Fix NRE with reused fetch and collection join (nhibernate#3314)

Fixes nhibernate#3288

Author: bahusoid

src/NHibernate.Test/Async/NHSpecificTest/GH3288/FetchAndCollectionJoinFixture.cs

@@ -0,0 +1,58 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by AsyncGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+
+using System.Linq;
+using NHibernate.Linq;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH3288
+{
+	using System.Threading.Tasks;
+	[TestFixture]
+	public class FetchAndCollectionJoinFixtureAsync : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+			var middleEntity = new MiddleEntity();
+			middleEntity.Components.Add(new Component { MiddleEntity = middleEntity, Value = 1 });
+			var te = new TopEntity
+			{
+				MiddleEntity = middleEntity
+			};
+			session.Save(middleEntity);
+			session.Save(te);
+
+			transaction.Commit();
+		}
+
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+			session.Delete("from System.Object");
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public async Task ReuseEntityJoinWithCollectionJoinAsync()
+		{
+			using var session = OpenSession();
+
+			var entities = await (session.Query<TopEntity>()
+				.Fetch(e => e.MiddleEntity)
+				.Where(e => e.MiddleEntity.Components.Any(e => e.Value != 0))
+				.ToListAsync());
+			Assert.That(entities.Count, Is.EqualTo(1));
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3288/Entity.cs

@@ -0,0 +1,31 @@
+using System.Collections.Generic;
+
+namespace NHibernate.Test.NHSpecificTest.GH3288
+{
+	class TopEntity
+	{
+		public virtual int Id { get; set; }
+		public virtual MiddleEntity MiddleEntity { get; set; }
+	}
+	class MiddleEntity
+	{
+		public virtual int Id { get; set; }
+		public virtual ISet<Component> Components { get; set; } = new HashSet<Component>();
+	}
+
+	class Component
+	{
+		public virtual MiddleEntity MiddleEntity { get; set; }
+		public virtual int Value { get; set; }
+
+		public override bool Equals(object obj)
+		{
+			return (obj as Component)?.MiddleEntity.Id == MiddleEntity.Id;
+		}
+
+		public override int GetHashCode()
+		{
+			return MiddleEntity.Id.GetHashCode();
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3288/FetchAndCollectionJoinFixture.cs

@@ -0,0 +1,47 @@
+using System.Linq;
+using NHibernate.Linq;
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH3288
+{
+	[TestFixture]
+	public class FetchAndCollectionJoinFixture : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+			var middleEntity = new MiddleEntity();
+			middleEntity.Components.Add(new Component { MiddleEntity = middleEntity, Value = 1 });
+			var te = new TopEntity
+			{
+				MiddleEntity = middleEntity
+			};
+			session.Save(middleEntity);
+			session.Save(te);
+
+			transaction.Commit();
+		}
+
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+			session.Delete("from System.Object");
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public void ReuseEntityJoinWithCollectionJoin()
+		{
+			using var session = OpenSession();
+
+			var entities = session.Query<TopEntity>()
+				.Fetch(e => e.MiddleEntity)
+				.Where(e => e.MiddleEntity.Components.Any(e => e.Value != 0))
+				.ToList();
+			Assert.That(entities.Count, Is.EqualTo(1));
+		}
+	}
+}

src/NHibernate.Test/NHSpecificTest/GH3288/Mappings.hbm.xml

@@ -0,0 +1,26 @@
+<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
+                   namespace="NHibernate.Test.NHSpecificTest.GH3288"
+                   assembly="NHibernate.Test">
+  <class name="TopEntity" table="`TopEntity`">
+    <id name="Id" >
+      <generator class="identity" />
+    </id>
+    <many-to-one class="MiddleEntity" name="MiddleEntity">
+      <column name="MiddleEntity_id" />
+    </many-to-one>
+  </class>
+<class name="MiddleEntity" table="`MiddleEntity`">
+  <id name="Id" >
+    <generator class="identity" />
+  </id>
+  <set cascade="all" name="Components" table="BottomEntity">
+    <key not-null="true">
+      <column name="MiddleEntity_id" />
+    </key>
+    <composite-element class="Component">
+      <parent name="MiddleEntity" />
+      <property name="Value" column="`Value`" />
+    </composite-element>
+  </set>
+</class>
+</hibernate-mapping>

src/NHibernate/Hql/Ast/ANTLR/HqlSqlWalker.cs

@@ -527,7 +527,7 @@ internal string GetEntitySuffix(FromElement fromElement)
 
 		internal string GetCollectionSuffix(FromElement fromElement)
 		{
-			if (!fromElement.CollectionJoin && fromElement.QueryableCollection == null)
+			if (fromElement.QueryableCollection == null)
 			{
 				return null;
 			}