From cb5960b8e00f5066806eb862749e0271e9950954 Mon Sep 17 00:00:00 2001
From: Siegfried Pammer <siegfriedpammer@gmail.com>
Date: Mon, 24 Dec 2018 00:55:39 +0100
Subject: [PATCH] Fix #1355: System.ArgumentException: An item with the same
 key has already been added in
 Decompiler.IL.Transforms.TransformExpressionTrees.ConvertLambda

---
 .../IL/Transforms/TransformExpressionTrees.cs                 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs b/ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs
index 814331853..75523b23a 100644
--- a/ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs
+++ b/ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs
@@ -214,6 +214,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 							return false;
 						if (!this.parameters.TryGetValue(v, out var value))
 							return false;
+						// Parameter variable cannot be used in two different compiler-generated expression trees,
+						// therefore we have to abort if the parameter is already mapped to a variable.
+						if (this.parameterMapping.ContainsKey(v))
+							return false;
 						var param = new ILVariable(VariableKind.Parameter, value.Item1, i) { Name = value.Item2 };
 						parameterMapping.Add(v, param);
 						parameterVariables.Add(param);