Basic implementation of liveedit feature

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) {
+
+  function Assert(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.
+  function FunctionCompileInfo(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.
+  function SharedInfoWrapper(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;
+  }
+  
+
+  // 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 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;
+  }
+
+  // Compares a function interface old and new version, whether it
+  // changed or not.
+  function CompareFunctionExpectations(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(); 
+  }
+  
+  // 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);
+  
+  // 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 "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);
+  }
+  
+  // TODO: Need to check here that there are no activations of the function
+  // being patched on stack.  
+
+  // Committing all changes.
+  var old_script_name = script.name + " (old)";
+
+  // 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 shared_infos = new Array();
+
+  for (var i = 0; i < shared_raw_list.length; i++) {
+    shared_infos.push(new SharedInfoWrapper(shared_raw_list[i]));
+  }
+
+  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);
+  }
+}
+