From bbaddf84ccc64e3669e81a178210ca6f972c734d Mon Sep 17 00:00:00 2001
From: Daniel Grunwald <daniel@danielgrunwald.de>
Date: Thu, 3 Jun 2021 16:33:43 +0200
Subject: [PATCH] Fix #2424: Suppress the string==null special-case within the
 string class itself.

---
 ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs | 14 +++-----------
 .../CSharp/Resolver/CSharpResolver.cs              |  2 +-
 2 files changed, 4 insertions(+), 12 deletions(-)

diff --git a/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs b/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
index 99baef78e..c5ebf5bf7 100644
--- a/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
+++ b/ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs
@@ -930,16 +930,7 @@ namespace ICSharpCode.Decompiler.CSharp
 					.WithILInstruction(inst);
 			}
 
-			OperatorResolveResult rr;
-			if (left.Type.IsKnownType(KnownTypeCode.String) && right.Type.IsKnownType(KnownTypeCode.String))
-			{
-				rr = null; // it's a string comparison by-value, which is not a reference comparison
-			}
-			else
-			{
-				rr = resolver.ResolveBinaryOperator(inst.Kind.ToBinaryOperatorType(), left.ResolveResult, right.ResolveResult)
-					as OperatorResolveResult;
-			}
+			OperatorResolveResult rr = resolver.ResolveBinaryOperator(inst.Kind.ToBinaryOperatorType(), left.ResolveResult, right.ResolveResult) as OperatorResolveResult;
 			if (rr == null || rr.IsError || rr.UserDefinedOperatorMethod != null
 				|| NullableType.GetUnderlyingType(rr.Operands[0].Type).GetStackType() != inst.InputType
 				|| !rr.Type.IsKnownType(KnownTypeCode.Boolean))
@@ -1021,7 +1012,8 @@ namespace ICSharpCode.Decompiler.CSharp
 			if (lhs.Type.Kind == TypeKind.Null)
 				ExtensionMethods.Swap(ref lhs, ref rhs);
 			return rhs.Type.Kind == TypeKind.Null
-				&& (lhs.Type.Kind == TypeKind.Delegate || lhs.Type.IsKnownType(KnownTypeCode.String));
+				&& (lhs.Type.Kind == TypeKind.Delegate || lhs.Type.IsKnownType(KnownTypeCode.String))
+				&& lhs.Type.GetDefinition() != decompilationContext.CurrentTypeDefinition;
 		}
 
 		ExpressionWithResolveResult CreateBuiltinBinaryOperator(
diff --git a/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs b/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs
index 27e173e1b..23171a906 100644
--- a/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs
+++ b/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs
@@ -1310,7 +1310,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 			if (operatorName == null)
 				return EmptyList<IMethod>.Instance;
 			TypeCode c = ReflectionHelper.GetTypeCode(type);
-			if (TypeCode.Boolean <= c && c <= TypeCode.Decimal || c == TypeCode.String)
+			if (TypeCode.Boolean <= c && c <= TypeCode.Decimal)
 			{
 				// The .NET framework contains some of C#'s built-in operators as user-defined operators.
 				// However, we must not use those as user-defined operators (we would skip numeric promotion).