Stop using raw pointer to share composer::Table.

Background:
composer::Table is shared across different components.
Though we would like to avoid shared object, Table is not copyable so there is no other way to share them at this moment. The internal data of the Table is managed by std::unique_ptr, which makes simple copying impossible. Furthermore, copying the table every time would result in a significant performance degradation. Style guide says that we prefer to use std::shared_ptr for shared memory object.
PiperOrigin-RevId: 730072127

src/composer/BUILD.bazel

@@ -111,6 +111,7 @@ mozc_cc_library(
         "//composer/internal:special_key",
         "//protocol:commands_cc_proto",
         "//protocol:config_cc_proto",
+        "@com_google_absl//absl/base:no_destructor",
         "@com_google_absl//absl/container:flat_hash_map",
         "@com_google_absl//absl/container:flat_hash_set",
         "@com_google_absl//absl/hash",

src/composer/composer.cc

@@ -33,6 +33,7 @@
 
 #include <cstddef>
 #include <cstdint>
+#include <memory>
 #include <string>
 #include <tuple>
 #include <unordered_map>
@@ -569,14 +570,16 @@ void ComposerData::GetSubTransliterations(
 // Composer
 
 Composer::Composer()
-    : Composer(Table::GetDefaultTable(), commands::Request::default_instance(),
+    : Composer(Table::GetSharedDefaultTable(),
+               commands::Request::default_instance(),
                config::ConfigHandler::DefaultConfig()) {}
 
 Composer::Composer(const commands::Request &request,
                    const config::Config &config)
-    : Composer(Table::GetDefaultTable(), request, config) {}
+    : Composer(Table::GetSharedDefaultTable(), request, config) {}
 
-Composer::Composer(const Table &table, const commands::Request &request,
+Composer::Composer(std::shared_ptr<const Table> table,
+                   const commands::Request &request,
                    const config::Config &config)
     : position_(0),
       input_mode_(transliteration::HIRAGANA),
@@ -588,16 +591,17 @@ Composer::Composer(const Table &table, const commands::Request &request,
       max_length_(kMaxPreeditLength),
       request_(&request),
       config_(&config),
-      table_(&table),
+      table_(table),
       is_new_input_(true) {
   SetInputMode(transliteration::HIRAGANA);
+  DCHECK(table_);
   Reset();
 }
 
 // static
 ComposerData Composer::CreateEmptyComposerData() {
-  static const absl::NoDestructor<Table> table;
-  static const absl::NoDestructor<Composition> composition(*table);
+  static const absl::NoDestructor<Composition> composition(
+      Table::GetSharedDefaultTable());
   return ComposerData(*composition, 0, transliteration::HIRAGANA,
                       commands::Context::NORMAL, "", {});
 }
@@ -624,9 +628,10 @@ void Composer::ReloadConfig() {
 
 bool Composer::Empty() const { return (GetLength() == 0); }
 
-void Composer::SetTable(const Table &table) {
-  table_ = &table;
-  composition_.SetTable(*table_);
+void Composer::SetTable(std::shared_ptr<const Table> table) {
+  table_ = table;
+  DCHECK(table_);
+  composition_.SetTable(table_);
 }
 
 void Composer::SetRequest(const commands::Request &request) {

src/composer/composer.h

@@ -55,11 +55,12 @@ namespace mozc {
 namespace composer {
 
 // ComposerData is a data structure that represents the current state of the
-// composer. It is used by Converter, Predictor and Rewriters as a const object.
+// composer. It is used by Converter, Predictor and Rewriters as a const
+// object.
 class ComposerData {
  public:
-  // This constructor is temporary and should be removed, when ConverterRequest
-  // is updated to use a const ComposerData.
+  // This constructor is temporary and should be removed, when
+  // ConverterRequest is updated to use a const ComposerData.
   ABSL_DEPRECATED("Do not use this constructor except in converter_request.h")
   ComposerData() = default;
 
@@ -144,8 +145,8 @@ class ComposerData {
 };
 
 // Composer is a class that manages the composing text. It provides methods to
-// edit the text by users. Composer creates ComposerData as the snapshot of the
-// current state of the composer.
+// edit the text by users. Composer creates ComposerData as the snapshot of
+// the current state of the composer.
 class Composer final {
  public:
   // Pseudo commands in composer.
@@ -155,7 +156,7 @@ class Composer final {
   };
 
   Composer();
-  Composer(const Table &table, const commands::Request &request,
+  Composer(std::shared_ptr<const Table> table, const commands::Request &request,
            const config::Config &config);
   // This constructor is for testing.
   ABSL_DEPRECATED("Use the constructor with Table")
@@ -188,7 +189,7 @@ class Composer final {
   // Check the preedit string is empty or not.
   bool Empty() const;
 
-  void SetTable(const Table &table);
+  void SetTable(std::shared_ptr<const Table> table);
 
   void SetRequest(const commands::Request &request);
   void SetConfig(const config::Config &config);
@@ -390,9 +391,17 @@ class Composer final {
 
   size_t max_length_;
 
+  // TODO(all): Stop using raw pointer to achieve shared ownership.
   const commands::Request *request_ = nullptr;
   const config::Config *config_ = nullptr;
-  const Table *table_ = nullptr;
+
+  // Though we would like to avoid shared object, Table is not copyable so
+  // there is no other way to share them at this moment. The internal data
+  // of the Table is managed by std::unique_ptr, which makes simple copying
+  // impossible. Furthermore, copying the table every time would result in
+  // a significant performance degradation. Style guide says that we prefer
+  // to use std::shared_ptr for shared object.
+  std::shared_ptr<const Table> table_;
 
   // Timestamp of last modified.
   int64_t timestamp_msec_ = 0;

src/composer/composer_main.cc

@@ -50,8 +50,8 @@ using ::mozc::config::Config;
 int main(int argc, char **argv) {
   mozc::InitMozc(argv[0], &argc, &argv);
 
-  mozc::composer::Table table;
-  table.LoadFromFile(absl::GetFlag(FLAGS_table).c_str());
+  auto table = std::make_shared<mozc::composer::Table>();
+  table->LoadFromFile(absl::GetFlag(FLAGS_table).c_str());
   auto composer = std::make_unique<mozc::composer::Composer>(
       table, Request::default_instance(), Config::default_instance());
 

src/composer/composer_test.cc

@@ -107,10 +107,10 @@ class ComposerTest : public ::testing::Test {
   ~ComposerTest() override = default;
 
   void SetUp() override {
-    table_ = std::make_unique<Table>();
+    table_ = std::make_shared<Table>();
     config_ = std::make_unique<Config>();
     request_ = std::make_unique<Request>();
-    composer_ = std::make_unique<Composer>(*table_, *request_, *config_);
+    composer_ = std::make_unique<Composer>(table_, *request_, *config_);
     CharacterFormManager::GetCharacterFormManager()->SetDefaultRule();
   }
 
@@ -123,7 +123,7 @@ class ComposerTest : public ::testing::Test {
   }
 
   std::unique_ptr<Composer> composer_;
-  std::unique_ptr<Table> table_;
+  std::shared_ptr<Table> table_;
   std::unique_ptr<Request> request_;
   std::unique_ptr<Config> config_;
 };
@@ -854,7 +854,7 @@ TEST_F(ComposerTest, InsertCharacterKeyEventWithInputMode) {
     EXPECT_EQ(composer_->GetInputMode(), transliteration::HIRAGANA);
   }
 
-  composer_ = std::make_unique<Composer>(*table_, *request_, *config_);
+  composer_ = std::make_unique<Composer>(table_, *request_, *config_);
 
   {
     // "a" → "あ" (Hiragana)
@@ -1256,7 +1256,7 @@ TEST_F(ComposerTest, AutoIMETurnOffEnabled) {
     EXPECT_EQ(composer_->GetInputMode(), transliteration::HIRAGANA);
   }
 
-  composer_ = std::make_unique<Composer>(*table_, *request_, *config_);
+  composer_ = std::make_unique<Composer>(table_, *request_, *config_);
 
   {  // google
     InsertKey("g", composer_.get());
@@ -1321,7 +1321,7 @@ TEST_F(ComposerTest, AutoIMETurnOffEnabled) {
   }
 
   config_->set_shift_key_mode_switch(Config::OFF);
-  composer_ = std::make_unique<Composer>(*table_, *request_, *config_);
+  composer_ = std::make_unique<Composer>(table_, *request_, *config_);
 
   {  // Google
     InsertKey("G", composer_.get());

src/composer/internal/char_chunk.cc

@@ -30,6 +30,7 @@
 #include "composer/internal/char_chunk.h"
 
 #include <cstddef>
+#include <memory>
 #include <string>
 #include <tuple>
 #include <utility>
@@ -111,13 +112,14 @@ bool GetFromPending(const Table *table, const absl::string_view key,
 }  // namespace
 
 CharChunk::CharChunk(Transliterators::Transliterator transliterator,
-                     const Table &table)
-    : table_(&table), transliterator_(transliterator) {
+                     std::shared_ptr<const Table> table)
+    : table_(table), transliterator_(transliterator) {
+  DCHECK(table_);
   DCHECK_NE(transliterator, Transliterators::LOCAL);
 }
 
 CharChunk::CharChunk(Transliterators::Transliterator transliterator)
-    : transliterator_(transliterator) {
+    : table_(Table::GetSharedDefaultTable()), transliterator_(transliterator) {
   DCHECK_NE(transliterator, Transliterators::LOCAL);
 }
 
@@ -244,7 +246,7 @@ absl::btree_set<std::string> CharChunk::GetExpandedResults() const {
       continue;
     }
     absl::btree_set<std::string> loop_result;
-    if (!GetFromPending(table_, entry->pending(), kMaxRecursion,
+    if (!GetFromPending(table_.get(), entry->pending(), kMaxRecursion,
                         &loop_result)) {
       continue;
     }
@@ -261,7 +263,7 @@ bool CharChunk::IsAppendable(Transliterators::Transliterator t12r,
                              const Table &table) const {
   return !pending_.empty() &&
          (t12r == Transliterators::LOCAL || t12r == transliterator_) &&
-         &table == table_;
+         &table == table_.get();
 }
 
 bool CharChunk::IsConvertible(Transliterators::Transliterator t12r,
@@ -565,7 +567,7 @@ absl::StatusOr<CharChunk> CharChunk::SplitChunk(
               DeleteSpecialKeys(conversion_ + pending_), &raw_lhs, &raw_rhs,
               &converted_lhs, &converted_rhs);
 
-  CharChunk left_new_chunk(transliterator_, *table_);
+  CharChunk left_new_chunk(transliterator_, table_);
   left_new_chunk.set_raw(raw_lhs);
   set_raw(std::move(raw_rhs));
 

src/composer/internal/char_chunk.h

@@ -35,8 +35,8 @@
 #include <tuple>
 #include <utility>
 
-#include "absl/container/btree_set.h"
 #include "absl/base/attributes.h"
+#include "absl/container/btree_set.h"
 #include "absl/status/statusor.h"
 #include "absl/strings/str_format.h"
 #include "absl/strings/string_view.h"
@@ -56,7 +56,8 @@ namespace composer {
 class CharChunk final {
  public:
   // LOCAL transliterator is not accepted.
-  CharChunk(Transliterators::Transliterator transliterator, const Table &table);
+  CharChunk(Transliterators::Transliterator transliterator,
+            std::shared_ptr<const Table> table);
   // This constructor is for testing.
   ABSL_DEPRECATED("Use the constructor with Table")
   explicit CharChunk(Transliterators::Transliterator transliterator);
@@ -142,7 +143,7 @@ class CharChunk final {
   Transliterators::Transliterator transliterator() const {
     return transliterator_;
   }
-  const Table *table() const { return table_; }
+  std::shared_ptr<const Table> table_for_testing() const { return table_; }
 
   const std::string &raw() const { return raw_; }
   template <typename String>
@@ -191,8 +192,9 @@ class CharChunk final {
     absl::Format(&sink,
                  "table = %p, raw = %s, conversion = %s, pending = %s, "
                  "ambiguous = %s, transliterator = %v, attributes = %v",
-                 chunk.table_, chunk.raw_, chunk.conversion_, chunk.pending_,
-                 chunk.ambiguous_, chunk.transliterator_, chunk.attributes_);
+                 chunk.table_.get(), chunk.raw_, chunk.conversion_,
+                 chunk.pending_, chunk.ambiguous_, chunk.transliterator_,
+                 chunk.attributes_);
   }
 
   // bool = should loop
@@ -202,7 +204,7 @@ class CharChunk final {
  private:
   void AddInputAndConvertedChar(CompositionInput *composition_input);
 
-  const Table *table_ = nullptr;
+  std::shared_ptr<const Table> table_;
 
   // There are four variables to represent a composing text:
   // `raw_`, `conversion_`, `pending_`, and `ambiguous_`.