From 2fb90b49e0e03cf45fd069438a94373d4a64d782 Mon Sep 17 00:00:00 2001
From: Siegfried Pammer <siegfriedpammer@gmail.com>
Date: Mon, 23 Jun 2025 21:15:08 +0200
Subject: [PATCH] Adjust string.Concat handling in
 ReplaceMethodCallsWithOperators to support unexpanded string.Concat calls.

---
 .../Transforms/ReplaceMethodCallsWithOperators.cs    | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/ICSharpCode.Decompiler/CSharp/Transforms/ReplaceMethodCallsWithOperators.cs b/ICSharpCode.Decompiler/CSharp/Transforms/ReplaceMethodCallsWithOperators.cs
index 36624535b..287d7e3f3 100644
--- a/ICSharpCode.Decompiler/CSharp/Transforms/ReplaceMethodCallsWithOperators.cs
+++ b/ICSharpCode.Decompiler/CSharp/Transforms/ReplaceMethodCallsWithOperators.cs
@@ -57,8 +57,18 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			var arguments = invocationExpression.Arguments.ToArray();
 
 			// Reduce "String.Concat(a, b)" to "a + b"
-			if (IsStringConcat(method) && context.Settings.StringConcat && CheckArgumentsForStringConcat(arguments))
+			if (IsStringConcat(method) && context.Settings.StringConcat)
 			{
+				if (arguments is [ArrayCreateExpression ace] && method.Parameters is [{ Type: ArrayType }])
+				{
+					arguments = ace.Initializer.Elements.ToArray();
+				}
+
+				if (!CheckArgumentsForStringConcat(arguments))
+				{
+					return;
+				}
+
 				bool isInExpressionTree = invocationExpression.Ancestors.OfType<LambdaExpression>().Any(
 					lambda => lambda.Annotation<IL.ILFunction>()?.Kind == IL.ILFunctionKind.ExpressionTree);
 				Expression arg0 = arguments[0].Detach();