[Mpdreamz]

A survey of C# 12–14 features, read through the reader, the writer, the parser and the Roslyn oracle, found three things written wrong:

• Operators. C# 14 compound assignment operators (void operator +=(Money other), %=, >>>= and the rest), the instance void operator ++() and --, their checked forms, and explicit operator checked int came out under their metadata names, such as op_CheckedAdditionAssignment. The parser reads them all back; a ++ without a parameter is the instance one.
• Readonly struct members. Every auto-property getter in a struct is readonly, so int X { get; set; } was written readonly int X { readonly get; set; }. Property-level readonly now means what C# means by it: every accessor is readonly, which C# writes on the property. A readonly set was not read at all.
• Params spans. params ReadOnlySpan<string> parts was written scoped params ReadOnlySpan<string>, which C# rejects (CS9350). A params span is scoped without saying so; the reader leaves that implied scoped out, and the writer puts params first if a model has both.

The rest of the survey reads right, matches Roslyn and round-trips: params collections, allows ref struct, [Experimental], [OverloadResolutionPriority], InlineArray, ref structs implementing interfaces, partial properties and events, field-backed properties, primary constructors, ref readonly parameters, record structs and static abstract/virtual interface members. They are now all in the new modern writer sample.

Verified:

• The oracle now checks readonly on methods and accessors, for structs that are not readonly.
• All properties pass, and mise run ci is green locally.
• Mutations caught:
  • property readonly taken from the getter alone fails the framework round trips and the generated libraries;
  • parsing ++ as always static fails the model round trip;
  • keeping the implied scoped fails the oracle on CoreLib, System.Text.Json and System.Collections.Immutable.

🤖 Generated with Claude Code