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This is ready

Thanks for the fix, tests and refactoring. That's a good one.

I wonder if we should add some notes to some docs about it. This is a technically correct behavior but might seem unintuitive to F# newcomers.

Im planning to submit a RFC with the AttributeTargets rules once Im done with #13526 to make it clear

Awesome :)

This PR should merged before #16790. Thanks

@dotnet/fsharp-team-msft

UnionCase compiles down to a static Method so should only enforce AttributeTargets.Method SharpLab

Thought it's a breaking change, I think it's fine from the the "correctness" point of view, however having AttributeTargets.Method working feels weird, since DU constructors being "methods" in the IL is an implementation detail in F# (not in C#).

If something is using generated attributes, they can be "correctly" utilised in C#, but not in F#, since from F# standpoint, New* methods are nonexistent, and cases are treated as constructors, if that makes sense.

That said, I don't mind merging it as it is now, but it still feels weird to me that we allow Method and not Constructor.

That said, I don't mind merging it as it is now, but it still feels weird to me that we allow Method and not Constructor.

@vzarytovskii As you know there not an actual spec yet for this, so if Constructor make sense from the F# perspective we can add it

UnionCase compiles down to a static Method

This is not always the case. There's no single direct mapping between union cases and their compiled .NET representations: depending on the union and its union cases, they compile to different things (nested classes, properties, constructor methods, case test properties, nested Tags enum and so on).

For example, these union cases compile to properties, not methods:

type U =
    | A
    | B

I don't see any tests covering these cases.

Is there an RFC for this?

UnionCase compiles down to a static Method

This is not always the case. There's no single direct mapping between union cases and their compiled .NET representations: depending on the union and its union cases, they compile to different things (nested classes, properties, constructor methods, case test properties, nested Tags enum and so on).

For example, these union cases compile to properties, not methods:

type U =
    | A
    | B

I don't see any tests covering these cases.

Is there an RFC for this?

@auduchinok No Yet. Im going through the issues and figuring out which AttributeTargets should be enforced. Will create a RFC at some point as soon I have a clear picture of this.

This is not always the case. There's no single direct mapping between union cases and their compiled .NET representations: depending on the union and its union cases, they compile to different things (nested classes, properties, constructor methods, case test properties, nested Tags enum and so on).

I will look into this as create a PR with tests