Suggest to reverse condition when 'Then' block is empty

[retailcoder]

This code:

If foo = 42 Then Else DoSomething

Should be rewritten as:

If Not (foo = 42) Then DoSomething

Or better:

If foo <> 42 Then DoSomething

But reversing operators might not be trivial in all condition expressions.

Also applies to if blocks:

If foo  = 42 Then
Else
    DoSomething
End If

Should be rewritten as:

If Not (foo = 42) Then
    DoSomething
End If

[Vogel612]

This might be interesting with more complex if-conditions...

If foo < CONST and bar <> 545 or baz = 25 Then Else DoSomething

[Hosch250]

I handled this for C# code in VSDiagnostics. I should be able to handle it for VBE code too.

[retailcoder]

@Hosch250 does VSD revert the operators, or simply sticks a ! in front of the existing condition? I don't mind either, but it sure makes a smarter ducky if we actually revert the operators (correctly accounting for operator precedence and parentheses... doesn't look simple)

[Hosch250]

It actually reverts the operators:

!= becomes ==
== becomes !=
> becomes <=
<= becomes >
< becomes >=
>= becomes <
!(condition) becomes (condition)
(condition) becomes !(condition)
&& becomes ||
|| becomes &&

[retailcoder]

Ok, so

<> becomes =
= becomes <>
> becomes <=
<= becomes >
< becomes >=
>= becomes <
Not {condition} becomes {condition}
{condition} becomes Not {condition}
And becomes Or
Or becomes And

What of XOr? Also, keep in mind that C# logical operators short-circuit; not VBA's.

[Hosch250]

This will definitely be a mite trickier than VSD because Roslyn has that nifty tree defining precedence and stuff, but not impossible. It will be a little like parsing a mathematical expression, which I have done before. Also, I think XOr stays the same, but I can't say for sure.

[Vogel612]

"A XOr B" is basically "(A and not B) or (not A and B)", inverting those is a little trickier...

[Hosch250]

A And Not B inverted makes Not A Or B

[ThunderFrame]

Need to consider reversing these too:

If obj Is Nothing Then
If Not obj Is Nothing

If IsArray(aData) Then
If Not IsArray(aData) Then

[ThunderFrame]

Might need to apply the same functionality to Compile Directives.

[Hosch250]

Other than the code to figure out which operator needs to be inverted (only the top-level one does), this is easily doable with the rewriters at this point. Basically, this would be a parse tree inspection that checked for empty if blocks with non-empty else blocks.

A similar inspection would be an if block that was empty and either no else or an empty else. If there was a non-empty Else If block, then it would just remove the if and the else before the next if and leave everything else.