Fix #1574: When re-introducing an explicit cast for an implicit user-defined conversion; ensure we use a direct cast and don't go through the code path for builtin conversions.

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

@@ -89,6 +89,7 @@
     <Compile Include="TestCases\ILPretty\Issue1323.cs" />
     <Compile Include="TestCases\Pretty\CustomAttributes2.cs" />
     <Compile Include="TestCases\Pretty\EnumTests.cs" />
+    <Compile Include="TestCases\Pretty\UserDefinedConversions.cs" />
     <None Include="TestCases\ILPretty\Unsafe.il" />
     <None Include="TestCases\Pretty\NullableRefTypes.cs" />
     <Compile Include="TestCases\Pretty\TypeMemberTests.cs" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -425,6 +425,12 @@ namespace ICSharpCode.Decompiler.Tests
 			RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public void UserDefinedConversions([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
+		{
+			RunForLibrary(cscOptions: cscOptions);
+		}
+
 		[Test]
 		public void Discards([ValueSource(nameof(roslynOnlyOptions))] CompilerOptions cscOptions)
 		{

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

@@ -0,0 +1,134 @@
+// Copyright (c) 2019 Daniel Grunwald
+// 
+// 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.
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	internal class T01Issue1574
+	{
+		private struct A
+		{
+			private bool val;
+
+			public static implicit operator bool(A a)
+			{
+				return a.val;
+			}
+		}
+
+		private struct C
+		{
+			private int val;
+
+			public static implicit operator C(bool b)
+			{
+				return default(C);
+			}
+		}
+
+		private C ChainedConversion()
+		{
+			return (bool)default(A);
+		}
+
+		public void Call_Overloaded()
+		{
+			Overloaded((bool)default(A));
+		}
+
+		private void Overloaded(A a)
+		{
+		}
+
+		private void Overloaded(bool a)
+		{
+		}
+	}
+
+	internal class T02BothDirectAndChainedConversionPossible
+	{
+		private struct A
+		{
+			private bool val;
+
+			public static implicit operator bool(A a)
+			{
+				return a.val;
+			}
+		}
+
+		private struct C
+		{
+			private int val;
+
+			public static implicit operator C(bool b)
+			{
+				return default(C);
+			}
+
+			public static implicit operator C(A a)
+			{
+				return default(C);
+			}
+
+			public static bool operator ==(C a, C b)
+			{
+				return true;
+			}
+			public static bool operator !=(C a, C b)
+			{
+				return false;
+			}
+		}
+
+		private C DirectConvert(A a)
+		{
+			return a;
+		}
+
+		private C IndirectConvert(A a)
+		{
+			return (bool)a;
+		}
+
+		private C? LiftedDirectConvert(A? a)
+		{
+			return a;
+		}
+
+		private C? LiftedIndirectConvert(A? a)
+		{
+			return (bool?)a;
+		}
+
+		private bool Compare(A a, C c)
+		{
+			return a == c;
+		}
+
+		private void LiftedCompare(A? a, C? c)
+		{
+			UseBool(a == c);
+			UseBool(a == default(C));
+			UseBool(c == default(A));
+		}
+
+		private void UseBool(bool b)
+		{
+		}
+	}
+}

ICSharpCode.Decompiler/CSharp/Annotations.cs

@@ -240,4 +240,18 @@ namespace ICSharpCode.Decompiler.CSharp
 			this.Leave = leave;
 		}
 	}
+
+	/// <summary>
+	/// Annotates an expression when an implicit user-defined conversion was omitted.
+	/// </summary>
+	public class ImplicitConversionAnnotation
+	{
+		public readonly ConversionResolveResult ConversionResolveResult;
+		public IType TargetType => ConversionResolveResult.Type;
+
+		public ImplicitConversionAnnotation(ConversionResolveResult conversionResolveResult)
+		{
+			this.ConversionResolveResult = conversionResolveResult;
+		}
+	}
 }

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -191,7 +191,11 @@ namespace ICSharpCode.Decompiler.CSharp
 									conversion.Input.Type,
 									type, targetType
 								)) {
-								return this.UnwrapChild(cast.Expression);
+								var result = this.UnwrapChild(cast.Expression);
+								if (conversion.Conversion.IsUserDefined) {
+									result.Expression.AddAnnotation(new ImplicitConversionAnnotation(conversion));
+								}
+								return result;
 							} else if (Expression is ObjectCreateExpression oce && conversion.Conversion.IsMethodGroupConversion
 									&& oce.Arguments.Count == 1 && expressionBuilder.settings.UseImplicitMethodGroupConversion) {
 								return this.UnwrapChild(oce.Arguments.Single());
@@ -211,6 +215,18 @@ namespace ICSharpCode.Decompiler.CSharp
 			if (targetType.Kind == TypeKind.Unknown || targetType.Kind == TypeKind.Void || targetType.Kind == TypeKind.None) {
 				return this; // don't attempt to insert cast to '?' or 'void' as these are not valid.
 			}
+			var convAnnotation = this.Expression.Annotation<ImplicitConversionAnnotation>();
+			if (convAnnotation != null) {
+				// If an implicit user-defined conversion was stripped from this expression;
+				// it needs to be re-introduced before we can apply other casts to this expression.
+				// This happens when the CallBuilder discovers that the conversion is necessary in
+				// order to choose the correct overload.
+				this.Expression.RemoveAnnotations<ImplicitConversionAnnotation>();
+				return new CastExpression(expressionBuilder.ConvertType(convAnnotation.TargetType), Expression)
+					.WithoutILInstruction()
+					.WithRR(convAnnotation.ConversionResolveResult)
+					.ConvertTo(targetType, expressionBuilder, checkForOverflow, allowImplicitConversion);
+			}
 			if (Expression is TupleExpression tupleExpr && targetType is TupleType targetTupleType
 				&& tupleExpr.Elements.Count == targetTupleType.ElementTypes.Length)
 			{
@@ -231,8 +247,9 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 			var compilation = expressionBuilder.compilation;
 			var conversions = Resolver.CSharpConversions.Get(compilation);
-			if (ResolveResult is ConversionResolveResult conv && Expression is CastExpression cast2 &&
-				CastCanBeMadeImplicit(conversions, conv.Conversion, conv.Input.Type, type, targetType))
+			if (ResolveResult is ConversionResolveResult conv && Expression is CastExpression cast2
+				&& !conv.Conversion.IsUserDefined
+				&& CastCanBeMadeImplicit(conversions, conv.Conversion, conv.Input.Type, type, targetType))
 			{
 				var unwrapped = this.UnwrapChild(cast2.Expression);
 				if (allowImplicitConversion)