_OF_CAPTURES(lastMatchInfo) == 2) {
     var match_start = 0;
     var override = new InternalArray(null, 0, subject);
     var receiver = %GetDefaultReceiver(replace);
-    while (i < len) {
-      var elem = res[i];
-      if (%_IsSmi(elem)) {
-        if (elem > 0) {
-          match_start = (elem >> 11) + (elem & 0x7ff);
+    if (%DebugStepIntoBuiltinCallback(replace)) {
+      while (i < len) {
+        var elem = res[i];
+        if (%_IsSmi(elem)) {
+          if (elem > 0) {
+            match_start = (elem >> 11) + (elem & 0x7ff);
+          } else {
+            match_start = res[++i] - elem;
+          }
         } else {
-          match_start = res[++i] - elem;
+          override[0] = elem;
+          override[1] = match_start;
+          lastMatchInfoOverride = override;
+          %PrepareBreakSlotsForCallback(replace);
+          var func_result =
+              %_CallFunction(receiver, elem, match_start, subject, replace);
+          res[i] = TO_STRING_INLINE(func_result);
+          match_start += elem.length;
         }
-      } else {
-        override[0] = elem;
-        override[1] = match_start;
-        lastMatchInfoOverride = override;
-        var func_result =
-            %_CallFunction(receiver, elem, match_start, subject, replace);
-        res[i] = TO_STRING_INLINE(func_result);
-        match_start += elem.length;
+        i++;
       }
-      i++;
+    } else {
+      while (i < len) {
+        var elem = res[i];
+        if (%_IsSmi(elem)) {
+          if (elem > 0) {
+            match_start = (elem >> 11) + (elem & 0x7ff);
+          } else {
+            match_start = res[++i] - elem;
+          }
+        } else {
+          override[0] = elem;
+          override[1] = match_start;
+          lastMatchInfoOverride = override;
+          var func_result =
+              %_CallFunction(receiver, elem, match_start, subject, replace);
+          res[i] = TO_STRING_INLINE(func_result);
+          match_start += elem.length;
+        }
+        i++;
+      }
     }
   } else {
     var receiver = %GetDefaultReceiver(replace);
     while (i < len) {
       var elem = res[i];
       if (!%_IsSmi(elem)) {
         // elem must be an Array.
         // Use the apply argument as backing for global RegExp properties.
         lastMatchInfoOverride = elem;
         var func_result = %Apply(replace, receiver, elem, 0, elem.length);
@@ skipping 19 matching lines @@
   var endOfMatch = matchInfo[CAPTURE1];
   // Compute the parameter list consisting of the match, captures, index,
   // and subject for the replace function invocation.
   // The number of captures plus one for the match.
   var m = NUMBER_OF_CAPTURES(matchInfo) >> 1;
   var replacement;
   var receiver = %GetDefaultReceiver(replace);
   if (m == 1) {
     // No captures, only the match, which is always valid.
     var s = SubString(subject, index, endOfMatch);
+    // Prepare break slots for debugger step in.
+    if (%DebugStepIntoBuiltinCallback(replace)) {
+      %PrepareBreakSlotsForCallback(replace);
+    }
     // Don't call directly to avoid exposing the built-in global object.
-    replacement =
-        %_CallFunction(receiver, s, index, subject, replace);
+    replacement = %_CallFunction(receiver, s, index, subject, replace);
   } else {
     var parameters = new InternalArray(m + 2);
     for (var j = 0; j < m; j++) {
       parameters[j] = CaptureString(subject, matchInfo, j);
     }
     parameters[j] = index;
     parameters[j + 1] = subject;
 
     replacement = %Apply(replace, receiver, parameters, 0, j + 2);
   }
@@ skipping 505 matching lines @@
     "fixed", StringFixed,
     "italics", StringItalics,
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup
   ));
 }
 
 SetUpString();