Copilot/add expression decorations

[johanste]

Decorating expressions

Decorators can be applied to inline model expressions and other type expressions used in property types, aliases, and is/extends clauses. Place the decorator before the expression:

model Pet {
  owner: @doc("Owner contact info") {
    name: string;
    phone: string;
  };
}
alias Address = @doc("A mailing address") {
  street: string;
  city: string;
};

[github-actions]

All changed packages have been documented.

• ✅ @typespec/compiler

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@typespec/compiler - feature ✏️

Add support for decorating type expressions. Decorators can now be applied to inline models, type references, union expressions, and is/extends targets.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/microsoft/typespec/@typespec/compiler@9747

commit: 0c8359a

[azure-sdk]

You can try these changes here

🛝 Playground	🌐 Website	🛝 VSCode Extension

[witemple-msft]

I think it is potentially a big problem to allow decorating type references. The implementation in this PR will allow you to overwrite metadata without controlling the original declaration.

https://cadlplayground.z22.web.core.windows.net/prs/9747/?e=%40typespec%2Fopenapi3&c=QGRvYygiMSIpCm1vZGVsIFgge30KxwxZIHsKICB4OiDGJTIiKSBYOwp9&options=%7B%7D&vs=%7B%7D

It seems like we only want to allow decorating type literals, i.e. expressions that create unique instances of a Type.

I'm also a little concerned about the union case. We have potentially a lot of code that assumes that a union can only be decorated if it is a named declaration. We do not even allow augmentations like:

alias A = string | int32;

@@doc(A, "Example");
      ~ > error augment-decorator-target: Cannot augment union expressions.

If the other PR allowing named model expressions lands, then I would support allowing decorating type expressions that start with a keyword: @doc("Example") model { ... }, @dec union { string, int32 }, etc.

[timotheeguerin]

yeah we did talk about this might be the only way to allow inline decorator was when using the keyword form of expressions. I also feel like from a quick look that while it does seem to pass the test I don't think copilot really did the change correctly, I don't think we need a new Decorator node in the tree