From 28fbeb8e9dc4606ba07926dd48d1a6551a5cabfa Mon Sep 17 00:00:00 2001
From: Teon Banek <teon.banek@memgraph.io>
Date: Fri, 19 May 2017 16:01:01 +0200
Subject: [PATCH] Raise if MATCH is after OPTIONAL MATCH

Reviewers: florijan, mislav.bradac

Reviewed By: mislav.bradac

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D383
---
 src/query/frontend/ast/cypher_main_visitor.cpp | 14 ++++++++++++--
 tests/unit/cypher_main_visitor.cpp             |  6 ++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/query/frontend/ast/cypher_main_visitor.cpp b/src/query/frontend/ast/cypher_main_visitor.cpp
index f5ab0c273..00b801dc7 100644
--- a/src/query/frontend/ast/cypher_main_visitor.cpp
+++ b/src/query/frontend/ast/cypher_main_visitor.cpp
@@ -41,11 +41,21 @@ antlrcpp::Any CypherMainVisitor::visitSingleQuery(
   // consecutive SET clauses are undefined behaviour in neo4j.
   bool has_update = false;
   bool has_return = false;
+  bool has_optional_match = false;
   for (Clause *clause : query_->clauses_) {
-    if (dynamic_cast<Match *>(clause) || dynamic_cast<Unwind *>(clause)) {
+    if (dynamic_cast<Unwind *>(clause)) {
+      if (has_update || has_return) {
+        throw SemanticException("Unwind can't be after return or update clause");
+      }
+    } else if (auto *match = dynamic_cast<Match *>(clause)) {
       if (has_update || has_return) {
         throw SemanticException("Match can't be after return or update clause");
       }
+      if (match->optional_) {
+        has_optional_match = true;
+      } else if (has_optional_match) {
+        throw SemanticException("Match can't be after optional match");
+      }
     } else if (dynamic_cast<Create *>(clause) ||
                dynamic_cast<Delete *>(clause) ||
                dynamic_cast<SetProperty *>(clause) ||
@@ -67,7 +77,7 @@ antlrcpp::Any CypherMainVisitor::visitSingleQuery(
       if (has_return) {
         throw SemanticException("Return can't be before with");
       }
-      has_update = has_return = false;
+      has_update = has_return = has_optional_match = false;
     } else {
       debug_assert(false, "Can't happen");
     }
diff --git a/tests/unit/cypher_main_visitor.cpp b/tests/unit/cypher_main_visitor.cpp
index 733832614..f58332dbe 100644
--- a/tests/unit/cypher_main_visitor.cpp
+++ b/tests/unit/cypher_main_visitor.cpp
@@ -1095,6 +1095,12 @@ TEST(CypherMainVisitorTest, ClausesOrdering) {
   ASSERT_THROW(AstGenerator("RETURN 1 AS n UNWIND n AS x RETURN x"),
                SemanticException);
 
+  ASSERT_THROW(AstGenerator("OPTIONAL MATCH (n) MATCH (m) RETURN n, m"),
+               SemanticException);
+  AstGenerator("OPTIONAL MATCH (n) WITH n MATCH (m) RETURN n, m");
+  AstGenerator("OPTIONAL MATCH (n) OPTIONAL MATCH (m) RETURN n, m");
+  AstGenerator("MATCH (n) OPTIONAL MATCH (m) RETURN n, m");
+
   AstGenerator("CREATE (n)");
   ASSERT_THROW(AstGenerator("SET n:x MATCH (n) RETURN n"), SemanticException);
   AstGenerator("REMOVE n.x SET n.x = 1");