Force left join for comparisons with nullable entities (nhibernate#3270)

Fixes nhibernate#3269

Author: bahusoid

src/NHibernate.Test/Async/Hql/EntityJoinHqlTest.cs

@@ -358,6 +358,15 @@ from x2 in session.Query<NullableOwner>()
 				//GH-2988
 				var withNullOrValidList = await (session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == validManyToOne.Id || x.ManyToOne == null).ToListAsync());
 				var withNullOrValidList2 = await (session.Query<NullableOwner>().Where(x =>  x.ManyToOne == null || x.ManyToOne.Id == validManyToOne.Id).ToListAsync());
+				//GH-3269
+				var invalidId = Guid.NewGuid();
+				var withInvalidOrValid = await (session.Query<NullableOwner>().Where(x => x.OneToOne.Id == invalidId || x.ManyToOne.Id == validManyToOne.Id).ToListAsync());
+				var withInvalidOrNull = await (session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == invalidId || x.OneToOne == null).ToListAsync());
+				var withInvalidOrNotNull = await (session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == invalidId || x.OneToOne != null).ToListAsync());
+
+				Assert.That(withInvalidOrValid.Count, Is.EqualTo(1));
+				Assert.That(withInvalidOrNull.Count, Is.EqualTo(2));
+				Assert.That(withInvalidOrNotNull.Count, Is.EqualTo(0));
 
 				//GH-3185
 				var mixImplicitAndLeftJoinList = await (session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == validManyToOne.Id && x.OneToOne == null).ToListAsync());

src/NHibernate.Test/Hql/EntityJoinHqlTest.cs

@@ -346,6 +346,15 @@ from x2 in session.Query<NullableOwner>()
 				//GH-2988
 				var withNullOrValidList = session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == validManyToOne.Id || x.ManyToOne == null).ToList();
 				var withNullOrValidList2 = session.Query<NullableOwner>().Where(x =>  x.ManyToOne == null || x.ManyToOne.Id == validManyToOne.Id).ToList();
+				//GH-3269
+				var invalidId = Guid.NewGuid();
+				var withInvalidOrValid = session.Query<NullableOwner>().Where(x => x.OneToOne.Id == invalidId || x.ManyToOne.Id == validManyToOne.Id).ToList();
+				var withInvalidOrNull = session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == invalidId || x.OneToOne == null).ToList();
+				var withInvalidOrNotNull = session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == invalidId || x.OneToOne != null).ToList();
+
+				Assert.That(withInvalidOrValid.Count, Is.EqualTo(1));
+				Assert.That(withInvalidOrNull.Count, Is.EqualTo(2));
+				Assert.That(withInvalidOrNotNull.Count, Is.EqualTo(0));
 
 				//GH-3185
 				var mixImplicitAndLeftJoinList = session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == validManyToOne.Id && x.OneToOne == null).ToList();

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

@@ -42,7 +42,6 @@ public partial class HqlSqlWalker
 		private SelectClause _selectClause;
 		private readonly AliasGenerator _aliasGenerator = new AliasGenerator();
 		private readonly ASTPrinter _printer = new ASTPrinter();
-		private bool _isNullComparison;
 
 		//
 		//Maps each top-level result variable to its SelectExpression;
@@ -1209,8 +1208,6 @@ public IASTFactory ASTFactory
 			}
 		}
 
-		internal bool IsNullComparison => _isNullComparison;
-
 		public void AddQuerySpaces(string[] spaces)
 		{
 			for (int i = 0; i < spaces.Length; i++)

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

@@ -380,7 +380,7 @@ comparisonExpr
 	| ^(NOT_BETWEEN exprOrSubquery exprOrSubquery exprOrSubquery)
 	| ^(IN exprOrSubquery inRhs )
 	| ^(NOT_IN exprOrSubquery inRhs )
-	| ^(IS_NULL { _isNullComparison = true; } exprOrSubquery { _isNullComparison = false; })
+	| ^(IS_NULL exprOrSubquery)
 	| ^(IS_NOT_NULL exprOrSubquery)
 //	| ^(IS_TRUE expr)
 //	| ^(IS_FALSE expr)

src/NHibernate/Hql/Ast/ANTLR/Tree/DotNode.cs

@@ -417,8 +417,7 @@ private void DereferenceEntity(EntityType entityType, bool implicitJoin, string
 
 			if ( joinIsNeeded )
 			{
-				var forceLeftJoin = comparisonWithNullableEntity && Walker.IsNullComparison;
-				DereferenceEntityJoin(classAlias, entityType, implicitJoin, parent, forceLeftJoin);
+				DereferenceEntityJoin(classAlias, entityType, implicitJoin, parent, comparisonWithNullableEntity);
 				if (comparisonWithNullableEntity)
 				{
 					_columns = FromElement.GetIdentityColumns();