AttributeTargets better error message

[edgarfgp]

Description

BEFORE

We had one message to fit all the invalid attribute targets messages.

This attribute is not valid for use on this language element

AFTER

We have now: This attribute cannot be applied to (<one or more targets>). Valid targets are: (<one or more targets>) e.g.

• This attribute cannot be applied to struct. Valid targets are: class
• This attribute cannot be applied to property, field, return value. Valid targets are: method
• This attribute cannot be applied to class. Valid targets are: interface
• This attribute cannot be applied to method, property. Valid targets are: field

For cases here F# does not support attributes or still not a valid analysis for attribute targets that we want to enforce. We will still fallback to This attribute is not valid for use on this language element.

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/10.0.100.md

[T-Gro]

Why is the current target an array and not a single element? That part I find confusing in the error message.

[edgarfgp]

So:

• currentTarget represents the specific targets that the compiler wants to enforce e.g. let FieldDecl = AttributeTargets.Field ||| AttributeTargets.Property hence the reason been a list.
• validTargets all the targets defined in the attribute declaration.

Alternatively we an maybe pass through the type of declaration where this attribute is been used as string. like "functions" etc. But this will differ from what the AttributeTargets naming is using.

[T-Gro]

Are the currentTargets a "and" or "or" combination?
i.e. do all of them have to be met, or just one?

(I would like that to be apparent from the naming if possible, also then in the resolution of the error message)

[edgarfgp]

@T-Gro This is an OR . What about something like e.g. Invalid attribute target. Expected: class, struct, parameter. Actual: method, property, field, return value.