Allow object expression without overrides

[edgarfgp]

Description

Add support for object expression without overrides.

Before

To create an object expression without overrides, the user has to override a member, even if it is not necessary.

typeIFirst=interfaceend[<AbstractClass>]typeClassEnd()=classend// FS0738 Invalid object expression. Objects without overrides or interfaces should use the expression form 'new Type(args)' without braces.letobjExpr={new ClassEnd()}// Workaround: override a member like ToString, Equals, GetHashCode, etc.letobjExpr={new ClassEnd()withmemberthis.ToString()="ClassEnd"}// Workaround: implement a marker interfaceletobjExpr={new ClassEnd()interface IFirst }typeClass()=classend//FS0738 Invalid object expression. Objects without overrides or interfaces should use the expression form 'new Type(args)' without braces.letobjExpr={new Class()}// Workaround: override a member like ToString, Equals, GetHashCode, etc.letobjExpr={new Class()withmemberthis.ToString()="ClassEnd"}// Workaround: implement a marker interfaceletobjExpr={new Class()interface IFirst }

After

We won't need to use any workaround to use classes(abstract or non-abstract) in object expressions.

[<AbstractClass>]typeAbstractClass()=classend// OkletobjExpr={new AbstractClass()}typeClass()=classend// OkletobjExpr={new Class()}

• Language suggestion: Allow object expression without overrides fsharp/fslang-suggestions#632
• RFC: (Allow object expression without overrides. fsharp/fslang-design#785)
• RFC discussion: F# RFC FS-632 - Allow object expression without overrides fsharp/fslang-design#781

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
LanguageFeatures.fsi	docs/release-notes/.Language/preview.md

[vzarytovskii]

Can be merged after RFC is approved by Don

[psfinaki]

Fabulous work. Thanks for adding tests for the old versions as well. Great stuff Edgar!