Convert callers of base::DeepCopy() to base::CreateDeepCopy() in //base

base/json/json_parser.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/json/json_parser.h"
 
 #include <cmath>
-#include <memory>
+#include <utility>
 
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/memory/ptr_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversion_utils.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/third_party/icu/icu_utf.h"
 #include "base/values.h"
 
 namespace base {
 namespace internal {
 
 namespace {
 
 const int kStackMaxDepth = 100;
 
 const int32_t kExtendedASCIIStart = 0x80;
 
-// This and the class below are used to own the JSON input string for when
-// string tokens are stored as StringPiece instead of std::string. This
-// optimization avoids about 2/3rds of string memory copies. The constructor
-// takes ownership of the input string. The real root value is Swap()ed into
-// the new instance.
+// DictionaryHiddenRootValue and ListHiddenRootValue are used in conjunction
+// with JSONStringValue as an optimization for reducing the number of string
+// copies. When this optimization is active, the parser uses a hidden root to
+// keep the original JSON input string live and creates JSONStringValue children
+// holding StringPiece references to the input string, avoiding about 2/3rds of
+// string memory copies. The real root value is Swap()ed into the new instance.
 class DictionaryHiddenRootValue : public DictionaryValue {
  public:
-  DictionaryHiddenRootValue(std::string* json, Value* root) : json_(json) {
+  DictionaryHiddenRootValue(std::unique_ptr<std::string> json,
+                            std::unique_ptr<Value> root)
+      : json_(std::move(json)) {
     DCHECK(root->IsType(Value::TYPE_DICTIONARY));
-    DictionaryValue::Swap(static_cast<DictionaryValue*>(root));
+    DictionaryValue::Swap(static_cast<DictionaryValue*>(root.get()));

[danakj, 2016/04/28 17:39:37]

This should be passing the unique_ptr. Can you TODO somewhere?

[dcheng, 2016/04/28 18:03:23]

Should it though? It's not really moving/taking ownership of it so much as
swapping the contents: after all, things like std::vector::swap() don't require
passing in an rvalue reference.

[danakj, 2016/04/28 18:09:19]

Oh I guess you're right yah, it's swapping stuff into this Value here. ok.

   }
 
   void Swap(DictionaryValue* other) override {
     DVLOG(1) << "Swap()ing a DictionaryValue inefficiently.";
 
     // First deep copy to convert JSONStringValue to std::string and swap that
     // copy with |other|, which contains the new contents of |this|.
-    std::unique_ptr<DictionaryValue> copy(DeepCopy());
+    std::unique_ptr<DictionaryValue> copy(CreateDeepCopy());
     copy->Swap(other);
 
     // Then erase the contents of the current dictionary and swap in the
     // new contents, originally from |other|.
     Clear();
     json_.reset();
     DictionaryValue::Swap(copy.get());
   }
 
   // Not overriding DictionaryValue::Remove because it just calls through to
   // the method below.
 
   bool RemoveWithoutPathExpansion(const std::string& key,
                                   std::unique_ptr<Value>* out) override {
     // If the caller won't take ownership of the removed value, just call up.
     if (!out)
       return DictionaryValue::RemoveWithoutPathExpansion(key, out);
 
     DVLOG(1) << "Remove()ing from a DictionaryValue inefficiently.";
 
     // Otherwise, remove the value while its still "owned" by this and copy it
     // to convert any JSONStringValues to std::string.
     std::unique_ptr<Value> out_owned;
     if (!DictionaryValue::RemoveWithoutPathExpansion(key, &out_owned))
       return false;
 
-    out->reset(out_owned->DeepCopy());
+    *out = out_owned->CreateDeepCopy();
 
     return true;
   }
 
  private:
   std::unique_ptr<std::string> json_;
 
   DISALLOW_COPY_AND_ASSIGN(DictionaryHiddenRootValue);
 };
 
 class ListHiddenRootValue : public ListValue {
  public:
-  ListHiddenRootValue(std::string* json, Value* root) : json_(json) {
+  ListHiddenRootValue(std::unique_ptr<std::string> json,
+                      std::unique_ptr<Value> root)
+      : json_(std::move(json)) {
     DCHECK(root->IsType(Value::TYPE_LIST));
-    ListValue::Swap(static_cast<ListValue*>(root));
+    ListValue::Swap(static_cast<ListValue*>(root.get()));

[danakj, 2016/04/28 17:39:37]

ditto

[dcheng, 2016/04/28 18:03:23]

See previous.

   }
 
   void Swap(ListValue* other) override {
     DVLOG(1) << "Swap()ing a ListValue inefficiently.";
 
     // First deep copy to convert JSONStringValue to std::string and swap that
     // copy with |other|, which contains the new contents of |this|.
-    std::unique_ptr<ListValue> copy(DeepCopy());
+    std::unique_ptr<ListValue> copy(CreateDeepCopy());
     copy->Swap(other);
 
     // Then erase the contents of the current list and swap in the new contents,
     // originally from |other|.
     Clear();
     json_.reset();
     ListValue::Swap(copy.get());
   }
 
   bool Remove(size_t index, std::unique_ptr<Value>* out) override {
     // If the caller won't take ownership of the removed value, just call up.
     if (!out)
       return ListValue::Remove(index, out);
 
     DVLOG(1) << "Remove()ing from a ListValue inefficiently.";
 
     // Otherwise, remove the value while its still "owned" by this and copy it
     // to convert any JSONStringValues to std::string.
     std::unique_ptr<Value> out_owned;
     if (!ListValue::Remove(index, &out_owned))

[danakj, 2016/04/28 17:39:37]

heh, we should just have this return std::unique_ptr and null means the same as
false currently

[dcheng, 2016/04/28 18:03:23]

Acknowledged.

       return false;
 
-    out->reset(out_owned->DeepCopy());
+    *out = out_owned->CreateDeepCopy();
 
     return true;
   }
 
  private:
   std::unique_ptr<std::string> json_;
 
   DISALLOW_COPY_AND_ASSIGN(ListHiddenRootValue);
 };
 
 // A variant on StringValue that uses StringPiece instead of copying the string
 // into the Value. This can only be stored in a child of hidden root (above),
 // otherwise the referenced string will not be guaranteed to outlive it.
 class JSONStringValue : public Value {
  public:
-  explicit JSONStringValue(const StringPiece& piece)
-      : Value(TYPE_STRING),
-        string_piece_(piece) {
-  }
+  explicit JSONStringValue(StringPiece piece)
+      : Value(TYPE_STRING), string_piece_(piece) {}

[danakj, 2016/04/28 17:39:37]

nit: move piece? (i know its the same as copy atm)

[dcheng, 2016/04/28 18:03:23]

Why though? copy on a StringPiece will be cheaper than move anyway.

[jbroman, 2016/04/28 18:06:18]

nit-nit: base::StringPiece explicitly promises in its header that it's
essentially free to copy and consists only of a pointer + length. Moving it feel
like writing using std::move on an int, gfx::Point, or similar.

[danakj, 2016/04/28 18:09:19]

Ah I see I see. #newtostrings. LGTM

 
   // Overridden from Value:
   bool GetAsString(std::string* out_value) const override {
     string_piece_.CopyToString(out_value);
     return true;
   }
   bool GetAsString(string16* out_value) const override {
     *out_value = UTF8ToUTF16(string_piece_);
     return true;
   }
@@ skipping 46 matching lines @@
       line_number_(0),
       index_last_line_(0),
       error_code_(JSONReader::JSON_NO_ERROR),
       error_line_(0),
       error_column_(0) {
 }
 
 JSONParser::~JSONParser() {
 }
 
-Value* JSONParser::Parse(const StringPiece& input) {
+std::unique_ptr<Value> JSONParser::Parse(StringPiece input) {
   std::unique_ptr<std::string> input_copy;
   // If the children of a JSON root can be detached, then hidden roots cannot
   // be used, so do not bother copying the input because StringPiece will not
   // be used anywhere.
   if (!(options_ & JSON_DETACHABLE_CHILDREN)) {
-    input_copy.reset(new std::string(input.as_string()));
+    input_copy = WrapUnique(new std::string(input.as_string()));
     start_pos_ = input_copy->data();
   } else {
     start_pos_ = input.data();
   }
   pos_ = start_pos_;
   end_pos_ = start_pos_ + input.length();
   index_ = 0;
   line_number_ = 1;
   index_last_line_ = 0;
 
   error_code_ = JSONReader::JSON_NO_ERROR;
   error_line_ = 0;
   error_column_ = 0;
 
   // When the input JSON string starts with a UTF-8 Byte-Order-Mark
   // <0xEF 0xBB 0xBF>, advance the start position to avoid the
   // ParseNextToken function mis-treating a Unicode BOM as an invalid
   // character and returning NULL.
   if (CanConsume(3) && static_cast<uint8_t>(*pos_) == 0xEF &&
       static_cast<uint8_t>(*(pos_ + 1)) == 0xBB &&
       static_cast<uint8_t>(*(pos_ + 2)) == 0xBF) {
     NextNChars(3);
   }
 
   // Parse the first and any nested tokens.
   std::unique_ptr<Value> root(ParseNextToken());
-  if (!root.get())
-    return NULL;
+  if (!root)
+    return nullptr;
 
   // Make sure the input stream is at an end.
   if (GetNextToken() != T_END_OF_INPUT) {
     if (!CanConsume(1) || (NextChar() && GetNextToken() != T_END_OF_INPUT)) {
       ReportError(JSONReader::JSON_UNEXPECTED_DATA_AFTER_ROOT, 1);
-      return NULL;
+      return nullptr;
     }
   }
 
   // Dictionaries and lists can contain JSONStringValues, so wrap them in a
   // hidden root.
   if (!(options_ & JSON_DETACHABLE_CHILDREN)) {
     if (root->IsType(Value::TYPE_DICTIONARY)) {
-      return new DictionaryHiddenRootValue(input_copy.release(), root.get());
+      return WrapUnique(new DictionaryHiddenRootValue(std::move(input_copy),
+                                                      std::move(root)));
     } else if (root->IsType(Value::TYPE_LIST)) {
-      return new ListHiddenRootValue(input_copy.release(), root.get());
+      return WrapUnique(
+          new ListHiddenRootValue(std::move(input_copy), std::move(root)));
     } else if (root->IsType(Value::TYPE_STRING)) {
       // A string type could be a JSONStringValue, but because there's no
       // corresponding HiddenRootValue, the memory will be lost. Deep copy to
       // preserve it.
-      return root->DeepCopy();
+      return root->CreateDeepCopy();
     }
   }
 
   // All other values can be returned directly.
-  return root.release();
+  return root;
 }
 
 JSONReader::JsonParseError JSONParser::error_code() const {
   return error_code_;
 }
 
 std::string JSONParser::GetErrorMessage() const {
   return FormatErrorMessage(error_line_, error_column_,
       JSONReader::ErrorCodeToString(error_code_));
 }
@@ skipping 697 matching lines @@
                                            const std::string& description) {
   if (line || column) {
     return StringPrintf("Line: %i, column: %i, %s",
         line, column, description.c_str());
   }
   return description;
 }
 
 }  // namespace internal
 }  // namespace base