Support multi-chunk differences

src/liveedit-debugger.js

Index: src/liveedit-debugger.js
diff --git a/src/liveedit-debugger.js b/src/liveedit-debugger.js
index d2aee87949b59f363f6e240798b5bf1452bda60a..8fbff41b4cce8c1dfbda47865b7a5c94edbc26c0 100644
--- a/src/liveedit-debugger.js
+++ b/src/liveedit-debugger.js
@@ -28,26 +28,52 @@
 // LiveEdit feature implementation. The script should be executed after
 // debug-debugger.js.
 
-// A LiveEdit namespace is declared inside a single function constructor.
+// A LiveEdit namespace. It contains functions that modifies JavaScript code
+// according to changes of script source (if possible).
+//
+// When new script source is put in, the difference is calculated textually,
+// in form of list of delete/add/change chunks. The functions that include
+// change chunk(s) get recompiled, or their enclosing functions are
+// recompiled instead.
+// If the function may not be recompiled (e.g. it was completely erased in new
+// version of the script) it remains unchanged, but the code that could
+// create a new instance of this function goes away. An old version of script
+// is created to back up this obsolete function.
+// All unchanged functions have their positions updated accordingly.
+//
+// LiveEdit namespace is declared inside a single function constructor.
 Debug.LiveEdit = new function() {
 
-  // Changes script text and recompiles all relevant functions if possible.
+  // Applies the change to the script.
   // The change is always a substring (change_pos, change_pos + change_len)
   // being replaced with a completely different string new_str.
-  //
-  // Only one function will have its Code changed in result of this function.
-  // All nested functions (should they have any instances at the moment) are
-  // left unchanged and re-linked to a newly created script instance
-  // representing old version of the source. (Generally speaking,
-  // during the change all nested functions are erased and completely different
-  // set of nested functions are introduced.) All other functions just have
-  // their positions updated.
+  // This API is a legacy and is obsolete.
   //
   // @param {Script} script that is being changed
   // @param {Array} change_log a list that collects engineer-readable
   //     description of what happened.
   function ApplyPatch(script, change_pos, change_len, new_str,
       change_log) {
+    var old_source = script.source;
+  
+    // Prepare new source string.
+    var new_source = old_source.substring(0, change_pos) +
+        new_str + old_source.substring(change_pos + change_len);
+    
+    return ApplyPatchMultiChunk(script,
+        [ change_pos, change_pos + change_len, change_pos + new_str.length],
+        new_source, change_log);
+  }
+  // Function is public.
+  this.ApplyPatch = ApplyPatch;
+
+  // Forward declaration for minifier.
+  var FunctionStatus;
+  
+  // Applies the change to the script.
+  // The change is in form of list of chunks encoded in a single array as
+  // a series of triplets (pos1_start, pos1_end, pos2_end)
+  function ApplyPatchMultiChunk(script, diff_array, new_source, change_log) {
 
     // Fully compiles source string as a script. Returns Array of
     // FunctionCompileInfo -- a descriptions of all functions of the script.
@@ -117,27 +143,6 @@ Debug.LiveEdit = new function() {
       return compile_info;
     }
   
-    // Given a positions, finds a function that fully includes the entire
-    // change.
-    function FindChangedFunction(compile_info, offset, len) {
-      // First condition: function should start before the change region.
-      // Function #0 (whole-script function) always does, but we want
-      // one, that is later in this list.
-      var index = 0;
-      while (index + 1 < compile_info.length &&
-          compile_info[index + 1].start_position <= offset) {
-        index++;
-      }
-      // Now we are at the last function that begins before the change
-      // region. The function that covers entire change region is either
-      // this function or the enclosing one.
-      for (; compile_info[index].end_position < offset + len;
-          index = compile_info[index].outer_index) {
-        Assert(index != -1);
-      }
-      return index;
-    }
-  
     // Variable forward declarations. Preprocessor "Minifier" needs them.
     var old_compile_info;
     var shared_infos;
@@ -156,34 +161,27 @@ Debug.LiveEdit = new function() {
   
     // Replaces function's Code.
     function PatchCode(new_info, shared_info) {
-      %LiveEditReplaceFunctionCode(new_info.raw_array, shared_info.raw_array);
-  
-      change_log.push( {function_patched: new_info.function_name} );
-    }
-  
-    var change_len_old;
-    var change_len_new;
-    // Translate position in old version of script into position in new
-    // version of script.
-    function PosTranslator(old_pos) {
-      if (old_pos <= change_pos) {
-        return old_pos;
-      }
-      if (old_pos >= change_pos + change_len_old) {
-        return old_pos + change_len_new - change_len_old;
+      if (shared_info) {
+        %LiveEditReplaceFunctionCode(new_info.raw_array, shared_info.raw_array);
+        change_log.push( {function_patched: new_info.function_name} );
+      } else {
+        change_log.push( {function_patched: new_info.function_name,
+            function_info_not_found: true} );
       }
-      return -1;
+  
     }
   
-    var position_change_array;
+    
     var position_patch_report;
-    function PatchPositions(new_info, shared_info) {
+    function PatchPositions(old_info, shared_info) {
       if (!shared_info) {
-        // TODO(LiveEdit): explain what is happening.
+        // TODO(LiveEdit): function is not compiled yet or is already collected.
+        position_patch_report.push( 
+            { name: old_info.function_name, info_not_found: true } );
         return;
       }
       var breakpoint_position_update = %LiveEditPatchFunctionPositions(
-          shared_info.raw_array, position_change_array);
+          shared_info.raw_array, diff_array);
       for (var i = 0; i < breakpoint_position_update.length; i += 2) {
         var new_pos = breakpoint_position_update[i];
         var break_point_object = breakpoint_position_update[i + 1];
@@ -191,7 +189,7 @@ Debug.LiveEdit = new function() {
             { from: break_point_object.source_position(), to: new_pos } } );
         break_point_object.updateSourcePosition(new_pos, script);
       }
-      position_patch_report.push( { name: new_info.function_name } );
+      position_patch_report.push( { name: old_info.function_name } );
     }
   
     var link_to_old_script_report;
@@ -199,22 +197,19 @@ Debug.LiveEdit = new function() {
     // Makes a function associated with another instance of a script (the
     // one representing its old version). This way the function still
     // may access its own text.
-    function LinkToOldScript(shared_info) {
-      %LiveEditRelinkFunctionToScript(shared_info.raw_array, old_script);
-  
-      link_to_old_script_report.push( { name: shared_info.function_name } );
+    function LinkToOldScript(shared_info, old_info_node) {
+      if (shared_info) {
+        %LiveEditRelinkFunctionToScript(shared_info.raw_array, old_script);
+        link_to_old_script_report.push( { name: shared_info.function_name } );
+      } else {
+        link_to_old_script_report.push(
+            { name: old_info_node.info.function_name, not_found: true } );
+      }
     }
-  
-  
+    
   
     var old_source = script.source;
-    var change_len_old = change_len;
-    var change_len_new = new_str.length;
-  
-    // Prepare new source string.
-    var new_source = old_source.substring(0, change_pos) +
-        new_str + old_source.substring(change_pos + change_len);
-  
+   
     // Find all SharedFunctionInfo's that are compiled from this script.
     var shared_raw_list = %LiveEditFindSharedFunctionInfosForScript(script);
   
@@ -234,94 +229,103 @@ Debug.LiveEdit = new function() {
     } catch (e) {
       throw new Failure("Failed to compile new version of script: " + e);
     }
-  
-    // An index of a single function, that is going to have its code replaced.
-    var function_being_patched =
-        FindChangedFunction(old_compile_info, change_pos, change_len_old);
-  
-    // In old and new script versions function with a change should have the
-    // same indexes.
-    var function_being_patched2 =
-        FindChangedFunction(new_compile_info, change_pos, change_len_new);
-    Assert(function_being_patched == function_being_patched2,
-           "inconsistent old/new compile info");
-  
-    // Check that function being patched has the same expectations in a new
-    // version. Otherwise we cannot safely patch its behavior and should
-    // choose the outer function instead.
-    while (!CompareFunctionExpectations(
-        old_compile_info[function_being_patched],
-        new_compile_info[function_being_patched])) {
-  
-      Assert(old_compile_info[function_being_patched].outer_index ==
-          new_compile_info[function_being_patched].outer_index);
-      function_being_patched =
-          old_compile_info[function_being_patched].outer_index;
-      Assert(function_being_patched != -1);
+    
+    var pos_translator = new PosTranslator(diff_array);
+
+    // Build tree structures for old and new versions of the script.
+    var root_old_node = BuildCodeInfoTree(old_compile_info);
+    var root_new_node = BuildCodeInfoTree(new_compile_info);
+
+    // Analyze changes.
+    MarkChangedFunctions(root_old_node, pos_translator.GetChunks());
+    FindCorrespondingFunctions(root_old_node, root_new_node);
+    
+    // Prepare to-do lists.
+    var replace_code_list = new Array();
+    var link_to_old_script_list = new Array();
+    var update_positions_list = new Array();
+
+    function HarvestTodo(old_node) {
+      function CollectDamaged(node) {
+        link_to_old_script_list.push(node);
+        for (var i = 0; i < node.children.length; i++) {
+          CollectDamaged(node.children[i]);
+        }
+      }
+      
+      if (old_node.status == FunctionStatus.DAMAGED) {
+        CollectDamaged(old_node);
+        return;
+      }
+      if (old_node.status == FunctionStatus.UNCHANGED) {
+        update_positions_list.push(old_node);
+      } else if (old_node.status == FunctionStatus.SOURCE_CHANGED) {
+        update_positions_list.push(old_node);
+      } else if (old_node.status == FunctionStatus.CHANGED) {
+        replace_code_list.push(old_node);
+      }
+      for (var i = 0; i < old_node.children.length; i++) {
+        HarvestTodo(old_node.children[i]);
+      }
     }
-  
+
+    HarvestTodo(root_old_node);
+    
+    // Collect shared infos for functions whose code need to be patched.
+    var replaced_function_infos = new Array();
+    for (var i = 0; i < replace_code_list.length; i++) {
+      var info = FindFunctionInfo(replace_code_list[i].array_index);
+      if (info) {
+        replaced_function_infos.push(info);
+      }
+    }
+
     // Check that function being patched is not currently on stack.
-    CheckStackActivations(
-        [ FindFunctionInfo(function_being_patched) ], change_log );
+    CheckStackActivations(replaced_function_infos, change_log);
   
   
+    // We haven't changed anything before this line yet.
     // Committing all changes.
-    var old_script_name = CreateNameForOldScript(script);
-  
-    // Update the script text and create a new script representing an old
-    // version of the script.
-    var old_script = %LiveEditReplaceScript(script, new_source,
-        old_script_name);
-  
-    PatchCode(new_compile_info[function_being_patched],
-        FindFunctionInfo(function_being_patched));
-  
-    var position_patch_report = new Array();
-    change_log.push( {position_patched: position_patch_report} );
-  
-    var position_change_array = [ change_pos,
-                                  change_pos + change_len_old,
-                                  change_pos + change_len_new ];
-  
-    // Update positions of all outer functions (i.e. all functions, that
-    // are partially below the function being patched).
-    for (var i = new_compile_info[function_being_patched].outer_index;
-        i != -1;
-        i = new_compile_info[i].outer_index) {
-      PatchPositions(new_compile_info[i], FindFunctionInfo(i));
-    }
-  
-    // Update positions of all functions that are fully below the function
-    // being patched.
-    var old_next_sibling =
-        old_compile_info[function_being_patched].next_sibling_index;
-    var new_next_sibling =
-        new_compile_info[function_being_patched].next_sibling_index;
-  
-    // We simply go over the tail of both old and new lists. Their tails should
-    // have an identical structure.
-    if (old_next_sibling == -1) {
-      Assert(new_next_sibling == -1);
-    } else {
-      Assert(old_compile_info.length - old_next_sibling ==
-          new_compile_info.length - new_next_sibling);
-  
-      for (var i = old_next_sibling, j = new_next_sibling;
-          i < old_compile_info.length; i++, j++) {
-        PatchPositions(new_compile_info[j], FindFunctionInfo(i));
+
+    // Create old script if there are function linked to old version.
+    if (link_to_old_script_list.length > 0) {
+      var old_script_name = CreateNameForOldScript(script);
+      
+      // Update the script text and create a new script representing an old
+      // version of the script.
+      var old_script = %LiveEditReplaceScript(script, new_source,
+          old_script_name);
+      
+      var link_to_old_script_report = new Array();
+      change_log.push( { linked_to_old_script: link_to_old_script_report } );
+    
+      // We need to link to old script all former nested functions.
+      for (var i = 0; i < link_to_old_script_list.length; i++) {
+        LinkToOldScript(
+            FindFunctionInfo(link_to_old_script_list[i].array_index),
+            link_to_old_script_list[i]);
       }
     }
+    
+
+    for (var i = 0; i < replace_code_list.length; i++) {
+      PatchCode(replace_code_list[i].corresponding_node.info,
+          FindFunctionInfo(replace_code_list[i].array_index));
+    }
   
-    var link_to_old_script_report = new Array();
-    change_log.push( { linked_to_old_script: link_to_old_script_report } );
-  
-    // We need to link to old script all former nested functions.
-    for (var i = function_being_patched + 1; i < old_next_sibling; i++) {
-      LinkToOldScript(FindFunctionInfo(i), old_script);
+    var position_patch_report = new Array();
+    change_log.push( {position_patched: position_patch_report} );
+    
+    for (var i = 0; i < update_positions_list.length; i++) {
+      // TODO(LiveEdit): take into account wether it's source_changed or
+      // unchanged and whether positions changed at all.
+      PatchPositions(update_positions_list[i].info,
+          FindFunctionInfo(update_positions_list[i].array_index));
     }
   }
   // Function is public.
-  this.ApplyPatch = ApplyPatch;
+  this.ApplyPatchMultiChunk = ApplyPatchMultiChunk;
+
   
   function Assert(condition, message) {
     if (!condition) {
@@ -332,6 +336,296 @@ Debug.LiveEdit = new function() {
       }
     }
   }
+
+  function DiffChunk(pos1, pos2, len1, len2) {
+    this.pos1 = pos1;
+    this.pos2 = pos2;
+    this.len1 = len1;
+    this.len2 = len2;
+  }
+  
+  function PosTranslator(diff_array) {
+    var chunks = new Array();
+    var pos1 = 0;
+    var pos2 = 0;
+    for (var i = 0; i < diff_array.length; i += 3) {
+      pos2 += diff_array[i] - pos1 + pos2;
+      pos1 = diff_array[i];
+      chunks.push(new DiffChunk(pos1, pos2, diff_array[i + 1] - pos1,
+          diff_array[i + 2] - pos2));
+      pos1 = diff_array[i + 1];
+      pos2 = diff_array[i + 2];
+    }
+    this.chunks = chunks;
+  }
+  PosTranslator.prototype.GetChunks = function() {
+    return this.chunks;
+  }
+  
+  PosTranslator.prototype.Translate = function(pos, inside_chunk_handler) {
+    var array = this.chunks; 
+    if (array.length == 0 || pos < array[0]) {
+      return pos;
+    }
+    var chunk_index1 = 0;
+    var chunk_index2 = array.length - 1;
+
+    while (chunk_index1 < chunk_index2) {
+      var middle_index = (chunk_index1 + chunk_index2) / 2;
+      if (pos < array[middle_index + 1].pos1) {
+        chunk_index2 = middle_index;
+      } else {
+        chunk_index1 = middle_index + 1;
+      }
+    }
+    var chunk = array[chunk_index1];
+    if (pos >= chunk.pos1 + chunk.len1) {
+      return pos += chunk.pos2 + chunk.len2 - chunk.pos1 - chunk.len1; 
+    }
+    
+    if (!inside_chunk_handler) {
+      inside_chunk_handler = PosTranslator.default_inside_chunk_handler;
+    }
+    inside_chunk_handler(pos, chunk);
+  }
+
+  PosTranslator.default_inside_chunk_handler = function() {
+    Assert(false, "Cannot translate position in chaged area");
+  }
+  
+  var FunctionStatus = {
+      // No change to function or its inner functions; however its positions
+      // in script may have been shifted. 
+      UNCHANGED: "unchanged",
+      // The code of a function remains unchanged, but something happened inside
+      // some inner functions.
+      SOURCE_CHANGED: "source changed",
+      // The code of a function is changed or some nested function cannot be
+      // properly patched so this function must be recompiled.
+      CHANGED: "changed",
+      // Function is changed but cannot be patched.
+      DAMAGED: "damaged"
+  }
+  
+  function CodeInfoTreeNode(code_info, children, array_index) {
+    this.info = code_info;
+    this.children = children;
+    // an index in array of compile_info
+    this.array_index = array_index; 
+    this.parent = void(0);
+    
+    this.status = FunctionStatus.UNCHANGED;
+    // Status explanation is used for debugging purposes and will be shown
+    // in user UI if some explanations are needed.
+    this.status_explanation = void(0);
+    this.new_start_pos = void(0);
+    this.new_end_pos = void(0);
+    this.corresponding_node = void(0);
+  }
+  
+  // From array of function infos that is implicitly a tree creates
+  // an actual tree of functions in script.
+  function BuildCodeInfoTree(code_info_array) {
+    // Throughtout all function we iterate over input array.
+    var index = 0;
+
+    // Recursive function that builds a branch of tree. 
+    function BuildNode() {
+      var my_index = index;
+      index++;
+      var child_array = new Array();
+      while (index < code_info_array.length &&
+          code_info_array[index].outer_index == my_index) {
+        child_array.push(BuildNode());
+      }
+      var node = new CodeInfoTreeNode(code_info_array[my_index], child_array,
+          my_index);
+      for (var i = 0; i < child_array.length; i++) {
+        child_array[i].parent = node;
+      }
+      return node;
+    }
+    
+    var root = BuildNode();
+    Assert(index == code_info_array.length);
+    return root;
+  }
+
+  // Applies a list of the textual diff chunks onto the tree of functions.
+  // Determines status of each function (from unchanged to damaged). However
+  // children of unchanged functions are ignored.
+  function MarkChangedFunctions(code_info_tree, chunks) {
+
+    // A convenient interator over diff chunks that also translates
+    // positions from old to new in a current non-changed part of script.
+    var chunk_it = new function() {
+      var chunk_index = 0;
+      var pos_diff = 0;
+      this.current = function() { return chunks[chunk_index]; }
+      this.next = function() {
+        var chunk = chunks[chunk_index];
+        pos_diff = chunk.pos2 + chunk.len2 - (chunk.pos1 + chunk.len1); 
+        chunk_index++;
+      }
+      this.done = function() { return chunk_index >= chunks.length; }
+      this.TranslatePos = function(pos) { return pos + pos_diff; }
+    };
+
+    // A recursive function that processes internals of a function and all its
+    // inner functions. Iterator chunk_it initially points to a chunk that is
+    // below function start.
+    function ProcessInternals(info_node) {
+      info_node.new_start_pos = chunk_it.TranslatePos(
+          info_node.info.start_position); 
+      var child_index = 0;
+      var code_changed = false;
+      var source_changed = false;
+      // Simultaneously iterates over child functions and over chunks.
+      while (!chunk_it.done() &&
+          chunk_it.current().pos1 < info_node.info.end_position) {
+        if (child_index < info_node.children.length) {
+          var child = info_node.children[child_index];
+          
+          if (child.info.end_position <= chunk_it.current().pos1) {
+            ProcessUnchangedChild(child);
+            child_index++;
+            continue;
+          } else if (child.info.start_position >=
+              chunk_it.current().pos1 + chunk_it.current().len1) {
+            code_changed = true;
+            chunk_it.next();
+            continue;
+          } else if (child.info.start_position <= chunk_it.current().pos1 &&
+              child.info.end_position >= chunk_it.current().pos1 +
+              chunk_it.current().len1) {
+            ProcessInternals(child);
+            source_changed = source_changed ||
+                ( child.status != FunctionStatus.UNCHANGED );
+            code_changed = code_changed ||
+                ( child.status == FunctionStatus.DAMAGED );
+            child_index++;
+            continue;
+          } else {
+            code_changed = true;
+            child.status = FunctionStatus.DAMAGED;
+            child.status_explanation =
+                "Text diff overlaps with function boundary";
+            child_index++;
+            continue;
+          }
+        } else {
+          if (chunk_it.current().pos1 + chunk_it.current().len1 <= 
+              info_node.info.end_position) {
+            info_node.status = FunctionStatus.CHANGED;
+            chunk_it.next();
+            continue;
+          } else {
+            info_node.status = FunctionStatus.DAMAGED;
+            info_node.status_explanation =
+                "Text diff overlaps with function boundary";
+            return;
+          }
+        }
+        Assert("Unreachable", false);
+      }
+      while (child_index < info_node.children.length) {
+        var child = info_node.children[child_index];
+        ProcessUnchangedChild(child);
+        child_index++;
+      }
+      if (code_changed) {
+        info_node.status = FunctionStatus.CHANGED;
+      } else if (source_changed) {
+        info_node.status = FunctionStatus.SOURCE_CHANGED;
+      }
+      info_node.new_end_pos =
+          chunk_it.TranslatePos(info_node.info.end_position); 
+    }
+    
+    function ProcessUnchangedChild(node) {
+      node.new_start_pos = chunk_it.TranslatePos(node.info.start_position);
+      node.new_end_pos = chunk_it.TranslatePos(node.info.end_position);
+    }
+    
+    ProcessInternals(code_info_tree);
+  }
+
+  // For ecah old function (if it is not damaged) tries to find a corresponding
+  // function in new script. Typically it should succeed (non-damaged functions
+  // by definition may only have changes inside their bodies). However there are
+  // reasons for corresponence not to be found; function with unmodified text
+  // in new script may become enclosed into other function; the innocent change
+  // inside function body may in fact be something like "} function B() {" that
+  // splits a function into 2 functions.
+  function FindCorrespondingFunctions(old_code_tree, new_code_tree) {
+
+    // A recursive function that tries to find a correspondence for all
+    // child functions and for their inner functions.
+    function ProcessChildren(old_node, new_node) {
+      var old_children = old_node.children;
+      var new_children = new_node.children;
+
+      var old_index = 0;
+      var new_index = 0;
+      while (old_index < old_children.length) {
+        if (old_children[old_index].status == FunctionStatus.DAMAGED) {
+          old_index++;
+        } else if (new_index < new_children.length) {
+          if (new_children[new_index].info.start_position <
+              old_children[old_index].new_start_pos) {
+            new_index++;
+          } else if (new_children[new_index].info.start_position ==
+              old_children[old_index].new_start_pos) {
+            if (new_children[new_index].info.end_position ==
+                old_children[old_index].new_end_pos) {
+              old_children[old_index].corresponding_node =
+                  new_children[new_index];
+              if (old_children[old_index].status != FunctionStatus.UNCHANGED) {
+                ProcessChildren(old_children[old_index],
+                    new_children[new_index]);
+                if (old_children[old_index].status == FunctionStatus.DAMAGED) {
+                  old_node.status = FunctionStatus.CHANGED;
+                }
+              }
+            } else {
+              old_children[old_index].status = FunctionStatus.DAMAGED;
+              old_children[old_index].status_explanation =
+                  "No corresponding function in new script found";
+              old_node.status = FunctionStatus.CHANGED;
+            }
+            new_index++;
+            old_index++;
+          } else {
+            old_children[old_index].status = FunctionStatus.DAMAGED;
+            old_children[old_index].status_explanation =
+                "No corresponding function in new script found";
+            old_node.status = FunctionStatus.CHANGED;
+            old_index++;
+          }
+        } else {
+          old_children[old_index].status = FunctionStatus.DAMAGED;
+          old_children[old_index].status_explanation =
+              "No corresponding function in new script found";
+          old_node.status = FunctionStatus.CHANGED;
+          old_index++;
+        }
+      }
+      
+      if (old_node.status == FunctionStatus.CHANGED) {
+        if (!CompareFunctionExpectations(old_node.info, new_node.info)) {
+          old_node.status = FunctionStatus.DAMAGED;
+          old_node.status_explanation = "Changed code expectations";
+        }
+      }
+    }
+
+    ProcessChildren(old_code_tree, new_code_tree);
+    
+    old_code_tree.corresponding_node = new_code_tree;
+    Assert(old_code_tree.status != FunctionStatus.DAMAGED,
+        "Script became damaged");
+  }
+
   
   // An object describing function compilation details. Its index fields
   // apply to indexes inside array that stores these objects.
@@ -469,13 +763,12 @@ Debug.LiveEdit = new function() {
   // LiveEdit main entry point: changes a script text to a new string.
   function SetScriptSource(script, new_source, change_log) {
     var old_source = script.source;
-    var diff = FindSimpleDiff(old_source, new_source);
-    if (!diff) {
+    var diff = CompareStringsLinewise(old_source, new_source);
+    if (diff.length == 0) {
+      change_log.push( { empty_diff: true } );
       return;
     }
-    ApplyPatch(script, diff.change_pos, diff.old_len,
-        new_source.substring(diff.change_pos, diff.change_pos + diff.new_len),
-        change_log);
+    ApplyPatchMultiChunk(script, diff, new_source, change_log);
   }
   // Function is public.
   this.SetScriptSource = SetScriptSource;