DelegateConstruction:

- add support for unknown delegate construction pattern. The method is compiler-generated, but has no compiler-generated name, we should be able to infer lambda usage from anonymous types used in the signature (i. e., the method can only be used as lambda, because that's where type names are optional).
- Add CombineExitsTransform in DelegateConstruction: this allows combining lambdas with multiple return statements into a single expression (as it is expected by query expressions).

ICSharpCode.Decompiler/ICSharpCode.Decompiler.csproj

@@ -74,7 +74,7 @@
     <Compile Include="CSharp\Syntax\ErrorNode.cs" />
     <Compile Include="CSharp\Syntax\Expressions\AnonymousMethodExpression.cs" />
     <Compile Include="CSharp\Syntax\Expressions\AnonymousTypeCreateExpression.cs" />
-    <Compile Include="CSharp\Syntax\Expressions\ArrayCreateExpression.cs"  />
+    <Compile Include="CSharp\Syntax\Expressions\ArrayCreateExpression.cs" />
     <Compile Include="CSharp\Syntax\Expressions\ArrayInitializerExpression.cs" />
     <Compile Include="CSharp\Syntax\Expressions\AsExpression.cs" />
     <Compile Include="CSharp\Syntax\Expressions\AssignmentExpression.cs" />
@@ -265,6 +265,7 @@
     <Compile Include="CSharp\Transforms\AddXmlDocumentationTransform.cs" />
     <Compile Include="DecompileRun.cs" />
     <Compile Include="Disassembler\ILParser.cs" />
+    <Compile Include="IL\Transforms\CombineExitsTransform.cs" />
     <Compile Include="IL\Transforms\ReduceNestingTransform.cs" />
     <Compile Include="IL\Transforms\LocalFunctionDecompiler.cs" />
     <Compile Include="IL\Transforms\UserDefinedLogicTransform.cs" />

ICSharpCode.Decompiler/IL/Transforms/CombineExitsTransform.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace ICSharpCode.Decompiler.IL.Transforms
+{
+	class CombineExitsTransform : IILTransform
+	{
+		public void Run(ILFunction function, ILTransformContext context)
+		{
+			if (!(function.Body is BlockContainer container && container.Blocks.Count == 1))
+				return;
+			var block = container.EntryPoint;
+			if (block.Kind != BlockKind.ControlFlow)
+				return;
+			if (!(block.Instructions.SecondToLastOrDefault() is IfInstruction ifInst && block.Instructions.LastOrDefault() is Leave leave))
+				return;
+			if (!ifInst.FalseInst.MatchNop())
+				return;
+			if (!(Block.Unwrap(ifInst.TrueInst) is Leave leave2))
+				return;
+			if (!(leave.IsLeavingFunction && leave2.IsLeavingFunction))
+				return;
+			if (leave.Value.MatchNop() || leave2.Value.MatchNop())
+				return;
+			IfInstruction value = new IfInstruction(ifInst.Condition, leave.Value, leave2.Value);
+			Leave combinedLeave = new Leave(leave.TargetContainer, value);
+			ifInst.ReplaceWith(combinedLeave);
+			block.Instructions.RemoveAt(combinedLeave.ChildIndex + 1);
+		}
+	}
+}

ICSharpCode.Decompiler/IL/Transforms/DelegateConstruction.cs

@@ -105,13 +105,24 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		
 		static bool IsAnonymousMethod(ITypeDefinition decompiledTypeDefinition, IMethod method)
 		{
-			if (method == null || !(method.HasGeneratedName() || method.Name.Contains("$")))
+			if (method == null || !(method.HasGeneratedName() || method.Name.Contains("$") || ContainsAnonymousType(method)))
 				return false;
 			if (!(method.IsCompilerGeneratedOrIsInCompilerGeneratedClass() || IsPotentialClosure(decompiledTypeDefinition, method.DeclaringTypeDefinition)))
 				return false;
 			return true;
 		}
-		
+
+		static bool ContainsAnonymousType(IMethod method)
+		{
+			if (method.ReturnType.ContainsAnonymousType())
+				return true;
+			foreach (var p in method.Parameters) {
+				if (p.Type.ContainsAnonymousType())
+					return true;
+			}
+			return false;
+		}
+
 		static bool IsPotentialClosure(ITypeDefinition decompiledTypeDefinition, ITypeDefinition potentialDisplayClass)
 		{
 			if (potentialDisplayClass == null || !potentialDisplayClass.IsCompilerGeneratedOrIsInCompilerGeneratedClass())
@@ -178,7 +189,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			}
 
 			var nestedContext = new ILTransformContext(context, function);
-			function.RunTransforms(CSharpDecompiler.GetILTransforms().TakeWhile(t => !(t is DelegateConstruction)), nestedContext);
+			function.RunTransforms(CSharpDecompiler.GetILTransforms().TakeWhile(t => !(t is DelegateConstruction)).Concat(GetTransforms()), nestedContext);
 			function.AcceptVisitor(new ReplaceDelegateTargetVisitor(target, function.Variables.SingleOrDefault(v => v.Index == -1 && v.Kind == VariableKind.Parameter)));
 			// handle nested lambdas
 			((IILTransform)new DelegateConstruction()).Run(function, nestedContext);
@@ -186,7 +197,12 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			function.AddILRange(value.Arguments[1].ILRange);
 			return function;
 		}
-		
+
+		private IEnumerable<IILTransform> GetTransforms()
+		{
+			yield return new CombineExitsTransform();
+		}
+
 		/// <summary>
 		/// Replaces loads of 'this' with the target expression.
 		/// Async delegates use: ldobj(ldloca this).