Fix S1144 FP: Unused fields in class with StructLayout when struct is in deep hierarchy class

[tkouba]

Description

When class has StructLayout, we need all its props for memory allocation. Even if its embedded in deep class hierarchy. Similar to issue #6912, but fix is not working in edge cases.

Repro steps

For example:

    partial class WindowsCredentialService
    {
        class NativeMethods
        {
            [StructLayout(LayoutKind.Sequential)]
            internal struct Credential
            {
                public int Flags;
                public int Type;
                [MarshalAs(UnmanagedType.LPWStr)]
                public string TargetName;
                [MarshalAs(UnmanagedType.LPWStr)]
                public string Comment;
                public long LastWritten;
                public int CredentialBlobSize;
                public IntPtr CredentialBlob;
                public int Persist;
                public int AttributeCount;
                public IntPtr Attributes;
                [MarshalAs(UnmanagedType.LPWStr)]
                public string TargetAlias;
                [MarshalAs(UnmanagedType.LPWStr)]
                public string UserName;
            }

Expected behavior

No issue

Actual behavior

S1144 on not used props of Credential struct

Known workarounds

Move struct in class hierarchy:

    partial class WindowsCredentialService
    {
	[StructLayout(LayoutKind.Sequential)]
	internal struct Credential
	{
		public int Flags;
		public int Type;
		[MarshalAs(UnmanagedType.LPWStr)]
		public string TargetName;
		[MarshalAs(UnmanagedType.LPWStr)]
		public string Comment;
		public long LastWritten;
		public int CredentialBlobSize;
		public IntPtr CredentialBlob;
		public int Persist;
		public int AttributeCount;
		public IntPtr Attributes;
		[MarshalAs(UnmanagedType.LPWStr)]
		public string TargetAlias;
		[MarshalAs(UnmanagedType.LPWStr)]
		public string UserName;
	}
		
        class NativeMethods
        {

Related information

• SonarLint for VisualStudio version 8.0.0.92083
• Visual Studio 2022 version 17.9.6
• dotnet version 8

[zsolt-kolbay-sonarsource]

Thank you for reporting this. Confirmed as False Positive.