TINKERPOP-3147 Prevent aggregate step from having multiple by modulators

CHANGELOG.asciidoc

@@ -24,7 +24,7 @@ image::https://raw.githubusercontent.com/apache/tinkerpop/master/docs/static/ima
 === TinkerPop 3.8.0 (Release Date: NOT OFFICIALLY RELEASED YET)
 
 This release also includes changes from <<release-3-7-XXX, 3.7.XXX>>.
-
+* Changed aggregate step to not allow multiple by modulators.
 * Modified `TraversalStrategy` construction in Javascript where configurations are now supplied as a `Map` of options.
 * Fixed bug in GraphSON v2 and v3 where full round trip of `TraversalStrategy` implementations was failing.
 * Added missing strategies to the `TraversalStrategies` global cache as well as `CoreImports` in `gremlin-groovy`.

gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/AggregateGlobalStep.java

@@ -69,6 +69,8 @@ public String toString() {
 
     @Override
     public void modulateBy(final Traversal.Admin<?, ?> aggregateTraversal) {
+        if (this.aggregateTraversal != null)
+            throw new IllegalStateException("Aggregate step can only have one by modulator");
         this.aggregateTraversal = this.integrateChild(aggregateTraversal);
     }
 

gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/sideEffect/AggregateLocalStep.java

@@ -87,6 +87,8 @@ public List<Traversal.Admin<S, Object>> getLocalChildren() {
 
     @Override
     public void modulateBy(final Traversal.Admin<?, ?> storeTraversal) {
+        if (this.storeTraversal != null)
+            throw new IllegalStateException("Aggregate step can only have one by modulator");
         this.storeTraversal = this.integrateChild(storeTraversal);
     }
 

gremlin-dotnet/test/Gremlin.Net.IntegrationTest/Gherkin/Gremlin.cs

@@ -343,6 +343,8 @@ private static IDictionary<string, List<Func<GraphTraversalSource, IDictionary<s
                {"g_V_mapXin_hasIdX1XX_limitX2X_valuesXnameX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Map<object>(__.In().HasId(p["vid1"])).Limit<object>(2).Values<object>("name")}}, 
                {"g_V_rangeX2_1X", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Range<object>(2, 1)}}, 
                {"g_V_rangeX3_2X", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Range<object>(3, 2)}}, 
+               {"g_V_aggregateXxX_byXnameX_byXageX_capXxX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Aggregate("x").By("name").By("age").Cap<object>("x")}}, 
+               {"g_V_aggregateXScope_local_xX_byXnameX_byXageX_capXxX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Aggregate(Scope.Local, "x").By("name").By("age").Cap<object>("x")}}, 
                {"g_E_sampleX1X", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.E().Sample(1)}}, 
                {"g_E_sampleX2X_byXweightX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.E().Sample(2).By("weight")}}, 
                {"g_V_localXoutE_sampleX1X_byXweightXX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Local<object>(__.OutE().Sample(1).By("weight"))}}, 

gremlin-go/driver/cucumber/gremlin.go

@@ -312,6 +312,8 @@ var translationMap = map[string][]func(g *gremlingo.GraphTraversalSource, p map[
     "g_V_mapXin_hasIdX1XX_limitX2X_valuesXnameX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Map(gremlingo.T__.In().HasId(p["vid1"])).Limit(2).Values("name")}}, 
     "g_V_rangeX2_1X": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Range(2, 1)}}, 
     "g_V_rangeX3_2X": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Range(3, 2)}}, 
+    "g_V_aggregateXxX_byXnameX_byXageX_capXxX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Aggregate("x").By("name").By("age").Cap("x")}}, 
+    "g_V_aggregateXScope_local_xX_byXnameX_byXageX_capXxX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Aggregate(gremlingo.Scope.Local, "x").By("name").By("age").Cap("x")}}, 
     "g_E_sampleX1X": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.E().Sample(1)}}, 
     "g_E_sampleX2X_byXweightX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.E().Sample(2).By("weight")}}, 
     "g_V_localXoutE_sampleX1X_byXweightXX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Local(gremlingo.T__.OutE().Sample(1).By("weight"))}}, 

gremlin-python/src/main/python/radish/gremlin.py

@@ -315,6 +315,8 @@
     'g_V_mapXin_hasIdX1XX_limitX2X_valuesXnameX': [(lambda g, vid1=None:g.V().map(__.in_().has_id(vid1)).limit(2).values('name'))], 
     'g_V_rangeX2_1X': [(lambda g:g.V().range_(2, 1))], 
     'g_V_rangeX3_2X': [(lambda g:g.V().range_(3, 2))], 
+    'g_V_aggregateXxX_byXnameX_byXageX_capXxX': [(lambda g:g.V().aggregate('x').by('name').by('age').cap('x'))], 
+    'g_V_aggregateXScope_local_xX_byXnameX_byXageX_capXxX': [(lambda g:g.V().aggregate(Scope.local, 'x').by('name').by('age').cap('x'))], 
     'g_E_sampleX1X': [(lambda g:g.E().sample(1))], 
     'g_E_sampleX2X_byXweightX': [(lambda g:g.E().sample(2).by('weight'))], 
     'g_V_localXoutE_sampleX1X_byXweightXX': [(lambda g:g.V().local(__.out_e().sample(1).by('weight')))], 

gremlin-test/src/main/resources/org/apache/tinkerpop/gremlin/test/features/filter/Sample.feature

@@ -18,6 +18,24 @@
 @StepClassFilter @StepSample
 Feature: Step - sample()
 
+  Scenario: g_V_aggregateXxX_byXnameX_byXageX_capXxX
+    Given the modern graph
+    And the traversal of
+      """
+      g.V().aggregate("x").by("name").by("age").cap("x")
+      """
+    When iterated to list
+    Then the traversal will raise an error with message containing text of "Aggregate step can only have one by modulator"
+
+  Scenario: g_V_aggregateXScope_local_xX_byXnameX_byXageX_capXxX
+    Given the modern graph
+    And the traversal of
+      """
+      g.V().aggregate(Scope.local, "x").by("name").by("age").cap("x")
+      """
+    When iterated to list
+    Then the traversal will raise an error with message containing text of "Aggregate step can only have one by modulator"
+
   Scenario: g_E_sampleX1X
     Given the modern graph
     And the traversal of