Fix #3014: Missing type information in lambda expressions.

ICSharpCode.Decompiler.Tests/TestCases/Pretty/ExpressionTrees.cs

@@ -223,15 +223,15 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		private dynamic ViewBag;
 
 		public static readonly object[] SupportedMethods = new object[2] {
-			ToCode(null, () => ((IQueryable<object>)null).Aggregate((object o1, object o2) => null)),
+			ToCode(null, () => ((IQueryable<object>)null).Aggregate((object o1, object o2) => (object)null)),
-			ToCode(null, () => ((IEnumerable<object>)null).Aggregate((object o1, object o2) => null))
+			ToCode(null, () => ((IEnumerable<object>)null).Aggregate((object o1, object o2) => (object)null))
 		};
 
 		public static readonly object[] SupportedMethods2 = new object[4] {
-			ToCode(null, () => ((IQueryable<object>)null).Aggregate(null, (object o1, object o2) => null)),
+			ToCode(null, () => ((IQueryable<object>)null).Aggregate(null, (object o1, object o2) => (object)null)),
-			ToCode(null, () => ((IQueryable<object>)null).Aggregate((object)null, (Expression<Func<object, object, object>>)((object o1, object o2) => null), (Expression<Func<object, object>>)((object o) => null))),
+			ToCode(null, () => ((IQueryable<object>)null).Aggregate(null, (object o1, object o2) => (object)null, (object o) => (object)null)),
-			ToCode(null, () => ((IEnumerable<object>)null).Aggregate(null, (object o1, object o2) => null)),
+			ToCode(null, () => ((IEnumerable<object>)null).Aggregate(null, (object o1, object o2) => (object)null)),
-			ToCode(null, () => ((IEnumerable<object>)null).Aggregate((object)null, (Func<object, object, object>)((object o1, object o2) => null), (Func<object, object>)((object o) => null)))
+			ToCode(null, () => ((IEnumerable<object>)null).Aggregate(null, (object o1, object o2) => (object)null, (object o) => (object)null))
 		};
 
 		public static void TestCall(object a)

ICSharpCode.Decompiler.Tests/TestCases/Pretty/FixProxyCalls.cs

@@ -120,7 +120,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.ILPretty
 		public Action<object> M(object state)
 		{
 			return delegate (object x) {
-				base.BaseCall(x, state, (Func<object>)(() => null));
+				base.BaseCall(x, state, () => (object)null);
 			};
 		}
 	}

ICSharpCode.Decompiler.Tests/TestCases/Pretty/TupleTests.cs

@@ -77,7 +77,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		public int AccessPartiallyNamed => PartiallyNamed.a + PartiallyNamed.Item3;
 
 		public ValueTuple<int> NewTuple1 => new ValueTuple<int>(1);
-		public (int a, int b) NewTuple2 => (1, 2);
+		public (int a, int b) NewTuple2 => (a: 1, b: 2);
 		public object BoxedTuple10 => (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
 
 		public (uint, int) SwapUnnamed => (Unnamed2.Item2, Unnamed2.Item1);
@@ -115,7 +115,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 
 		public void NamedTupleOut(out (int A, string B, Action C, dynamic D) tuple)
 		{
-			tuple = (42, "Hello", Console.WriteLine, null);
+			tuple = (A: 42, B: "Hello", C: Console.WriteLine, D: null);
 		}
 
 		public void NamedTupleIn(in (int A, string B, Action C, dynamic D) tuple)
@@ -141,6 +141,27 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Console.WriteLine(TupleDict.Values.ToList().First().d);
 		}
 
+		private static (string, string) Issue3014a(string[] args)
+		{
+			return (from v in args
+					select (Name: v, Value: v) into kvp
+					orderby kvp.Name
+					select kvp).First();
+		}
+
+		private static (string, string) Issue3014b(string[] args)
+		{
+			return (from v in args
+					select ((string Name, string Value))GetTuple() into kvp
+					orderby kvp.Name
+					select kvp).First();
+
+			(string, string) GetTuple()
+			{
+				return (args[0], args[1]);
+			}
+		}
+
 		public void Issue1174()
 		{
 			Console.WriteLine((1, 2, 3).GetHashCode());

ICSharpCode.Decompiler/CSharp/CallBuilder.cs

@@ -189,7 +189,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			this.typeSystem = typeSystem;
 		}
 
-		public TranslatedExpression Build(CallInstruction inst)
+		public TranslatedExpression Build(CallInstruction inst, IType typeHint = null)
 		{
 			if (inst is NewObj newobj && IL.Transforms.DelegateConstruction.MatchDelegateConstruction(newobj, out _, out _, out _))
 			{
@@ -198,20 +198,29 @@ namespace ICSharpCode.Decompiler.CSharp
 			if (settings.TupleTypes && TupleTransform.MatchTupleConstruction(inst as NewObj, out var tupleElements) && tupleElements.Length >= 2)
 			{
 				var elementTypes = TupleType.GetTupleElementTypes(inst.Method.DeclaringType);
-				Debug.Assert(!elementTypes.IsDefault, "MatchTupleConstruction should not success unless we got a valid tuple type.");
+				var elementNames = typeHint is TupleType tt ? tt.ElementNames : default;
+				Debug.Assert(!elementTypes.IsDefault, "MatchTupleConstruction should not succeed unless we got a valid tuple type.");
 				Debug.Assert(elementTypes.Length == tupleElements.Length);
 				var tuple = new TupleExpression();
 				var elementRRs = new List<ResolveResult>();
-				foreach (var (element, elementType) in tupleElements.Zip(elementTypes))
+				foreach (var (index, element, elementType) in tupleElements.ZipWithIndex(elementTypes))
 				{
 					var translatedElement = expressionBuilder.Translate(element, elementType)
 						.ConvertTo(elementType, expressionBuilder, allowImplicitConversion: true);
-					tuple.Elements.Add(translatedElement.Expression);
+					if (elementNames.IsDefaultOrEmpty || elementNames.ElementAtOrDefault(index) is not string { Length: > 0 } name)
+					{
+						tuple.Elements.Add(translatedElement.Expression);
+					}
+					else
+					{
+						tuple.Elements.Add(new NamedArgumentExpression(name, translatedElement.Expression));
+					}
 					elementRRs.Add(translatedElement.ResolveResult);
 				}
 				return tuple.WithRR(new TupleResolveResult(
 					expressionBuilder.compilation,
 					elementRRs.ToImmutableArray(),
+					elementNames,
 					valueTupleAssembly: inst.Method.DeclaringType.GetDefinition()?.ParentModule
 				)).WithILInstruction(inst);
 			}

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -22,7 +22,6 @@ using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Linq;
 using System.Reflection.Metadata;
-using System.Runtime.CompilerServices;
 using System.Threading;
 
 using ICSharpCode.Decompiler.CSharp.Resolver;
@@ -438,7 +437,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					return TranslateStackAllocInitializer(b, type.TypeArguments[0]);
 				}
 			}
-			return new CallBuilder(this, typeSystem, settings).Build(inst);
+			return new CallBuilder(this, typeSystem, settings).Build(inst, context.TypeHint);
 		}
 
 		protected internal override TranslatedExpression VisitLdVirtDelegate(LdVirtDelegate inst, TranslationContext context)

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -395,8 +395,14 @@ namespace ICSharpCode.Decompiler.CSharp
 					return new YieldBreakStatement().WithILInstruction(inst);
 				else if (!inst.Value.MatchNop())
 				{
+					bool isLambdaOrExprTree = currentFunction.Kind is ILFunctionKind.ExpressionTree or ILFunctionKind.Delegate;
 					var expr = exprBuilder.Translate(inst.Value, typeHint: currentResultType)
 						.ConvertTo(currentResultType, exprBuilder, allowImplicitConversion: true);
+					if (isLambdaOrExprTree && IsPossibleLossOfTypeInformation(expr.Type, currentResultType))
+					{
+						expr = new CastExpression(exprBuilder.ConvertType(currentResultType), expr)
+							.WithRR(new ConversionResolveResult(currentResultType, expr.ResolveResult, Conversion.IdentityConversion)).WithoutILInstruction();
+					}
 					return new ReturnStatement(expr).WithILInstruction(inst);
 				}
 				else
@@ -419,6 +425,19 @@ namespace ICSharpCode.Decompiler.CSharp
 			return new GotoStatement(label).WithILInstruction(inst);
 		}
 
+		private bool IsPossibleLossOfTypeInformation(IType givenType, IType expectedType)
+		{
+			if (NormalizeTypeVisitor.IgnoreNullability.EquivalentTypes(givenType, expectedType))
+				return false;
+			if (expectedType is TupleType { ElementNames.IsEmpty: false })
+				return true;
+			if (expectedType == SpecialType.Dynamic)
+				return true;
+			if (givenType == SpecialType.NullType)
+				return true;
+			return false;
+		}
+
 		protected internal override TranslatedStatement VisitThrow(Throw inst)
 		{
 			return new ThrowStatement(exprBuilder.Translate(inst.Argument)).WithILInstruction(inst);

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -272,11 +272,20 @@ namespace ICSharpCode.Decompiler.CSharp
 				// Conversion of a tuple literal: convert element-wise
 				var newTupleExpr = new TupleExpression();
 				var newElementRRs = new List<ResolveResult>();
-				foreach (var (elementExpr, elementTargetType) in tupleExpr.Elements.Zip(targetTupleType.ElementTypes))
+				// element names: discard existing names and use targetTupleType instead
+				var newElementNames = targetTupleType.ElementNames;
+				foreach (var (index, elementExpr, elementTargetType) in tupleExpr.Elements.ZipWithIndex(targetTupleType.ElementTypes))
 				{
-					var newElementExpr = new TranslatedExpression(elementExpr.Detach())
+					var newElementExpr = new TranslatedExpression((elementExpr is NamedArgumentExpression nae ? nae.Expression : elementExpr).Detach())
 						.ConvertTo(elementTargetType, expressionBuilder, checkForOverflow, allowImplicitConversion);
-					newTupleExpr.Elements.Add(newElementExpr.Expression);
+					if (newElementNames.IsDefaultOrEmpty || newElementNames.ElementAtOrDefault(index) is not string { Length: > 0 } name)
+					{
+						newTupleExpr.Elements.Add(newElementExpr.Expression);
+					}
+					else
+					{
+						newTupleExpr.Elements.Add(new NamedArgumentExpression(name, newElementExpr.Expression));
+					}
 					newElementRRs.Add(newElementExpr.ResolveResult);
 				}
 				return newTupleExpr.WithILInstruction(this.ILInstructions)

ICSharpCode.Decompiler/TypeSystem/NormalizeTypeVisitor.cs

@@ -50,6 +50,17 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			RemoveNullability = true,
 		};
 
+		internal static readonly NormalizeTypeVisitor IgnoreNullability = new NormalizeTypeVisitor {
+			ReplaceClassTypeParametersWithDummy = false,
+			ReplaceMethodTypeParametersWithDummy = false,
+			DynamicAndObject = false,
+			IntPtrToNInt = false,
+			TupleToUnderlyingType = false,
+			RemoveModOpt = true,
+			RemoveModReq = true,
+			RemoveNullability = true,
+		};
+
 		public bool EquivalentTypes(IType a, IType b)
 		{
 			a = a.AcceptVisitor(this);

ICSharpCode.Decompiler/Util/CollectionExtensions.cs

@@ -21,6 +21,12 @@ namespace ICSharpCode.Decompiler.Util
 		}
 #endif
 
+		public static IEnumerable<(int, A, B)> ZipWithIndex<A, B>(this IEnumerable<A> input1, IEnumerable<B> input2)
+		{
+			int index = 0;
+			return input1.Zip(input2, (a, b) => (index++, a, b));
+		}
+
 		public static IEnumerable<(A?, B?)> ZipLongest<A, B>(this IEnumerable<A> input1, IEnumerable<B> input2)
 		{
 			using (var it1 = input1.GetEnumerator())