casting interface + null-conditional == uncompilable

[Hefaistos68]

Decompiled PaintDotNet.Core.dll from the Paint.Net app (getpaint.net) which leaves me with two issues: here is the first one, the other one is a call into a base method that doesnt exist, but actually should be a call into a ctor in the base.

This is not valid code:

	((schema as IObjectRef)?)?.Dispose();
	((id as IObjectRef)?)?.Dispose();
	((value as IObjectRef)?)?.Dispose();

Input code

The IL code in question:

	.method family hidebysig virtual 
		instance void Dispose (
			bool disposing
		) cil managed 
	{
		// Method begins at RVA 0x2a300
		// Code size 104 (0x68)
		.maxstack 2
		.locals init (
			[0] class [PaintDotNet.Base]PaintDotNet.ComponentModel.IObjectRef schemaRef,
			[1] class [PaintDotNet.Base]PaintDotNet.ComponentModel.IObjectRef idRef,
			[2] class [PaintDotNet.Base]PaintDotNet.ComponentModel.IObjectRef valueRef
		)

		// sequence point: (line 46, col 13) to (line 46, col 27) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_0000: ldarg.1
		IL_0001: brfalse.s IL_004b

		// sequence point: (line 48, col 17) to (line 48, col 57) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_0003: ldarg.0
		IL_0004: ldfld object PaintDotNet.Imaging.MetadataItem::schema
		IL_0009: isinst [PaintDotNet.Base]PaintDotNet.ComponentModel.IObjectRef
		IL_000e: stloc.0
		IL_000f: ldloc.0
		IL_0010: brfalse.s IL_001b

		// sequence point: (line 50, col 21) to (line 50, col 42) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_0012: ldloc.0
		IL_0013: brfalse.s IL_001b

		IL_0015: ldloc.0
		IL_0016: callvirt instance void [mscorlib]System.IDisposable::Dispose()

		// sequence point: (line 53, col 17) to (line 53, col 49) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_001b: ldarg.0
		IL_001c: ldfld object PaintDotNet.Imaging.MetadataItem::id
		IL_0021: isinst [PaintDotNet.Base]PaintDotNet.ComponentModel.IObjectRef
		IL_0026: stloc.1
		IL_0027: ldloc.1
		IL_0028: brfalse.s IL_0033

		// sequence point: (line 55, col 21) to (line 55, col 38) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_002a: ldloc.1
		IL_002b: brfalse.s IL_0033

		IL_002d: ldloc.1
		IL_002e: callvirt instance void [mscorlib]System.IDisposable::Dispose()

		// sequence point: (line 58, col 17) to (line 58, col 55) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_0033: ldarg.0
		IL_0034: ldfld object PaintDotNet.Imaging.MetadataItem::'value'
		IL_0039: isinst [PaintDotNet.Base]PaintDotNet.ComponentModel.IObjectRef
		IL_003e: stloc.2
		IL_003f: ldloc.2
		IL_0040: brfalse.s IL_004b

		// sequence point: (line 60, col 21) to (line 60, col 41) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_0042: ldloc.2
		IL_0043: brfalse.s IL_004b

		IL_0045: ldloc.2
		IL_0046: callvirt instance void [mscorlib]System.IDisposable::Dispose()

		// sequence point: (line 64, col 13) to (line 64, col 32) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_004b: ldarg.0
		IL_004c: ldnull
		IL_004d: stfld object PaintDotNet.Imaging.MetadataItem::schema
		// sequence point: (line 65, col 13) to (line 65, col 28) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_0052: ldarg.0
		IL_0053: ldnull
		IL_0054: stfld object PaintDotNet.Imaging.MetadataItem::id
		// sequence point: (line 66, col 13) to (line 66, col 31) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_0059: ldarg.0
		IL_005a: ldnull
		IL_005b: stfld object PaintDotNet.Imaging.MetadataItem::'value'
		// sequence point: (line 68, col 13) to (line 68, col 37) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_0060: ldarg.0
		IL_0061: ldarg.1
		IL_0062: call instance void [PaintDotNet.Base]PaintDotNet.Disposable::Dispose(bool)
		// sequence point: (line 69, col 9) to (line 69, col 10) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
		IL_0067: ret
	} // end of method MetadataItem::Dispose

Erroneous output

	protected override void Dispose(bool disposing)
	{
		if (disposing)
		{
			((schema as IObjectRef)?)?.Dispose();
			((id as IObjectRef)?)?.Dispose();
			((value as IObjectRef)?)?.Dispose();
		}
		schema = null;
		id = null;
		value = null;
		base.Dispose(disposing);
	}

Details

• Product in use: ILSpy VS extension
• Version in use: ILSpy version 6.2.1.6137
  decompilation for C# 8.0,

[siegfriedpammer]

When selecting C# 5.0, the output looks like this:

protected override void Dispose(bool disposing)
{
	if (disposing)
	{
		IObjectRef schemaRef = schema as IObjectRef;
		if (schemaRef != null && schemaRef != null)
		{
			schemaRef.Dispose();
		}
		IObjectRef idRef = id as IObjectRef;
		if (idRef != null && idRef != null)
		{
			idRef.Dispose();
		}
		IObjectRef valueRef = value as IObjectRef;
		if (valueRef != null && valueRef != null)
		{
			valueRef.Dispose();
		}
	}
	schema = null;
	id = null;
	value = null;
	base.Dispose(disposing);
}

The problem seems to be the duplication of br.false instructions such as:

	IL_000f: ldloc.0
	IL_0010: brfalse.s IL_001b

	// sequence point: (line 50, col 21) to (line 50, col 42) in D:\src\pdn\src\Core\Imaging\MetadataItem.cs
	IL_0012: ldloc.0
	IL_0013: brfalse.s IL_001b

No idea, why or how this code was generated. For the null conditional operator, we should probably implement some simplification transform, e. g., expr??.member => expr?.member.