Correct the infinite loop when go zero steps in cycle. (vesoft-inc#2101)

* Correct the forever loop when go zero steps in cycle.

* Note the testing case.

* Correct.

Co-authored-by: dutor <440396+dutor@users.noreply.github.com>

src/graph/GoExecutor.cpp

@@ -96,6 +96,13 @@ void GoExecutor::execute() {
         return;
     }
 
+    if (steps_ == 0) {
+        // #2100
+        // TODO(shylock) unify the steps checking
+        onEmptyInputs();
+        return;
+    }
+
     status = setupStarts();
     if (!status.ok()) {
         doError(std::move(status));

src/graph/test/GoTest.cpp

@@ -2369,6 +2369,37 @@ TEST_P(GoTest, Contains) {
     }
 }
 
+TEST_P(GoTest, ZeroStep) {
+    // Zero step
+    {
+        // #2100
+        // A cycle traversal
+        cpp2::ExecutionResponse resp;
+        auto *fmt = "GO 0 STEPS FROM %ld OVER serve BIDIRECT";
+        auto query = folly::stringPrintf(fmt, players_["Tim Duncan"].vid());
+        auto code = client_->execute(query, resp);
+        ASSERT_EQ(cpp2::ErrorCode::SUCCEEDED, code);
+
+        // Empty response
+        std::vector<std::tuple<int64_t>> expected = {
+        };
+        ASSERT_TRUE(verifyResult(resp, expected));
+    }
+
+    {
+        // a normal traversal
+        cpp2::ExecutionResponse resp;
+        auto *fmt = "GO 0 STEPS FROM %ld OVER serve";
+        auto query = folly::stringPrintf(fmt, players_["Tim Duncan"].vid());
+        auto code = client_->execute(query, resp);
+        ASSERT_EQ(cpp2::ErrorCode::SUCCEEDED, code);
+
+        std::vector<std::tuple<int64_t>> expected = {
+        };
+        ASSERT_TRUE(verifyResult(resp, expected));
+    }
+}
+
 INSTANTIATE_TEST_CASE_P(IfPushdownFilter, GoTest, ::testing::Bool());
 }   // namespace graph
 }   // namespace nebula

src/parser/test/ParserTest.cpp

@@ -13,6 +13,18 @@
 namespace nebula {
 
 TEST(Parser, Go) {
+    {
+        GQLParser parser;
+        std::string query = "GO 0 STEPS FROM 1 OVER friend";
+        auto result = parser.parse(query);
+        ASSERT_TRUE(result.ok()) << result.status();
+    }
+    {
+        GQLParser parser;
+        std::string query = "GO -1 STEPS FROM 1 OVER friend";
+        auto result = parser.parse(query);
+        ASSERT_FALSE(result.ok()) << result.status();
+    }
     {
         GQLParser parser;
         std::string query = "GO FROM 1 OVER friend";