Support ALTER THING .. DEPENDS ON EXTENSION

This introduces a new dependency type which marks an object as depending
on an extension, such that if the extension is dropped, the object
automatically goes away; and also, if the database is dumped, the object
is included in the dump output.  Currently the grammar supports this for
indexes, triggers, materialized views and functions only, although the
utility code is generic so adding support for more object types is a
matter of touching the parser rules only.

Author: Abhijit Menon-Sen
Reviewed-by: Alexander Korotkov, Álvaro Herrera
Discussion: http://www.postgresql.org/message-id/20160115062649.GA5068@toroid.org

src/include/nodes/parsenodes.h

@@ -2535,6 +2535,20 @@ typedef struct RenameStmt
 	bool		missing_ok;		/* skip error if missing? */
 } RenameStmt;
 
+/* ----------------------
+ * ALTER object DEPENDS ON EXTENSION extname
+ * ----------------------
+ */
+typedef struct AlterObjectDependsStmt
+{
+	NodeTag		type;
+	ObjectType	objectType;		/* OBJECT_FUNCTION, OBJECT_TRIGGER, etc */
+	RangeVar   *relation;		/* in case a table is involved */
+	List	   *objname;		/* name of the object */
+	List	   *objargs;		/* argument types, if applicable */
+	Value	   *extname;		/* extension name */
+} AlterObjectDependsStmt;
+
 /* ----------------------
  *		ALTER object SET SCHEMA Statement
  * ----------------------