Make ColumnIndexAttribute bitflags in the ABI

[RReverser]

Description of Changes

As we're adding more variants, it's getting harder to keep track of the "A implies B" relationships between enum variants and to correctly do checks like "is this column autoinc" in different places.

Using bitflags makes expressing those relationships more natural and checking simpler - e.g. you can just do contains(AUTO_INC) as a single bit operation instead of having to remember and list all possible variants that imply autoinc, especially if we're going to add more flags in the future.

Initially I was going to make this change just in C# module generator and convert between ABI enum and bitflags over there, but it seems better to do this at ABI level so it simplifies Rust handling as well.

API

• This is a breaking change to the module API
• This is a breaking change to the ClientAPI

If the API is breaking, please state below what will break

ABI representation of ColumnIndexAttribute (its numeric values) will be different after this change.

[RReverser]

Note to self: this condition is probably incorrect since intersection will also catch INDEXED bit, needs to remove it before checking.

[Centril]

Suggested change

	const UNSET = Self::empty().bits();
	/// Index no unique
	const INDEXED = 0b0001;
	/// Generate the next [Sequence]
	const AUTO_INC = 0b0010;
	/// Index unique
	const UNIQUE = Self::INDEXED.bits() | 0b0100;
	/// Unique + AutoInc
	const IDENTITY = Self::UNIQUE.bits() | Self::AUTO_INC.bits();
	/// Primary key column (implies Unique)
	const PRIMARY_KEY = Self::UNIQUE.bits() | 0b1000;
	/// PrimaryKey + AutoInc
	const PRIMARY_KEY_AUTO = Self::PRIMARY_KEY.bits() | Self::AUTO_INC.bits();
	/// No attributes / flags set.
	const UNSET = Self::empty().bits();
	/// Indexed but not unique.
	const INDEXED = 0b0001;
	/// Generate the next [Sequence].
	const AUTO_INC = 0b0010;
	/// Indexed + unique.
	const UNIQUE = Self::INDEXED.bits() | 0b0100;
	/// Unique + AutoInc.
	const IDENTITY = Self::UNIQUE.bits() | Self::AUTO_INC.bits();
	/// Primary key column (implies Unique).
	const PRIMARY_KEY = Self::UNIQUE.bits() | 0b1000;
	/// PrimaryKey + AutoInc
	const PRIMARY_KEY_AUTO = Self::PRIMARY_KEY.bits() | Self::AUTO_INC.bits();

[Centril]

Nice!

[Centril]

Consider extracting out bits like this to methods / functions since the current one is getting rather large.

[RReverser]

Yeah fwiw ideally I'd just use iter_names of bitflags here, but it has a quirk where it deduplicates bitflags only if the larger ones (those that encompass others) come first.

I changed the definition of struct at first but figured it's more obvious/maintainable to just write out the names explicitly.

[Centril]

Yep, extra crate would be good.