Fix parameter detection when using GroupBy method for Linq provider

src/NHibernate.Test/Async/Linq/ByMethod/GroupByHavingTests.cs

@@ -10,6 +10,7 @@
 
 using System;
 using System.Linq;
+using NHibernate.DomainModel.Northwind.Entities;
 using NUnit.Framework;
 using NHibernate.Linq;
 
@@ -147,5 +148,45 @@ public async Task SingleKeyGroupAndCountWithHavingClauseAsync()
 			var hornRow = orderCounts.Single(row => row.CompanyName == "Around the Horn");
 			Assert.That(hornRow.OrderCount, Is.EqualTo(13));
 		}
+
+		[Test]
+		public async Task HavingWithStringEnumParameterAsync()
+		{
+			await (db.Users
+			  .GroupBy(p => p.Enum1)
+			  .Where(g => g.Key == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new StringEnumGroup {Enum = p.Enum1})
+			  .Where(g => g.Key.Enum == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new[] {p.Enum1})
+			  .Where(g => g.Key[0] == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new {p.Enum1})
+			  .Where(g => g.Key.Enum1 == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new {Test = new {Test2 = p.Enum1}})
+			  .Where(g => g.Key.Test.Test2 == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new {Test = new[] {p.Enum1}})
+			  .Where(g => g.Key.Test[0] == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToListAsync());
+		}
+
+		private class StringEnumGroup
+		{
+			public EnumStoredAsString Enum { get; set; }
+		}
 	}
 }

src/NHibernate.Test/Async/Linq/ByMethod/GroupByTests.cs

@@ -382,6 +382,40 @@ public async Task GroupByAndAnyAsync()
 			Assert.That(namesAreNotEmpty, Is.True);
 		}
 
+		[Test]
+		public async Task GroupByWithStringEnumParameterAsync()
+		{
+			await (db.Users
+			  .GroupBy(p => p.Enum1)
+			  .Select(g => g.Key == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new StringEnumGroup {Enum = p.Enum1})
+			  .Select(g => g.Key.Enum == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new[] {p.Enum1})
+			  .Select(g => g.Key[0] == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new {p.Enum1})
+			  .Select(g => g.Key.Enum1 == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new {Test = new {Test2 = p.Enum1}})
+			  .Select(g => g.Key.Test.Test2 == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToListAsync());
+			await (db.Users
+			  .GroupBy(p => new {Test = new[] {p.Enum1}})
+			  .Select(g => g.Key.Test[0] == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToListAsync());
+		}
+
+		private class StringEnumGroup
+		{
+			public EnumStoredAsString Enum { get; set; }
+		}
+
 		[Test]
 		public async Task SelectFirstElementFromProductsGroupedByUnitPriceAsync()
 		{

src/NHibernate.Test/Linq/ByMethod/GroupByHavingTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Linq;
+using NHibernate.DomainModel.Northwind.Entities;
 using NUnit.Framework;
 
 namespace NHibernate.Test.Linq.ByMethod
@@ -135,5 +136,45 @@ public void SingleKeyGroupAndCountWithHavingClause()
 			var hornRow = orderCounts.Single(row => row.CompanyName == "Around the Horn");
 			Assert.That(hornRow.OrderCount, Is.EqualTo(13));
 		}
+
+		[Test]
+		public void HavingWithStringEnumParameter()
+		{
+			db.Users
+			  .GroupBy(p => p.Enum1)
+			  .Where(g => g.Key == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new StringEnumGroup {Enum = p.Enum1})
+			  .Where(g => g.Key.Enum == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new[] {p.Enum1})
+			  .Where(g => g.Key[0] == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new {p.Enum1})
+			  .Where(g => g.Key.Enum1 == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new {Test = new {Test2 = p.Enum1}})
+			  .Where(g => g.Key.Test.Test2 == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new {Test = new[] {p.Enum1}})
+			  .Where(g => g.Key.Test[0] == EnumStoredAsString.Large)
+			  .Select(g => g.Count())
+			  .ToList();
+		}
+
+		private class StringEnumGroup
+		{
+			public EnumStoredAsString Enum { get; set; }
+		}
 	}
 }

src/NHibernate.Test/Linq/ByMethod/GroupByTests.cs

@@ -371,6 +371,40 @@ public void GroupByAndAny()
 			Assert.That(namesAreNotEmpty, Is.True);
 		}
 
+		[Test]
+		public void GroupByWithStringEnumParameter()
+		{
+			db.Users
+			  .GroupBy(p => p.Enum1)
+			  .Select(g => g.Key == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new StringEnumGroup {Enum = p.Enum1})
+			  .Select(g => g.Key.Enum == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new[] {p.Enum1})
+			  .Select(g => g.Key[0] == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new {p.Enum1})
+			  .Select(g => g.Key.Enum1 == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new {Test = new {Test2 = p.Enum1}})
+			  .Select(g => g.Key.Test.Test2 == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToList();
+			db.Users
+			  .GroupBy(p => new {Test = new[] {p.Enum1}})
+			  .Select(g => g.Key.Test[0] == EnumStoredAsString.Large ? g.Sum(o => o.Id) : 0)
+			  .ToList();
+		}
+
+		private class StringEnumGroup
+		{
+			public EnumStoredAsString Enum { get; set; }
+		}
+
 		[Test]
 		public void SelectFirstElementFromProductsGroupedByUnitPrice()
 		{

src/NHibernate/Linq/ExpressionExtensions.cs

@@ -15,6 +15,23 @@ public static bool IsGroupingKey(this MemberExpression expression)
 					 expression.Member.DeclaringType.IsGenericType && expression.Member.DeclaringType.GetGenericTypeDefinition() == typeof(IGrouping<,>);
 		}
 
+		internal static bool TryGetGroupResultOperator(this MemberExpression keyExpression, out GroupResultOperator groupBy)
+		{
+			if (keyExpression.IsGroupingKey() &&
+				keyExpression.Expression is QuerySourceReferenceExpression querySource &&
+				querySource.ReferencedQuerySource is MainFromClause fromClause &&
+				fromClause.FromExpression is SubQueryExpression query)
+			{
+				groupBy = query.QueryModel.ResultOperators
+				               .OfType<GroupResultOperator>()
+				               .FirstOrDefault(o => o.KeySelector.Type == keyExpression.Type);
+				return groupBy != null;
+			}
+
+			groupBy = null;
+			return false;
+		}
+
 		public static bool IsGroupingKeyOf(this MemberExpression expression,GroupResultOperator groupBy)
 		{
 			if (!expression.IsGroupingKey())

src/NHibernate/Linq/Visitors/ParameterTypeLocator.cs

@@ -343,6 +343,7 @@ private void VisitAssign(Expression leftNode, Expression rightNode)
 			private void AddRelatedExpression(Expression node, Expression left, Expression right)
 			{
 				if (left.NodeType == ExpressionType.MemberAccess ||
+					left.NodeType == ExpressionType.ArrayIndex || // e.g. group.Key[0] == variable
 					IsDynamicMember(left) ||
 					left is QuerySourceReferenceExpression)
 				{

src/NHibernate/Util/ExpressionsHelper.cs

@@ -17,7 +17,7 @@
 using Remotion.Linq.Clauses;
 using Remotion.Linq.Clauses.Expressions;
 using Remotion.Linq.Clauses.ResultOperators;
-using Remotion.Linq.Parsing;
+using TransparentIdentifierRemovingExpressionVisitor = NHibernate.Linq.Visitors.TransparentIdentifierRemovingExpressionVisitor;
 
 namespace NHibernate.Util
 {
@@ -594,6 +594,43 @@ private static IType GetType(
 				: TypeFactory.GetDefaultTypeFor(member.ConvertType); // (long)q.OneToMany[0]
 		}
 
+		private class GroupingKeyFlattener : NhExpressionVisitor
+		{
+			private bool _flattened;
+
+			public static Expression FlattenGroupingKey(Expression expression)
+			{
+				var visitor = new GroupingKeyFlattener();
+				expression = visitor.Visit(expression);
+				if (visitor._flattened)
+				{
+					expression = TransparentIdentifierRemovingExpressionVisitor.ReplaceTransparentIdentifiers(expression);
+					// When the grouping key is an array we have to unwrap it (e.g. group.Key[0] == variable)
+					if (expression.NodeType == ExpressionType.ArrayIndex &&
+					    expression is BinaryExpression binaryExpression &&
+					    binaryExpression.Left is NewArrayExpression newArray &&
+					    binaryExpression.Right is ConstantExpression indexExpression &&
+					    indexExpression.Value is int index)
+					{
+						return newArray.Expressions[index];
+					}
+				}
+
+				return expression;
+			}
+
+			protected override Expression VisitMember(MemberExpression node)
+			{
+				if (node.TryGetGroupResultOperator(out var groupBy))
+				{
+					_flattened = true;
+					return groupBy.KeySelector;
+				}
+
+				return base.VisitMember(node);
+			}
+		}
+
 		private class MemberMetadataExtractor : NhExpressionVisitor
 		{
 			private readonly List<MemberMetadataResult> _childrenResults = new List<MemberMetadataResult>();
@@ -639,6 +676,8 @@ private static bool TryGetAllMemberMetadata(
 				bool hasIndexer,
 				out MemberMetadataResult results)
 			{
+				expression = GroupingKeyFlattener.FlattenGroupingKey(expression);
+
 				var extractor = new MemberMetadataExtractor(memberPaths, convertType, hasIndexer);
 				extractor.Accept(expression);
 				results = extractor._entityName != null || extractor._childrenResults.Count > 0