Implement Firestore DatabaseInfo and port both Database{Id,Info} C++ to the iOS code (#738)

* implement Firestore DatabaseInfo in C++

* temporary stash changes; blocking on the massive renaming of .m to .mm

* add database_info_test to project

* finish port DatabaseId and fix style, modular fixing DatabaseInfo

* port DatabaseInfo

* remove FSTDatabase{ID,Info} and their tests from project

* fix unit test

* use namespace alias

* use namespace alias, leftover

* address more changes

* refactoring to use raw pointer instead of value for property

* address changes

* remove self->

* fix style

* remove the name suffix Alloc

* fix a bug

2 files changed, 22 insertions, 7 deletions

diff --git a/Firestore/core/src/firebase/firestore/model/database_id.cc b/Firestore/core/src/firebase/firestore/model/database_id.cc
index af12d30..d7e8a85 100644
--- a/Firestore/core/src/firebase/firestore/model/database_id.cc
+++ b/Firestore/core/src/firebase/firestore/model/database_id.cc
@@ -31,10 +31,6 @@ DatabaseId::DatabaseId(const absl::string_view project_id,
   FIREBASE_ASSERT(!database_id.empty());
 }
 
-bool DatabaseId::IsDefaultDatabase() {
-  return database_id_ == kDefaultDatabaseId;
-}
-
 }  // namespace model
 }  // namespace firestore
 }  // namespace firebase
diff --git a/Firestore/core/src/firebase/firestore/model/database_id.h b/Firestore/core/src/firebase/firestore/model/database_id.h
index 48c547c..648f982 100644
--- a/Firestore/core/src/firebase/firestore/model/database_id.h
+++ b/Firestore/core/src/firebase/firestore/model/database_id.h
@@ -17,6 +17,8 @@
 #ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DATABASE_ID_H_
 #define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_DATABASE_ID_H_
 
+#include <stdint.h>
+
 #include <string>
 
 #include "absl/strings/string_view.h"
@@ -31,6 +33,12 @@ class DatabaseId {
   /** The default name for "unset" database ID in resource names. */
   static constexpr const char* kDefaultDatabaseId = "(default)";
 
+#if defined(__OBJC__)
+  // For objective-c++ initialization; to be removed after migration.
+  // Do NOT use in C++ code.
+  DatabaseId() = default;
+#endif  // defined(__OBJC__)
+
   /**
    * Creates and returns a new DatabaseId.
    *
@@ -49,13 +57,24 @@ class DatabaseId {
   }
 
   /** Whether this is the default database of the project. */
-  bool IsDefaultDatabase();
+  bool IsDefaultDatabase() const {
+    return database_id_ == kDefaultDatabaseId;
+  }
+
+#if defined(__OBJC__)
+  // For objective-c++ hash; to be removed after migration.
+  // Do NOT use in C++ code.
+  uint64_t Hash() const {
+    std::hash<std::string> hash_fn;
+    return hash_fn(project_id_) * 31u + hash_fn(database_id_);
+  }
+#endif  // defined(__OBJC__)
 
   friend bool operator<(const DatabaseId& lhs, const DatabaseId& rhs);
 
  private:
-  const std::string project_id_;
-  const std::string database_id_;
+  std::string project_id_;
+  std::string database_id_;
 };
 
 /** Compares against another DatabaseId. */