System.FlagsAttribute no longer appears on any enum types

[DefaultRyan]

The old metadata used to put the flags attribute on enums like DXGI_ADAPTER_FLAG. Now the attribute no longer appears.

This attribute is used by projections to generate bitwise operators for these enums.

[kennykerr]

I just put bitwise operators on any enums with an unsigned underlying type. No attribute needed. 😊

[AArnott]

For .NET we definitely want the [Flags] attribute on those enums for which it makes sense. Analyzers light up based on the presence of that attribute and .NET itself offers some behaviors based on its presence. I think C# makes certain things easier too. Let's please bring it back.

[kennykerr]

Naturally, you'll want the attribute for the C# projection but the metadata doesn't have to include it for you to generate it.

[AArnott]

It does, because I can't assume that all enums should be treated as Flags. Surely some methods accept an enum where only one value should be specified, and the enums that define such values should not define a Flags attribute.

[kennykerr]

I'd love to see such a concrete example. 😉

I'm not saying we shouldn't have an attribute - I'm just not sure it's necessary.

[AArnott]

I'd love to see such a concrete example

Ok, here you go: padding schemes from bcrypt
in C# we use an enum without flags
which is consistent with the docs which describes BCRYPT_PADDING_SCHEMES as:

This data type is a DWORD. This can be one of the following values.

So yes, we certainly have cases where a parameter type can be just one.

Now I'm not sure if this particular case I found would actually be an enum in the header files or the metadata. But the ideal projection as defined by how a hand-written one would be, would define this as a non-Flags enum.

[kennykerr]

Those aren't enums... 😏

By the way, Win32 enums that provide bitwise operators are identified by the DEFINE_ENUM_FLAG_OPERATORS macro (and the resulting operators it defines). If you want to generate the attribute - WHICH IS TOTALLY FINE BY ME 😉 - that's probably the best way to identify them from the source.

[AArnott]

Thanks for the tip, @kennykerr. @sotteson1, can we bring back the attribute based on this hint?

[sotteson1]

@AArnott - yes, any attributes that are flags should be marked appropriately. Since I can't get this automatically from the headers, we will need to add them manually to an input file (the system for this already exists). I'm not sure why it disappeared for DXGI_ADAPTER_FLAG or others but I'll look into it.

[sotteson1]

I'm adding Flags to DXGI_ADAPTER_FLAG and a couple others. I'm going to make the scraper look for DEFINE_ENUM_FLAG_OPERATORS to automatically get more of them.