alter: add Handler::format()

Needed to get format fields during alter in #2754

src/box/engine.cc

@@ -270,6 +270,12 @@ Handler::bsize() const
 	return 0;
 }
 
+struct tuple_format *
+Handler::format()
+{
+	return NULL;
+}
+
 /* }}} DDL */
 
 /* {{{ Engine API */

src/box/engine.h

@@ -274,6 +274,14 @@ struct Handler {
 	/** Binary size of a space. */
 	virtual size_t
 	bsize() const;
+	/**
+	 * Get format of a space.
+	 * @retval not NULL Space format.
+	 * @retval     NULL Space has no format (Sysview engine,
+	 *         for example).
+	 */
+	virtual struct tuple_format *
+	format();
 
 	Engine *engine;
 };

src/box/memtx_space.cc

@@ -786,4 +786,10 @@ MemtxSpace::commitAlterSpace(struct space *old_space, struct space *new_space)
 			((MemtxSpace *)old_space->handler)->m_bsize;
 }
 
+struct tuple_format *
+MemtxSpace::format()
+{
+	return m_format;
+}
+
 /* }}} DDL */

src/box/memtx_space.h

@@ -106,6 +106,8 @@ struct MemtxSpace: public Handler {
 	updateBsize(const struct tuple *old_tuple,
 		    const struct tuple *new_tuple);
 
+	virtual struct tuple_format *
+	format() override;
 public:
 	/**
 	 * A pointer to replace function, set to different values

src/box/vinyl_space.cc

@@ -278,4 +278,10 @@ VinylSpace::commitAlterSpace(struct space *old_space, struct space *new_space)
 		diag_raise();
 }
 
+struct tuple_format *
+VinylSpace::format()
+{
+	return m_format;
+}
+
 /* }}} DDL */

src/box/vinyl_space.h

@@ -70,6 +70,8 @@ struct VinylSpace: public Handler {
 	 */
 	virtual void commitAlterSpace(struct space *old_space,
 				      struct space *new_space) override;
+	virtual struct tuple_format *
+	format() override;
 private:
 	struct tuple_format *m_format;
 };