src/liveedit-delay.js

// 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-delay.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);
}