Add missing IsDefaultValue to SettingDesc, from upstream

src/settings.cpp

@@ -831,6 +831,12 @@ bool IntSettingDesc::IsSameValue(const IniItem *item, void *object) const
 	return item_value == object_value;
 }
 
+bool IntSettingDesc::IsDefaultValue(void *object) const
+{
+	int32_t object_value = this->Read(object);
+	return this->def == object_value;
+}
+
 void StringSettingDesc::FormatValue(char *buf, const char *last, const void *object) const
 {
 	const std::string &str = this->Read(object);
@@ -859,12 +865,24 @@ bool StringSettingDesc::IsSameValue(const IniItem *item, void *object) const
 	return item->value->compare(str) == 0;
 }
 
+bool StringSettingDesc::IsDefaultValue(void *object) const
+{
+	const std::string &str = this->Read(object);
+	return this->def == str;
+}
+
 bool ListSettingDesc::IsSameValue(const IniItem *item, void *object) const
 {
 	/* Checking for equality is way more expensive than just writing the value. */
 	return false;
 }
 
+bool ListSettingDesc::IsDefaultValue(void *) const
+{
+	/* Defaults of lists are often complicated, and hard to compare. */
+	return false;
+}
+
 /**
  * Loads all items from a 'grpname' section into a list
  * The list parameter can be a nullptr pointer, in this case nothing will be

src/settings_internal.h

@@ -165,6 +165,14 @@ struct SettingDesc {
 	 * @return True if the value is definitely the same (might be false when the same).
 	 */
 	virtual bool IsSameValue(const IniItem *item, void *object) const = 0;
+
+	/**
+	 * Check whether the value is the same as the default value.
+	 *
+	 * @param object The object the setting is in.
+	 * @return true iff the value is the default value.
+	 */
+	virtual bool IsDefaultValue(void *object) const = 0;
 };
 
 /** Base integer type, including boolean, settings. Only these are shown in the settings UI. */
@@ -219,6 +227,7 @@ struct IntSettingDesc : SettingDesc {
 	virtual void FormatIntValue(char *buf, const char *last, uint32 value) const;
 	void ParseValue(const IniItem *item, void *object) const override;
 	bool IsSameValue(const IniItem *item, void *object) const override;
+	bool IsDefaultValue(void *object) const override;
 	int32 Read(const void *object) const;
 
 private:
@@ -309,6 +318,7 @@ struct StringSettingDesc : SettingDesc {
 	void FormatValue(char *buf, const char *last, const void *object) const override;
 	void ParseValue(const IniItem *item, void *object) const override;
 	bool IsSameValue(const IniItem *item, void *object) const override;
+	bool IsDefaultValue(void *object) const override;
 	const std::string &Read(const void *object) const;
 
 private:
@@ -326,6 +336,7 @@ struct ListSettingDesc : SettingDesc {
 	void FormatValue(char *buf, const char *last, const void *object) const override;
 	void ParseValue(const IniItem *item, void *object) const override;
 	bool IsSameValue(const IniItem *item, void *object) const override;
+	bool IsDefaultValue(void *object) const override;
 };
 
 /** Placeholder for settings that have been removed, but might still linger in the savegame. */
@@ -338,6 +349,7 @@ struct NullSettingDesc : SettingDesc {
 	void FormatValue(char *buf, const char *last, const void *object) const override { NOT_REACHED(); }
 	void ParseValue(const IniItem *item, void *object) const override { NOT_REACHED(); }
 	bool IsSameValue(const IniItem *item, void *object) const override { NOT_REACHED(); }
+	bool IsDefaultValue(void *object) const override { NOT_REACHED(); }
 };
 
 typedef std::initializer_list<std::unique_ptr<const SettingDesc>> SettingTable;