[Bug]: @madeRequired breaks OptionalProperties

[mbarnes]

Describe the bug

Corner case follow-up to #441.

When using the OptionalProperties template on a model that includes a @madeRequired decorator, the decorator is preserved in the generated model which causes a compiler error.

Compiling the reproducer below results in:

TypeSpec compiler v1.13.0

× Compiling
Diagnostics were reported during compilation:

main.tsp:12:3 - error @typespec/versioning/made-required-optional: Property 'foo?' marked with @madeRequired but is optional. Should be 'foo'
> 12 |   foo: string
     |   ^^^

Found 1 error.

I think OptionalProperties should omit @madeRequired decorators in the generated model.

Reproduction

import "@typespec/versioning";

@TypeSpec.Versioning.versioned(Reproducer.Versions)
namespace Reproducer;

enum Versions {
  demo: "demo"
}

model Required {
  @TypeSpec.Versioning.madeRequired(Versions.demo)
  foo: string
}

model Optional is OptionalProperties<Required>;

Checklist

• Follow our Code of Conduct
• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• The provided reproduction is a minimal reproducible example of the bug.

[github-actions]

🎯 Issue Triage

When applying OptionalProperties<T> to a model whose properties use @madeRequired, the decorator is preserved in the generated model, causing a compiler error because the property is now optional but still marked as required.

Category: Bug
Area: lib:versioning

🔗 [Playground Reproduction]((typespec.io/redacted)

📋 Reproduction code

import "`@typespec/versioning`";

`@TypeSpec`.Versioning.versioned(Reproducer.Versions)
namespace Reproducer;

enum Versions {
  demo: "demo"
}

model Required {
  `@TypeSpec`.Versioning.madeRequired(Versions.demo)
  foo: string
}

model Optional is OptionalProperties<Required>;

🔍 Analysis

• OptionalProperties<T> makes all properties optional by mapping them, but currently preserves all decorators including @madeRequired.
• The @madeRequired decorator asserts that the property must be required (i.e., not optional), which conflicts with what OptionalProperties does.
• The fix should be in OptionalProperties (or the versioning library's decorator validation) to strip @madeRequired when properties are made optional through this template.
• This is a follow-up to PR Fix: Spreading versioned models #441 which introduced OptionalProperties.

📝 Suggested next steps

• Investigate OptionalProperties implementation to see where decorators are copied to the generated model
• Determine whether @madeRequired should be stripped in OptionalProperties, or whether the @madeRequired validator should skip properties in mapped types
• Add a test case covering OptionalProperties with @madeRequired-annotated properties

Generated by Agentic Triage

[iscai-msft]

assigning to Mark Cowlishaw (@markcowl) and Timothee Guerin (@timotheeguerin) who are on vacation, they will take a look at this when they're back in 2 weeks. Are you blocked by this or is it an existing corner case that you are highlighting?

[mbarnes]

No I'm not blocked by this. Encountered it while trying out some TypeSpec workarounds for other issues. I've moved on but just wanted to call your attention to it.