Attribute targets on unions

[edgarfgp]

Follow up: #17207

Unions compile down to a class or structsharplab.

This PR enforces the new rules on unions.

Old rules

• AttributeTargets.Class
• AttributeTargets.Interface
• AttributeTargets.Delegate
• AttributeTargets.Struct
• AttributeTargets.Enum

New Rules

• AttributeTargets.Class
• AttributeTargets.Struct when using [<Struct>]

Before sharplab

openSystem[<AttributeUsage(AttributeTargets.Class)>]typeClassTargetAttribute()=inherit Attribute()[<AttributeUsage(AttributeTargets.Interface)>]typeInterfaceTargetAttribute()=inherit Attribute()[<AttributeUsage(AttributeTargets.Struct)>]typeStructTargetAttribute()=inherit Attribute()[<InterfaceTarget>]// Does not fail. It should[<StructTarget>]// Does not fail. It should[<ClassTarget>]typeUnion=| Case1
[<InterfaceTarget>]// Does not fail. It should[<StructTarget>]// Does not fail. It should[<ClassTarget>]typeUnion2=| Case1 ofstring*int| Case2 ofstring[<ClassTarget>]// Does not fail. It should[<InterfaceTarget>]// Does not fail. It should[<Struct>]typeStructUnion=| Case1
[<ClassTarget>]// Does not fail. It should[<InterfaceTarget>]// Does not fail. It should[<Struct>]typeStructUnion2=| Case1 ofa:string*int| Case2 ofstring*b:string

After

openSystem[<AttributeUsage(AttributeTargets.Class)>]typeClassTargetAttribute()=inherit Attribute()[<AttributeUsage(AttributeTargets.Interface)>]typeInterfaceTargetAttribute()=inherit Attribute()[<AttributeUsage(AttributeTargets.Struct)>]typeStructTargetAttribute()=inherit Attribute()[<InterfaceTarget>]// Fails as expected[<StructTarget>]// Fails as expected[<ClassTarget>]typeUnion=| Case1
[<InterfaceTarget>]// Fails as expected[<StructTarget>]// Fails as expected[<ClassTarget>]typeUnion2=| Case1 ofstring*int| Case2 ofstring[<ClassTarget>]// Fails as expected[<InterfaceTarget>]// Fails as expected[<Struct>]typeStructUnion=| Case1
[<ClassTarget>]// Fails as expected[<InterfaceTarget>]// Fails as expected[<Struct>]typeStructUnion2=| Case1 ofa:string*int| Case2 ofstring*b:string

Checklist

• Test cases added
• Release notes entry updated

[github-actions]

❗ Release notes required

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/9.0.100.md

[edgarfgp]

This is ready.

[psfinaki]

Yeah I wish we had this proportion of added code and tests in all PRs :D
Thanks Edgar!

[edgarfgp]

Can I get another review please ?

[psfinaki]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[vzarytovskii]

Just a sanity check, type E = A = 1 | B = 2 will still have target enum, right?

[edgarfgp]

Just a sanity check, type E = A = 1 | B = 2 will still have target enum, right?

@vzarytovskii Yes. There are dedicated tests that proves that

[edgarfgp]

Any chance to get this merged before the nullable PR ?

[vzarytovskii]

Any chance to get this merged before the nullable PR ?

Uh oh, I didn't notice the comment before I've pressed merge button, sorry :(

[edgarfgp]

Ok,this is green again

[psfinaki]

Thanks @edgarfgp, merging now :)