[TINKERPOP-2972] ProjectStep does not allow keys specified in a query…

… to be duplicate (#2217)

Co-authored-by: Yang Xia <[email protected]>

CHANGELOG.asciidoc

@@ -31,6 +31,7 @@ This release also includes changes from <<release-3-5-8, 3.5.8>>.
 * Fixed a bug in `StarGraph` where `EdgeFilter` did not remove associated Edge Properties.
 * Added translator to the Go GLV.
 * Fixed bug with filtering for `group()` when the side-effect label was defined for it.
+* ProjectStep now throws exception when a duplicate key is provided in a query.
 * Fixed bug in `DotNetTranslator` where `PartitionStrategy` usage was not translating properly when specifying the `readPartitions`.
 * Fixed bug in `PythonTranslator` where `Set` syntax was not being generated properly.
 * Fixed bug in configuration object given to `PartitionStrategy` for Go that prevented `readPartitions` from behing set properly.

gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/ProjectStep.java

@@ -29,10 +29,12 @@
 import org.apache.tinkerpop.gremlin.structure.util.StringFactory;
 
 import java.util.Arrays;
+import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 /**
  * @author Marko A. Rodriguez (http://markorodriguez.com)
@@ -48,6 +50,11 @@ public ProjectStep(final Traversal.Admin traversal, final String... projectKeys)
 
     public ProjectStep(final Traversal.Admin traversal, final TraversalRing<S, E> traversalRing, final String... projectKeys) {
         super(traversal);
+
+        if (Arrays.stream(projectKeys).collect(Collectors.toSet()).size() != projectKeys.length) {
+            throw new IllegalArgumentException("keys must be unique in ProjectStep");
+        }
+
         this.projectKeys = Arrays.asList(projectKeys);
         this.traversalRing = traversalRing;
     }

gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/ProjectStepTest.java

@@ -22,10 +22,16 @@
 import org.apache.tinkerpop.gremlin.process.traversal.Traversal;
 import org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.__;
 import org.apache.tinkerpop.gremlin.process.traversal.step.StepTest;
+import org.junit.Test;
 
 import java.util.Arrays;
 import java.util.List;
 
+import static org.hamcrest.CoreMatchers.instanceOf;
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.Assert.fail;
+
 /**
  * @author Marko A. Rodriguez (http://markorodriguez.com)
  */
@@ -44,4 +50,15 @@ protected List<Traversal> getTraversals() {
                 __.project("y").by("name")
         );
     }
+
+    @Test
+    public void shouldThrowWhenDuplicateKeySupplied() {
+        try {
+            __.project("x", "x");
+            fail("Should throw an exception.");
+        } catch (final Exception re) {
+            assertThat(re, instanceOf(IllegalArgumentException.class));
+            assertThat(re.getMessage(), is("keys must be unique in ProjectStep"));
+        }
+    }
 }