Reimplement stack manipulations for LiveEdit

src/liveedit-debugger.js

Index: src/liveedit-debugger.js
diff --git a/src/liveedit-debugger.js b/src/liveedit-debugger.js
index c8c6f082c03297d28ca895c8b70cd73345db1197..506fb5b665319af775ed343f080735a724fe5d76 100644
--- a/src/liveedit-debugger.js
+++ b/src/liveedit-debugger.js
@@ -138,77 +138,92 @@ Debug.LiveEdit = new function() {
     
     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_wrapper = replace_code_list[i].live_shared_info_wrapper; 
-      if (info_wrapper) {
-        replaced_function_infos.push(info_wrapper);
-      }
-    }
-
+    // Check whether the functions being patched are currently on stack.
+    var stack_info_wrapper =
+        CheckStackActivations(replace_code_list, change_log);
+    preview_description.stack_modified = !!stack_info_wrapper; 
+    
     // We haven't changed anything before this line yet.
     // Committing all changes.
-    
-    // Check that function being patched is not currently on stack or drop them.
-    var dropped_functions_number =
-        CheckStackActivations(replaced_function_infos, change_log);
-    
-    preview_description.stack_modified = dropped_functions_number != 0; 
-  
+
     // Start with breakpoints. Convert their line/column positions and 
     // temporary remove.
     var break_points_restorer = TemporaryRemoveBreakPoints(script, change_log);
-
-    var old_script;
-
-    // Create an old script only if there are function that should be linked
-    // to old version.
-    if (link_to_old_script_list.length == 0) {
-      %LiveEditReplaceScript(script, new_source, null);
-      old_script = void 0;
-    } else {
-      var old_script_name = CreateNameForOldScript(script);
-      
-      // Update the script text and create a new script representing an old
-      // version of the script.
-      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(link_to_old_script_list[i], old_script,
-            link_to_old_script_report);
+    try {
+      var old_script;
+  
+      // Create an old script only if there are function that should be linked
+      // to old version.
+      if (link_to_old_script_list.length == 0) {
+        %LiveEditReplaceScript(script, new_source, null);
+        old_script = void 0;
+      } else {
+        var old_script_name = CreateNameForOldScript(script);
+        
+        // Update the script text and create a new script representing an old
+        // version of the script.
+        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(link_to_old_script_list[i], old_script,
+              link_to_old_script_report);
+        }
+        
+        preview_description.created_script_name = old_script_name;
       }
       
-      preview_description.created_script_name = old_script_name;
-    }
-    
-    // Link to an actual script all the functions that we are going to use.
-    for (var i = 0; i < link_to_original_script_list.length; i++) {
-      %LiveEditFunctionSetScript(
-          link_to_original_script_list[i].info.shared_function_info, script);
-    }
+      // Link to an actual script all the functions that we are going to use.
+      for (var i = 0; i < link_to_original_script_list.length; i++) {
+        %LiveEditFunctionSetScript(
+            link_to_original_script_list[i].info.shared_function_info, script);
+      }
 
-    for (var i = 0; i < replace_code_list.length; i++) {
-      PatchFunctionCode(replace_code_list[i], change_log);
-    }
-  
-    var position_patch_report = new Array();
-    change_log.push( {position_patched: position_patch_report} );
+      // In the general case there are several functions to be patched
+      // and some of them are activated on the stack.
+      // We drop n topmost frames from the stack, while restaring the
+      // bottom frame. The bottom frame function always is in the patch
+      // list (otherwise there was no reason to touch it). We have to
+      // reset the stack and patch the function in one transaction.
+      // All other functions are patched later.        
+      var bottom_function_index; 
+      if (stack_info_wrapper) {
+        bottom_function_index = stack_info_wrapper.bottom_function_index;
+        // First we must patch the function that is being reset
+        // to start on stack. 
+        PatchFunctionCode(replace_code_list[bottom_function_index],
+            stack_info_wrapper.drop_data, change_log);
+      } else {
+        bottom_function_index = -1;
+      }
+
+      
+      for (var i = 0; i < replace_code_list.length; i++) {
+        if (i == bottom_function_index) {
+          // Skip the function that has already been patched.
+          continue;
+        }
+        PatchFunctionCode(replace_code_list[i], void 0, change_log);
+      }
     
-    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], diff_array,
-          position_patch_report);
+      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], diff_array,
+            position_patch_report);
+      }
+    } finally {    
+      break_points_restorer(pos_translator, old_script);
     }
     
-    break_points_restorer(pos_translator, old_script);
-    
     preview_description.updated = true;
     return preview_description;
   }
@@ -292,13 +307,13 @@ Debug.LiveEdit = new function() {
   }
 
   
-  // Replaces function's Code.
-  function PatchFunctionCode(old_node, change_log) {
+  // Replaces function's Code and optionally resets the stack.
+  function PatchFunctionCode(old_node, stack_drop_data, change_log) {
     var new_info = old_node.corresponding_node.info;
     var shared_info_wrapper = old_node.live_shared_info_wrapper;
     if (shared_info_wrapper) {
       %LiveEditReplaceFunctionCode(new_info.raw_array,
-          shared_info_wrapper.raw_array);
+          shared_info_wrapper.raw_array, stack_drop_data);
 
       // The function got a new code. However, this new code brings all new
       // instances of SharedFunctionInfo for nested functions. However,
@@ -814,6 +829,15 @@ Debug.LiveEdit = new function() {
     this.info = raw_array[3];
     this.raw_array = raw_array;
   }
+  
+  // Information about possible stack manipulations. Either
+  // success (drop_data is defined), failure (error_message is defined)
+  // or empty otherwise.
+  function StackInfoWrapper(raw_array) {
+    this.error_message = raw_array[0];
+    this.bottom_function_index = raw_array[1];
+    this.drop_data = raw_array[2];
+  }
 
   // Changes positions (including all statments) in function.
   function PatchPositions(old_info_node, diff_array, report_array) {
@@ -869,67 +893,35 @@ Debug.LiveEdit = new function() {
     return;
   }
   
-  // Minifier forward declaration.
-  var FunctionPatchabilityStatus;
-  
-  // For array of wrapped shared function infos checks that none of them
+  // For an array of function nodes checks that none of them
   // have activations on stack (of any thread). Throws a Failure exception
   // if this proves to be false.
-  function CheckStackActivations(shared_wrapper_list, change_log) {
+  // Returns StackInfoWrapper for future stack manipulations or
+  // nothing if there is nothing to do with stack.
+  function CheckStackActivations(function_node_list, change_log) {
     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 = %LiveEditCheckAndDropActivations(shared_list, true);
-    if (result[shared_list.length]) {
-      // Extra array element may contain error message.
-      throw new Failure(result[shared_list.length]);
-    }
-  
-    var problems = new Array();
-    var dropped = new Array();
-    for (var i = 0; i < shared_list.length; i++) {
-      var shared = shared_wrapper_list[i];
-      if (result[i] == FunctionPatchabilityStatus.REPLACED_ON_ACTIVE_STACK) {
-        dropped.push({ name: shared.function_name } );
-      } else if (result[i] != FunctionPatchabilityStatus.AVAILABLE_FOR_PATCH) {
-        var description = {
-            name: shared.function_name,
-            start_pos: shared.start_position, 
-            end_pos: shared.end_position,
-            replace_problem:
-                FunctionPatchabilityStatus.SymbolName(result[i])
-        };
-        problems.push(description);
+    for (var i = 0; i < function_node_list.length; i++) {
+      var info_wrapper = function_node_list[i].live_shared_info_wrapper; 
+      if (info_wrapper) {
+        shared_list[i] = info_wrapper.info;
       }
     }
-    if (dropped.length > 0) {
-      change_log.push({ dropped_from_stack: dropped });
+    var raw_data_array = %LiveEditCheckActivations(shared_list);
+    var stack_info_wrapper = new StackInfoWrapper(raw_data_array);
+    var bottom_function_index = stack_info_wrapper.bottom_function_index;
+    if (stack_info_wrapper.error_message) {
+      if (IS_NUMBER(bottom_function_index)) {
+        throw new Failure(stack_info_wrapper.error_message +
+            "; function=" + shared_list[bottom_function_index].function_name);
+      } else {
+        throw new Failure(stack_info_wrapper.error_message + ".");
+      }
     }
-    if (problems.length > 0) {
-      change_log.push( { functions_on_stack: problems } );
-      throw new Failure("Blocked by functions on stack");
+    if (IS_NUMBER(bottom_function_index)) {
+      return stack_info_wrapper;
+    } else {
+      return;
     }
-    
-    return dropped.length;
-  }
-  
-  // A copy of the FunctionPatchabilityStatus enum from liveedit.h
-  var FunctionPatchabilityStatus = {
-      AVAILABLE_FOR_PATCH: 1,
-      BLOCKED_ON_ACTIVE_STACK: 2,
-      BLOCKED_ON_OTHER_STACK: 3,
-      BLOCKED_UNDER_NATIVE_CODE: 4,
-      REPLACED_ON_ACTIVE_STACK: 5
-  }
-  
-  FunctionPatchabilityStatus.SymbolName = function(code) {
-    var enum = FunctionPatchabilityStatus;
-    for (name in enum) {
-      if (enum[name] == code) {
-        return name;
-      }
-    }      
   }