text: // Copyright 2010 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
  //       with the distribution.
  //     * Neither the name of Google Inc. nor the names of its
  //       contributors may be used to endorse or promote products derived
  //       from this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  // LiveEdit feature implementation. The script should be executed after
  // debug-debugger.js.
  
  
  // Changes script text and recompiles all relevant functions if possible.
  // 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. 
  //
  // @param {Script} script that is being changed
  // @param {Array} change_log a list that collects engineer-readable description
  //     of what happened.
  Debug.LiveEditChangeScript = function(script, change_pos, change_len, new_str,
      change_log) {
  
    // So far the function works as namespace.
    var liveedit = Debug.LiveEditChangeScript;
    var Assert = liveedit.Assert;
  
    // Fully compiles source string as a script. Returns Array of
    // FunctionCompileInfo -- a descriptions of all functions of the script.
    // Elements of array are ordered by start positions of functions (from top
    // to bottom) in the source. Fields outer_index and next_sibling_index help
    // to navigate the nesting structure of functions.
    // 
    // The script is used for compilation, because it produces code that 
    // needs to be linked with some particular script (for nested functions). 
    function DebugGatherCompileInfo(source) {
      // Get function info, elements are partially sorted (it is a tree
      // of nested functions serialized as parent followed by serialized children.
      var raw_compile_info = %LiveEditGatherCompileInfo(script, source);
  
      // Sort function infos by start position field.
      var compile_info = new Array();
      var old_index_map = new Array();
      for (var i = 0; i < raw_compile_info.length; i++) {
          compile_info.push(new liveedit.FunctionCompileInfo(raw_compile_info[i]));
          old_index_map.push(i);
      }
      
      for (var i = 0; i < compile_info.length; i++) {
        var k = i;
        for (var j = i + 1; j < compile_info.length; j++) {
          if (compile_info[k].start_position > compile_info[j].start_position) {
            k = j;
          }
        }
        if (k != i) {
          var temp_info = compile_info[k];
          var temp_index = old_index_map[k];
          compile_info[k] = compile_info[i];
          old_index_map[k] = old_index_map[i];
          compile_info[i] = temp_info;
          old_index_map[i] = temp_index;
        }
      }
  
      // After sorting update outer_inder field using old_index_map. Also
      // set next_sibling_index field.
      var current_index = 0;
  
      // The recursive function, that goes over all children of a particular
      // node (i.e. function info).
      function ResetIndexes(new_parent_index, old_parent_index) {
        var previous_sibling = -1;
        while (current_index < compile_info.length &&
            compile_info[current_index].outer_index == old_parent_index) {
          var saved_index = current_index;
          compile_info[saved_index].outer_index = new_parent_index;
          if (previous_sibling != -1) {
            compile_info[previous_sibling].next_sibling_index = saved_index;
          }
          previous_sibling = saved_index;
          current_index++;
          ResetIndexes(saved_index, old_index_map[saved_index]);
        }
        if (previous_sibling != -1) {
          compile_info[previous_sibling].next_sibling_index = -1;
        }
      }
      
      ResetIndexes(-1, -1);
      Assert(current_index == compile_info.length);
      
      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;
    // Finds SharedFunctionInfo that corresponds compile info with index
    // in old version of the script.
    function FindFunctionInfo(index) {
      var old_info = old_compile_info[index];
      for (var i = 0; i < shared_infos.length; i++) {
        var info = shared_infos[i];
        if (info.start_position == old_info.start_position && 
            info.end_position == old_info.end_position) {
          return info;
        }
      }
    }
  
    // 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;
      }
      return -1;
    }
    
    var position_change_array;
    var position_patch_report;
    function PatchPositions(new_info, shared_info) {
      if (!shared_info) {
        // TODO: explain what is happening.
        return;
      }
      %LiveEditPatchFunctionPositions(shared_info.raw_array,
          position_change_array);
      position_patch_report.push( { name: new_info.function_name } );
    }
    
    var link_to_old_script_report;
    var old_script;
    // 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 } );
    }
  
  
    
    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);
  
    var shared_infos = new Array();
  
    for (var i = 0; i < shared_raw_list.length; i++) {
      shared_infos.push(new liveedit.SharedInfoWrapper(shared_raw_list[i]));
    }
    
    // Gather compile information about old version of script.
    var old_compile_info = DebugGatherCompileInfo(old_source);
    
    // Gather compile information about new version of script.
    var new_compile_info;
    try {
      new_compile_info = DebugGatherCompileInfo(new_source);
    } catch (e) {
      throw new liveedit.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 (!liveedit.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);
    }
    
    // Check that function being patched is not currently on stack.
    liveedit.CheckStackActivations(
        [ FindFunctionInfo(function_being_patched) ], change_log );
    
  
    // Committing all changes.
    var old_script_name = liveedit.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));
      }
    }
  
    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);
    }
  }
  
  Debug.LiveEditChangeScript.Assert = function(condition, message) {
    if (!condition) {
      if (message) {
        throw "Assert " + message;
      } else {
        throw "Assert";
      }
    }
  }
      
  // An object describing function compilation details. Its index fields
  // apply to indexes inside array that stores these objects.
  Debug.LiveEditChangeScript.FunctionCompileInfo = function(raw_array) {
    this.function_name = raw_array[0];
    this.start_position = raw_array[1];
    this.end_position = raw_array[2];
    this.param_num = raw_array[3];
    this.code = raw_array[4];
    this.scope_info = raw_array[5];
    this.outer_index = raw_array[6];
    this.next_sibling_index = null;
    this.raw_array = raw_array;
  }
    
  // A structure describing SharedFunctionInfo.
  Debug.LiveEditChangeScript.SharedInfoWrapper = function(raw_array) {
    this.function_name = raw_array[0];
    this.start_position = raw_array[1];
    this.end_position = raw_array[2];
    this.info = raw_array[3];
    this.raw_array = raw_array;
  }
  
  // Adds a suffix to script name to mark that it is old version.
  Debug.LiveEditChangeScript.CreateNameForOldScript = function(script) {
    // TODO(635): try better than this; support several changes.
    return script.name + " (old)";
  }
  
  // Compares a function interface old and new version, whether it
  // changed or not.
  Debug.LiveEditChangeScript.CompareFunctionExpectations =
      function(function_info1, function_info2) {
    // Check that function has the same number of parameters (there may exist
    // an adapter, that won't survive function parameter number change).
    if (function_info1.param_num != function_info2.param_num) {
      return false;
    }
    var scope_info1 = function_info1.scope_info;
    var scope_info2 = function_info2.scope_info;
    
    if (!scope_info1) {
      return !scope_info2;
    }
    
    if (scope_info1.length != scope_info2.length) {
      return false;
    }
  
    // Check that outer scope structure is not changed. Otherwise the function
    // will not properly work with existing scopes.
    return scope_info1.toString() == scope_info2.toString(); 
  }
  
  // For array of wrapped shared function infos checks that none of them
  // have activations on stack (of any thread). Throws a Failure exception
  // if this proves to be false.
  Debug.LiveEditChangeScript.CheckStackActivations = function(shared_wrapper_list,
                                                              change_log) {
    var liveedit = Debug.LiveEditChangeScript;
        
    var shared_list = new Array();
    for (var i = 0; i < shared_wrapper_list.length; i++) {
      shared_list[i] = shared_wrapper_list[i].info;
    }
    var result = %LiveEditCheckStackActivations(shared_list);
    var problems = new Array();
    for (var i = 0; i < shared_list.length; i++) {
      if (result[i] == liveedit.FunctionPatchabilityStatus.FUNCTION_BLOCKED_ON_STACK) {
        var shared = shared_list[i];
        var description = {
            name: shared.function_name,
            start_pos: shared.start_position, 
            end_pos: shared.end_position
        };
        problems.push(description);
      }
    }
    if (problems.length > 0) {
      change_log.push( { functions_on_stack: problems } );
      throw new liveedit.Failure("Blocked by functions on stack");
    }
  }
  
  // A copy of the FunctionPatchabilityStatus enum from liveedit.h
  Debug.LiveEditChangeScript.FunctionPatchabilityStatus = {
      FUNCTION_AVAILABLE_FOR_PATCH: 0,
      FUNCTION_BLOCKED_ON_STACK: 1
  }
  
  
  // A logical failure in liveedit process. This means that change_log
  // is valid and consistent description of what happened.
  Debug.LiveEditChangeScript.Failure = function(message) {
    this.message = message;
  }
  
  Debug.LiveEditChangeScript.Failure.prototype.toString = function() {
    return "LiveEdit Failure: " + this.message;     
  }
  
  // A testing entry.
  Debug.LiveEditChangeScript.GetPcFromSourcePos = function(func, source_pos) {
    return %GetFunctionCodePositionFromSource(func, source_pos);
  }
  