Add support for static local function

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -1001,6 +1001,9 @@ namespace ICSharpCode.Decompiler.CSharp
 				if (function.IsAsync) {
 					stmt.Modifiers |= Modifiers.Async;
 				}
+				if (settings.StaticLocalFunctions && function.Method.IsStatic && function.ReducedMethod.NumberOfCompilerGeneratedParameters == 0) {
+					stmt.Modifiers |= Modifiers.Static;
+				}
 				stmt.AddAnnotation(new MemberResolveResult(null, function.ReducedMethod));
 				return stmt;
 			}

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -110,12 +110,13 @@ namespace ICSharpCode.Decompiler
 				readOnlyMethods = false;
 				asyncUsingAndForEachStatement = false;
 				asyncEnumerator = false;
+				staticLocalFunctions = false;
 			}
 		}
 
 		public CSharp.LanguageVersion GetMinimumRequiredVersion()
 		{
-			if (nullableReferenceTypes || readOnlyMethods || asyncEnumerator || asyncUsingAndForEachStatement)
+			if (nullableReferenceTypes || readOnlyMethods || asyncEnumerator || asyncUsingAndForEachStatement || staticLocalFunctions)
 				return CSharp.LanguageVersion.CSharp8_0;
 			if (introduceUnmanagedConstraint || tupleComparisons || stackAllocInitializers)
 				return CSharp.LanguageVersion.CSharp7_3;
@@ -1064,6 +1065,23 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
+		bool staticLocalFunctions = true;
+
+		/// <summary>
+		/// Gets/Sets whether C# 8.0 static local functions should be transformed.
+		/// </summary>
+		[Category("C# 8.0 / VS 2019")]
+		[Description("DecompilerSettings.IntroduceStaticLocalFunctions")]
+		public bool StaticLocalFunctions {
+			get { return staticLocalFunctions; }
+			set {
+				if (staticLocalFunctions != value) {
+					staticLocalFunctions = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool nullableReferenceTypes = true;
 
 		/// <summary>

ILSpy/Properties/Resources.Designer.cs

@@ -772,6 +772,15 @@ namespace ICSharpCode.ILSpy.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Introduce static local functions.
+        /// </summary>
+        public static string DecompilerSettings_IntroduceStaticLocalFunctions {
+            get {
+                return ResourceManager.GetString("DecompilerSettings.IntroduceStaticLocalFunctions", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to IsByRefLikeAttribute should be replaced with &apos;ref&apos; modifiers on structs.
         /// </summary>

ILSpy/Properties/Resources.resx

@@ -775,4 +775,7 @@ Are you sure you want to continue?</value>
   <data name="DecompilerSettings.DetectAsyncUsingAndForeachStatements" xml:space="preserve">
     <value>Detect awaited using and foreach statements</value>
   </data>
+  <data name="DecompilerSettings.IntroduceStaticLocalFunctions" xml:space="preserve">
+    <value>Introduce static local functions</value>
+  </data>
 </root>