Fix build path. (vesoft-inc#4091)

Co-authored-by: jie.wang <38901892+jievince@users.noreply.github.com>
Co-authored-by: Sophie <84560950+Sophie-Xie@users.noreply.github.com>

src/common/expression/PathBuildExpression.cpp

@@ -39,10 +39,14 @@ bool PathBuildExpression::buildPath(const Value& value, Path& path) const {
   switch (value.type()) {
     case Value::Type::EDGE: {
       Step step;
+      bool result = true;
       if (!path.steps.empty()) {
-        getEdge(value, path.steps.back().dst.vid, step);
+        result = getEdge(value, path.steps.back().dst.vid, step);
       } else {
-        getEdge(value, path.src.vid, step);
+        result = getEdge(value, path.src.vid, step);
+      }
+      if (!result) {
+        return result;
       }
       path.steps.emplace_back(std::move(step));
       break;
@@ -68,9 +72,20 @@ bool PathBuildExpression::buildPath(const Value& value, Path& path) const {
       break;
     }
     case Value::Type::LIST: {
+      bool result = true;
       for (const auto& val : value.getList().values) {
         if (!buildPath(val, path)) {
-          return false;
+          result = false;
+          break;
+        }
+      }
+      if (!result) {
+        for (std::vector<Value>::const_reverse_iterator it = value.getList().values.rbegin();
+             it != value.getList().values.rend();
+             ++it) {
+          if (!buildPath(*it, path)) {
+            return false;
+          }
         }
       }
       break;
@@ -110,12 +125,14 @@ bool PathBuildExpression::getEdge(const Value& value, const Value& lastStepVid,
     step.ranking = edge.ranking;
     step.props = edge.props;
     step.dst.vid = edge.dst;
-  } else {
+  } else if (lastStepVid == edge.dst) {
     step.type = -edge.type;
     step.name = edge.name;
     step.ranking = edge.ranking;
     step.props = edge.props;
     step.dst.vid = edge.src;
+  } else {
+    return false;
   }
   return true;
 }

tests/tck/features/bugfix/BuildPathMistake.feature

@@ -0,0 +1,18 @@
+# Copyright (c) 2022 vesoft inc. All rights reserved.
+#
+# This source code is licensed under Apache 2.0 License.
+Feature: Test crash when null path expression
+
+  Background:
+    Given a graph with space named "nba"
+
+  Scenario: Null path expression in multiple patterns
+    When executing query:
+      """
+      MATCH p = ()-[:like*2]->(v:player) WHERE id(v) == 'Grant Hill' RETURN p
+      """
+    Then the result should be, in any order, with relax comparison:
+      | p                                                                                                                                                                                                                           |
+      | <("Yao Ming" :player{age: 38, name: "Yao Ming"})-[:like@0 {likeness: 90}]->("Tracy McGrady" :player{age: 39, name: "Tracy McGrady"})-[:like@0 {likeness: 90}]->("Grant Hill" :player{age: 46, name: "Grant Hill"})>         |
+      | <("Grant Hill" :player{age: 46, name: "Grant Hill"})<-[:like@0 {likeness: 90}]-("Tracy McGrady" :player{age: 39, name: "Tracy McGrady"})<-[:like@0 {likeness: 90}]-("Grant Hill" :player{age: 46, name: "Grant Hill"})>     |
+      | <("Vince Carter" :player{age: 42, name: "Vince Carter"})-[:like@0 {likeness: 90}]->("Tracy McGrady" :player{age: 39, name: "Tracy McGrady"})-[:like@0 {likeness: 90}]->("Grant Hill" :player{age: 46, name: "Grant Hill"})> |