Add option: 'ref' extension methods

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

@@ -221,12 +221,21 @@ namespace ICSharpCode.Decompiler.Tests.Pretty
 		{
 
 		}
+#if CS72
+		public static void Do(this ref DateTime test)
+		{
+
+		}
+#endif
 
-		public static void Do2(this int test)
+		public static void Do2(this int test, DateTime date)
 		{
 			test.Do();
 			((IEnumerable<int>)null).Any();
 			((object)null).Do();
+#if CS72
+			date.Do();
+#endif
 		}
 	}
 }

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceExtensionMethods.cs

@@ -137,7 +137,15 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			}
 			if (!CanTransformToExtensionMethodCall(resolver, method, typeArguments, target, args, argNames))
 				return;
-			if (firstArgument is NullReferenceExpression) {
+			if (firstArgument is DirectionExpression dirExpr) {
+				if (dirExpr.FieldDirection != FieldDirection.Ref)
+					return;
+				if (!context.Settings.RefExtensionMethods)
+					return;
+				firstArgument = dirExpr.Expression;
+				target = firstArgument.GetResolveResult();
+				dirExpr.Detach();
+			} else if (firstArgument is NullReferenceExpression) {
 				Debug.Assert(context.RequiredNamespacesSuperset.Contains(method.Parameters[0].Type.Namespace));
 				firstArgument = firstArgument.ReplaceWith(expr => new CastExpression(context.TypeSystemAstBuilder.ConvertType(method.Parameters[0].Type), expr.Detach()));
 			}

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -97,6 +97,7 @@ namespace ICSharpCode.Decompiler
 				introduceReadonlyAndInModifiers = false;
 				introduceRefModifiersOnStructs = false;
 				nonTrailingNamedArguments = false;
+				refExtensionMethods = false;
 			}
 			if (languageVersion < CSharp.LanguageVersion.CSharp7_3) {
 				introduceUnmanagedConstraint = false;
@@ -114,7 +115,7 @@ namespace ICSharpCode.Decompiler
 				return CSharp.LanguageVersion.CSharp8_0;
 			if (introduceUnmanagedConstraint || tupleComparisons || stackAllocInitializers)
 				return CSharp.LanguageVersion.CSharp7_3;
-			if (introduceRefModifiersOnStructs || introduceReadonlyAndInModifiers || nonTrailingNamedArguments)
+			if (introduceRefModifiersOnStructs || introduceReadonlyAndInModifiers || nonTrailingNamedArguments || refExtensionMethods)
 				return CSharp.LanguageVersion.CSharp7_2;
 			// C# 7.1 missing
 			if (outVariables || tupleTypes || tupleConversions || discards || localFunctions)
@@ -626,6 +627,23 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
+		bool refExtensionMethods = true;
+
+		/// <summary>
+		/// Gets/Sets whether to use C# 7.2 'ref' extension methods.
+		/// </summary>
+		[Category("C# 7.2 / VS 2017.4")]
+		[Description("DecompilerSettings.AllowExtensionMethodSyntaxOnRef")]
+		public bool RefExtensionMethods {
+			get { return refExtensionMethods; }
+			set {
+				if (refExtensionMethods != value) {
+					refExtensionMethods = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool stringInterpolation = true;
 
 		/// <summary>

ILSpy/Properties/Resources.Designer.cs

@@ -474,6 +474,15 @@ namespace ICSharpCode.ILSpy.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Use &apos;ref&apos; extension methods.
+        /// </summary>
+        public static string DecompilerSettings_AllowExtensionMethodSyntaxOnRef {
+            get {
+                return ResourceManager.GetString("DecompilerSettings.AllowExtensionMethodSyntaxOnRef", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Always cast targets of explicit interface implementation calls.
         /// </summary>

ILSpy/Properties/Resources.resx

@@ -729,4 +729,7 @@
   <data name="CannotAnalyzeMissingRef" xml:space="preserve">
     <value>Entity could not be resolved. Cannot analyze entities from missing assembly references. Add the missing reference and try again.</value>
   </data>
+  <data name="DecompilerSettings.AllowExtensionMethodSyntaxOnRef" xml:space="preserve">
+    <value>Use 'ref' extension methods</value>
+  </data>
 </root>