From 850ffe593dfd2b86cef9a6e315a54ca46d572b43 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maximilian=20Schm=C3=B6cker?= <m.schmoecker@brickfire.eu>
Date: Tue, 5 Aug 2025 23:39:02 +0200
Subject: [PATCH] Fix methods with mandatory arguments ignore disabled
 OptionalArguments setting

---
 .../ICSharpCode.Decompiler.Tests.csproj       |  1 +
 .../PrettyTestRunner.cs                       | 11 +++++++++++
 .../Pretty/OptionalArgumentsDisabled.cs       | 19 +++++++++++++++++++
 ICSharpCode.Decompiler/CSharp/CallBuilder.cs  |  3 ++-
 4 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 ICSharpCode.Decompiler.Tests/TestCases/Pretty/OptionalArgumentsDisabled.cs

diff --git a/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj b/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj
index 0282f9d00..6529de6ed 100644
--- a/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj
+++ b/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj
@@ -251,6 +251,7 @@
     <Compile Include="TestCases\Pretty\ConstantsTests.cs" />
     <Compile Include="TestCases\Pretty\CS73_StackAllocInitializers.cs" />
     <Compile Include="TestCases\Pretty\OptionalArguments.cs" />
+    <Compile Include="TestCases\Pretty\OptionalArgumentsDisabled.cs" />
     <Compile Include="TestCases\Pretty\CustomShortCircuitOperators.cs" />
     <Compile Include="TestCases\Pretty\ReduceNesting.cs" />
     <Compile Include="TestCases\Pretty\InterfaceTests.cs" />
diff --git a/ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs b/ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs
index d67877e72..3df322aaf 100644
--- a/ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs
+++ b/ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs
@@ -599,6 +599,17 @@ namespace ICSharpCode.Decompiler.Tests
 			await RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public async Task OptionalArgumentsDisabled([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(
+				cscOptions: cscOptions,
+				configureDecompiler: settings => {
+					settings.OptionalArguments = false;
+				}
+			);
+		}
+
 		[Test]
 		public async Task Comparisons([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{
diff --git a/ICSharpCode.Decompiler.Tests/TestCases/Pretty/OptionalArgumentsDisabled.cs b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/OptionalArgumentsDisabled.cs
new file mode 100644
index 000000000..b33456f2c
--- /dev/null
+++ b/ICSharpCode.Decompiler.Tests/TestCases/Pretty/OptionalArgumentsDisabled.cs
@@ -0,0 +1,19 @@
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public class OptionalArgumentsDisabled
+	{
+		public void Test()
+		{
+			MixedArguments("123", 0, 0);
+			OnlyOptionalArguments(0, 0);
+		}
+
+		public void MixedArguments(string msg, int a = 0, int b = 0)
+		{
+		}
+
+		public void OnlyOptionalArguments(int a = 0, int b = 0)
+		{
+		}
+	}
+}
diff --git a/ICSharpCode.Decompiler/CSharp/CallBuilder.cs b/ICSharpCode.Decompiler/CSharp/CallBuilder.cs
index 2ff1ce4d1..5027b7370 100644
--- a/ICSharpCode.Decompiler/CSharp/CallBuilder.cs
+++ b/ICSharpCode.Decompiler/CSharp/CallBuilder.cs
@@ -967,7 +967,8 @@ namespace ICSharpCode.Decompiler.CSharp
 				}
 				else
 				{
-					firstOptionalArgumentIndex = -2;
+					if (firstOptionalArgumentIndex != -1)
+						firstOptionalArgumentIndex = -2;
 				}
 				if (parameter.IsParams && i + 1 == callArguments.Count && argumentToParameterMap == null)
 				{