Add option for `string.Concat` decompilation.

ICSharpCode.Decompiler/CSharp/Transforms/ReplaceMethodCallsWithOperators.cs

@@ -16,11 +16,8 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
-using System;
-using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
-using System.Text;
 
 using ICSharpCode.Decompiler.CSharp.Syntax;
 using ICSharpCode.Decompiler.CSharp.Syntax.PatternMatching;
@@ -59,7 +56,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			var arguments = invocationExpression.Arguments.ToArray();
 
 			// Reduce "String.Concat(a, b)" to "a + b"
-			if (IsStringConcat(method) && CheckArgumentsForStringConcat(arguments))
+			if (IsStringConcat(method) && context.Settings.StringConcat && CheckArgumentsForStringConcat(arguments))
 			{
 				bool isInExpressionTree = invocationExpression.Ancestors.OfType<LambdaExpression>().Any(
 					lambda => lambda.Annotation<IL.ILFunction>()?.Kind == IL.ILFunctionKind.ExpressionTree);

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -443,6 +443,24 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
+		bool stringConcat = true;
+
+		/// <summary>
+		/// Decompile 'string.Concat(a, b)' calls into 'a + b'.
+		/// </summary>
+		[Category("C# 1.0 / VS .NET")]
+		[Description("DecompilerSettings.StringConcat")]
+		public bool StringConcat {
+			get { return stringConcat; }
+			set {
+				if (stringConcat != value)
+				{
+					stringConcat = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool liftNullables = true;
 
 		/// <summary>

ILSpy/Properties/Resources.Designer.cs

@@ -1118,6 +1118,15 @@ namespace ICSharpCode.ILSpy.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Decompile &apos;string.Concat(a, b)&apos; calls into &apos;a + b&apos;.
+        /// </summary>
+        public static string DecompilerSettings_StringConcat {
+            get {
+                return ResourceManager.GetString("DecompilerSettings.StringConcat", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Switch expressions.
         /// </summary>

ILSpy/Properties/Resources.resx

@@ -402,6 +402,9 @@ Are you sure you want to continue?</value>
   <data name="DecompilerSettings.SparseIntegerSwitch" xml:space="preserve">
     <value>Detect switch on integer even if IL code does not use a jump table</value>
   </data>
+  <data name="DecompilerSettings.StringConcat" xml:space="preserve">
+    <value>Decompile 'string.Concat(a, b)' calls into 'a + b'</value>
+  </data>
   <data name="DecompilerSettings.SwitchExpressions" xml:space="preserve">
     <value>Switch expressions</value>
   </data>