fix ZINTERSTORE where target is one of the source sets

Author: alicebob

cmd_sorted_set.go

@@ -433,9 +433,6 @@ func (m *Miniredis) makeCmdZinter(store bool) func(c *server.Peer, cmd string, a
 
 		withTx(m, c, func(c *server.Peer, ctx *connCtx) {
 			db := m.db(ctx.selectedDB)
-			if opts.Store {
-				db.del(opts.Destination, true)
-			}
 
 			// We collect everything and remove all keys which turned out not to be
 			// present in every set.
@@ -493,6 +490,7 @@ func (m *Miniredis) makeCmdZinter(store bool) func(c *server.Peer, cmd string, a
 
 			if opts.Store {
 				// ZINTERSTORE mode
+				db.del(opts.Destination, true)
 				db.ssetSet(opts.Destination, sset)
 				c.WriteInt(len(sset))
 				return

integration/sorted_set_test.go

@@ -854,6 +854,11 @@ func TestZinter(t *testing.T) {
 		c.Do("ZINTERSTORE", "dest", "2", "q1", "q2")
 		c.Do("ZRANGE", "dest", "0", "-1", "withscores")
 
+		// store into self
+		c.Do("ZINTERSTORE", "q1", "2", "q1", "q2")
+		c.Do("ZRANGE", "q1", "0", "-1", "withscores")
+		c.Do("SMEMBERS", "q2")
+
 		// Error cases
 		c.Error("wrong number", "ZINTERSTORE")
 		c.Error("wrong number", "ZINTERSTORE", "h")