F# under the covers XII -- Reflector 6.0 decompilation to C#

A new Reflector release (6.0.0.918), and time to see whether it can approximate in C# some compiled F# code that the 5.1.6.0 version balked at.

The generated IEquatable.Compare method that couldn't be handled before now succeeds -- the section that had problems now resolves to

	public sealed override bool Equals(Context obj)
	{
	if (this <= null)
	{
	return (obj <= null);
	}
	if (obj <= null)
	{
	return false;
	}

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and it's not surprising that comparing not-greater-than-null might be an unexpected piece of IL.

However, when there is a problem with decompilation, the new version no longer provides the detail of which instruction it didn't like. So I don't know why this

	let (|CSharpConstStub|_|) (fn:Method) =
	if fn.Name.ToString() @ "get_" then None
	else match MapToTypes fn.Body.Statements with
	| [NodeType.Block; NodeType.Block] ->
	let block1 = fn.Body.Statements.[0] :?> Block
	let block2 = fn.Body.Statements.[1] :?> Block
	match (MapToTypes block1.Statements, MapToTypes block2.Statements) with
	| ( [NodeType.Nop; NodeType.AssignmentStatement; NodeType.Branch], [NodeType.Return]) ->
	let ass = block1.Statements.[1] :?> AssignmentStatement
	let branch = block1.Statements.[2] :?> Branch
	if branch.Target <> block2 || null <> branch.Condition then None
	elif ass.Source.NodeType <> NodeType.MemberBinding && ass.Source.NodeType <> NodeType.Literal then None
	else match (block2.Statements.[0], ass.Target) with
	| ReturnTemp -> Some()
	| _ -> None
	| _ -> None
	| _ -> None

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raises an error report when trying to decompile to C# (or MC++ or VB); or why this

	let (|CSharpGetterInterior|_|) (state:(Statement * Statement * Member)) =
	let (a, b, fn) = state
	let block = a :?> Block
	let block2 = b :?> Block
	match MapToTypes block.Statements with
	| [NodeType.Nop; NodeType.AssignmentStatement; NodeType.Branch] ->
	let ass = block.Statements.[1] :?> AssignmentStatement
	let branch = block.Statements.[2] :?> Branch
	if (ass.Source.NodeType <> NodeType.MemberBinding ||
	null <> branch.Condition ||
	branch.Target <> block2) then None
	elif block2.Statements.Count <> 1 then None
	else match (block2.Statements.[0], ass.Target) with
	| ReturnTemp ->
	let n = (ass.Source :?> MemberBinding).BoundMember.Name.ToString()
	if fn.Name.ToString().ToUpperInvariant() <> ("get_" + n).ToUpperInvariant() then None
	else Some ()
	| _ -> None
	| _ -> None

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throws a NullPointerException while trying to report an error when asked to decompile it as C# (I was able to get an error report sent when asking for VB instead).

Dropping back to 5.1.6.0, both show the usual "invalid branching condition", and point to

if branch.Target <> block2 || null <> branch.Condition then None

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(the former condition) and

if (ass.Source.NodeType <> NodeType.MemberBinding ||

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respectively, on the path where we are short-circuiting, as in

	L_020d: call bool [FSharp.Core]Microsoft.FSharp.Core.LanguagePrimitives/HashCompare::GenericEqualityIntrinsic<class [Microsoft.Cci]Microsoft.FxCop.Sdk.Block>(!!0, !!0)
	L_0212: ldc.i4.0
	L_0213: ceq
	L_0215: brfalse.s L_0219
	L_0217: br.s L_021b
	L_0219: br.s L_021f
	L_021b: ldc.i4.1
	L_021c: nop
	L_021d: br.s L_0238

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where the last line here is the one that the decompilation faults on.