From 1bba26cdb02ba05ae11e272713155ec9adfc52bd Mon Sep 17 00:00:00 2001
From: ds5678 <49847914+ds5678@users.noreply.github.com>
Date: Mon, 5 May 2025 16:48:55 -0700
Subject: [PATCH] Fix stack overflow exception in CSharpResolver

---
 .../ICSharpCode.Decompiler.Tests.csproj       |  2 +
 .../ILPrettyTestRunner.cs                     |  6 +++
 .../TestCases/ILPretty/Issue3466.cs           | 14 ++++++
 .../TestCases/ILPretty/Issue3466.il           | 49 +++++++++++++++++++
 .../CSharp/Resolver/CSharpResolver.cs         |  2 +-
 5 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.cs
 create mode 100644 ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.il

diff --git a/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj b/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj
index 5a89e7178..f7c49347a 100644
--- a/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj
+++ b/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj
@@ -94,6 +94,7 @@
     <None Include="TestCases\ILPretty\GuessAccessors.il" />
     <None Include="TestCases\ILPretty\Issue2260SwitchString.il" />
     <None Include="TestCases\ILPretty\Issue3442.il" />
+    <None Include="TestCases\ILPretty\Issue3466.il" />
     <None Include="TestCases\ILPretty\MonoFixed.il" />
     <None Include="TestCases\Correctness\NonGenericConstrainedCallVirt.il" />
     <None Include="TestCases\ILPretty\UnknownTypes.cs" />
@@ -135,6 +136,7 @@
     <Compile Include="TestAssemblyResolver.cs" />
     <Compile Include="TestCases\ILPretty\Issue3421.cs" />
     <Compile Include="TestCases\ILPretty\Issue3442.cs" />
+    <Compile Include="TestCases\ILPretty\Issue3466.cs" />
     <Compile Include="TestCases\ILPretty\MonoFixed.cs" />
     <Compile Include="TestCases\Pretty\Comparisons.cs" />
     <Compile Include="TestCases\Pretty\GloballyQualifiedTypeInStringInterpolation.cs" />
diff --git a/ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs b/ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs
index aebbf8c09..abdc031fa 100644
--- a/ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs
+++ b/ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs
@@ -219,6 +219,12 @@ namespace ICSharpCode.Decompiler.Tests
 			await Run();
 		}
 
+		[Test]
+		public async Task Issue3466()
+		{
+			await Run();
+		}
+
 		[Test]
 		public async Task Issue2260SwitchString()
 		{
diff --git a/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.cs b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.cs
new file mode 100644
index 000000000..875cae068
--- /dev/null
+++ b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.cs
@@ -0,0 +1,14 @@
+namespace ICSharpCode.Decompiler.Tests.TestCases.ILPretty
+{
+	public class Issue3466<T>
+	{
+		public static implicit operator Issue3466<T>(T t)
+		{
+			return null;
+		}
+		public static bool M(Issue3466<object> x)
+		{
+			return x != null;
+		}
+	}
+}
diff --git a/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.il b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.il
new file mode 100644
index 000000000..a6df20cc4
--- /dev/null
+++ b/ICSharpCode.Decompiler.Tests/TestCases/ILPretty/Issue3466.il
@@ -0,0 +1,49 @@
+.assembly extern System.Runtime
+{
+	.publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
+	.ver 4:0:0:0
+}
+
+.assembly Issue3466
+{
+	.hash algorithm 0x00008004 // SHA1
+	.ver 0:0:0:0
+}
+
+.class public auto ansi beforefieldinit ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3466`1<T>
+	extends [System.Runtime]System.Object
+{
+	.method public hidebysig specialname static 
+		class ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3466`1<!T> op_Implicit (
+			!T t
+		) cil managed 
+	{
+		.maxstack 8
+
+		IL_0000: ldnull
+		IL_0001: ret
+	}
+
+	.method public final hidebysig static bool M(class ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3466`1<object> x) cil managed 
+	{
+		.maxstack 8
+
+		IL_0000: ldarg.0
+		IL_0001: brtrue.s IL_0004
+		IL_0002: ldc.i4.0
+		IL_0003: br.s IL_0005
+		IL_0004: ldc.i4.1
+		IL_0005: ret
+	}
+
+	.method public hidebysig specialname rtspecialname 
+		instance void .ctor () cil managed 
+	{
+		.maxstack 8
+
+		IL_0000: ldarg.0
+		IL_0001: call instance void [System.Runtime]System.Object::.ctor()
+		IL_0006: ret
+	}
+
+}
\ No newline at end of file
diff --git a/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs b/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs
index 9e556e6cd..d60724bcd 100644
--- a/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs
+++ b/ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs
@@ -805,7 +805,7 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 					}
 					if (op == BinaryOperatorType.Equality || op == BinaryOperatorType.InEquality)
 					{
-						if (lhsType.IsReferenceType == true && rhsType.IsReferenceType == true
+						if (lhsType.IsReferenceType == true && rhsType.IsReferenceType == true && rhsType.Kind != TypeKind.Null
 							&& (conversions.IdentityConversion(lhsType, rhsType)
 								|| conversions.ExplicitConversion(lhsType, rhsType).IsReferenceConversion
 								|| conversions.ExplicitConversion(rhsType, lhsType).IsReferenceConversion))