Add basic support for C# 8.0 enhanced using statements.

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -94,6 +94,7 @@
     <Compile Include="TestAssemblyResolver.cs" />
     <Compile Include="TestCases\Correctness\DeconstructionTests.cs" />
     <Compile Include="TestCases\Correctness\StringConcat.cs" />
+    <None Include="TestCases\Pretty\UsingVariables.cs" />
     <None Include="TestCases\Pretty\AsyncForeach.cs" />
     <Compile Include="TestCases\Pretty\DeconstructionTests.cs" />
     <Compile Include="TestCases\ILPretty\Issue2104.cs" />

ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs

@@ -109,13 +109,13 @@ namespace ICSharpCode.Decompiler.Tests
 		[Test]
 		public void FSharpUsing_Debug()
 		{
-			Run(settings: new DecompilerSettings { RemoveDeadStores = true });
+			Run(settings: new DecompilerSettings { RemoveDeadStores = true, UseEnhancedUsing = false });
 		}
 
 		[Test]
 		public void FSharpUsing_Release()
 		{
-			Run(settings: new DecompilerSettings { RemoveDeadStores = true });
+			Run(settings: new DecompilerSettings { RemoveDeadStores = true, UseEnhancedUsing = false });
 		}
 
 		[Test]

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -178,6 +178,15 @@ namespace ICSharpCode.Decompiler.Tests
 
 		[Test]
 		public void Using([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
+		{
+			RunForLibrary(
+				cscOptions: cscOptions,
+				decompilerSettings: new DecompilerSettings { UseEnhancedUsing = false }
+			);
+		}
+
+		[Test]
+		public void UsingVariables([ValueSource(nameof(dotnetCoreOnlyOptions))] CompilerOptions cscOptions)
 		{
 			RunForLibrary(cscOptions: cscOptions);
 		}
@@ -335,7 +344,10 @@ namespace ICSharpCode.Decompiler.Tests
 		[Test]
 		public void AsyncUsing([ValueSource(nameof(dotnetCoreOnlyOptions))] CompilerOptions cscOptions)
 		{
-			RunForLibrary(cscOptions: cscOptions);
+			RunForLibrary(
+				cscOptions: cscOptions,
+				decompilerSettings: new DecompilerSettings { UseEnhancedUsing = false }
+			);
 		}
 
 		[Test]

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

@@ -1,4 +1,22 @@
-using System.Collections.Generic;
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 

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

@@ -0,0 +1,93 @@
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System;
+//using System.Threading.Tasks;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public class UsingVariables
+	{
+		public IDisposable GetDisposable()
+		{
+			return null;
+		}
+
+		public IAsyncDisposable GetAsyncDisposable()
+		{
+			return null;
+		}
+
+		private void Use(IDisposable disposable)
+		{
+
+		}
+
+		private void Use(IAsyncDisposable disposable)
+		{
+
+		}
+
+		public void SimpleUsingVar()
+		{
+			Console.WriteLine("before using");
+			using IDisposable disposable = GetDisposable();
+			Console.WriteLine("inside using");
+			Use(disposable);
+		}
+
+		public void NotAUsingVar()
+		{
+			Console.WriteLine("before using");
+			using (IDisposable disposable = GetDisposable()) {
+				Console.WriteLine("inside using");
+				Use(disposable);
+			}
+			Console.WriteLine("outside using");
+		}
+
+		public void UsingVarInNestedBlocks(bool condition)
+		{
+			if (condition) {
+				using IDisposable disposable = GetDisposable();
+				Console.WriteLine("inside using");
+				Use(disposable);
+			}
+			Console.WriteLine("outside using");
+		}
+
+		public void MultipleUsingVars(IDisposable other)
+		{
+			Console.WriteLine("before using");
+			using IDisposable disposable = GetDisposable();
+			Console.WriteLine("inside outer using");
+			using IDisposable disposable2 = other;
+			Console.WriteLine("inside inner using");
+			Use(disposable);
+			Use(disposable2);
+		}
+
+		//public async Task SimpleUsingVarAsync(IAsyncDisposable other)
+		//{
+		//	Console.WriteLine("before using");
+		//	await using IAsyncDisposable asyncDisposable = GetAsyncDisposable();
+		//	Console.WriteLine("inside using");
+		//	Use(asyncDisposable);
+		//}
+	}
+}

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -1889,16 +1889,36 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 				WriteKeyword(UsingStatement.AwaitRole);
 			}
 			WriteKeyword(UsingStatement.UsingKeywordRole);
-			Space(policy.SpaceBeforeUsingParentheses);
-			LPar();
-			Space(policy.SpacesWithinUsingParentheses);
+			if (usingStatement.IsEnhanced) {
+				Space();
+			} else {
+				Space(policy.SpaceBeforeUsingParentheses);
+				LPar();
+				Space(policy.SpacesWithinUsingParentheses);
+			}
 
 			usingStatement.ResourceAcquisition.AcceptVisitor(this);
 
-			Space(policy.SpacesWithinUsingParentheses);
-			RPar();
+			if (usingStatement.IsEnhanced) {
+				Semicolon();
+			} else {
+				Space(policy.SpacesWithinUsingParentheses);
+				RPar();
+			}
 
-			WriteEmbeddedStatement(usingStatement.EmbeddedStatement);
+			if (usingStatement.IsEnhanced) {
+				if (usingStatement.EmbeddedStatement is BlockStatement blockStatement) {
+					StartNode(blockStatement);
+					foreach (var node in blockStatement.Statements) {
+						node.AcceptVisitor(this);
+					}
+					EndNode(blockStatement);
+				} else {
+					usingStatement.EmbeddedStatement.AcceptVisitor(this);
+				}
+			} else {
+				WriteEmbeddedStatement(usingStatement.EmbeddedStatement);
+			}
 
 			EndNode(usingStatement);
 		}

ICSharpCode.Decompiler/CSharp/Syntax/Statements/UsingStatement.cs

@@ -53,6 +53,8 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			get { return GetChildByRole(Roles.LPar); }
 		}
 
+		public bool IsEnhanced { get; set; }
+
 		/// <summary>
 		/// Either a VariableDeclarationStatement, or an Expression.
 		/// </summary>

ICSharpCode.Decompiler/CSharp/Transforms/PatternStatementTransform.cs

@@ -1123,5 +1123,23 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 			return base.VisitFixedStatement(fixedStatement);
 		}
 		#endregion
+
+		#region C# 8.0 Using variables
+		public override AstNode VisitUsingStatement(UsingStatement usingStatement)
+		{
+			usingStatement = (UsingStatement)base.VisitUsingStatement(usingStatement);
+			if (!context.Settings.UseEnhancedUsing)
+				return usingStatement;
+
+			if (usingStatement.GetNextStatement() != null || !(usingStatement.Parent is BlockStatement))
+				return usingStatement;
+
+			if (!(usingStatement.ResourceAcquisition is VariableDeclarationStatement))
+				return usingStatement;
+
+			usingStatement.IsEnhanced = true;
+			return usingStatement;
+		}
+		#endregion
 	}
 }

ICSharpCode.Decompiler/DecompilerSettings.cs

@@ -112,6 +112,7 @@ namespace ICSharpCode.Decompiler
 				readOnlyMethods = false;
 				asyncUsingAndForEachStatement = false;
 				asyncEnumerator = false;
+				useEnhancedUsing = false;
 				staticLocalFunctions = false;
 				ranges = false;
 				switchExpressions = false;
@@ -474,6 +475,23 @@ namespace ICSharpCode.Decompiler
 			}
 		}
 
+		bool useEnhancedUsing = true;
+
+		/// <summary>
+		/// Use enhanced using statements.
+		/// </summary>
+		[Category("C# 8.0 / VS 2019")]
+		[Description("DecompilerSettings.UseEnhancedUsing")]
+		public bool UseEnhancedUsing {
+			get { return useEnhancedUsing; }
+			set {
+				if (useEnhancedUsing != value) {
+					useEnhancedUsing = value;
+					OnPropertyChanged();
+				}
+			}
+		}
+
 		bool alwaysUseBraces = true;
 
 		/// <summary>

ILSpy/Properties/Resources.Designer.cs

@@ -1100,6 +1100,15 @@ namespace ICSharpCode.ILSpy.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Use enhanced using variable declarations.
+        /// </summary>
+        public static string DecompilerSettings_UseEnhancedUsing {
+            get {
+                return ResourceManager.GetString("DecompilerSettings.UseEnhancedUsing", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Use expression-bodied member syntax for get-only properties.
         /// </summary>

ILSpy/Properties/Resources.resx

@@ -396,6 +396,9 @@ Are you sure you want to continue?</value>
   <data name="DecompilerSettings.UseDiscards" xml:space="preserve">
     <value>Use discards</value>
   </data>
+  <data name="DecompilerSettings.UseEnhancedUsing" xml:space="preserve">
+    <value>Use enhanced using variable declarations</value>
+  </data>
   <data name="DecompilerSettings.UseExpressionBodiedMemberSyntaxForGetOnlyProperties" xml:space="preserve">
     <value>Use expression-bodied member syntax for get-only properties</value>
   </data>