Make the C# declaration components authorable

[Timothee Guerin (timotheeguerin)]

The C# declaration components rendered exactly one shape and dropped anything the caller passed. ClassDeclaration always emitted every property of the model and nothing else, Property accepted three props out of the ~15 Alloy supports, EnumDeclaration always derived its members from the type, and JsonConverter had a fixed body with no way to document it or change its visibility. An emitter that needed a constructor in the class, or a filtered property list, or a differently-named property, had to fork the component.

They now take props:

<ClassDeclaration type={model} properties={visibleProperties} partial>
  <Constructor />
</ClassDeclaration>

• ClassDeclaration — explicit properties list, extra members as children.
• Property — the full Alloy property prop set, plus name and csharpType overrides.
• EnumDeclaration — explicit members list and a jsonAttributes prop.
• JsonConverter — doc, access modifiers, extra members, an explicit csharpType, and a readReturns override.

Caller-supplied props are spread last so they win over the framework defaults, and every prop is optional, so existing behavior is unchanged.

---

Part of a 7-PR stack moving @typespec/http-server-csharp onto the emitter framework. Stacked on #11597 — only the last commit is new here.

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commit: 387a153

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All changed packages have been documented.

• ✅ @typespec/emitter-framework

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@typespec/emitter-framework - feature ✏️

Let emitters author the C# declaration components instead of forking them,> ,> - ClassDeclaration accepts an explicit properties list and extra members as children.,> - Property accepts every Alloy property prop, plus name and csharpType overrides.,> - EnumDeclaration accepts an explicit members list and a jsonAttributes prop.,> - JsonConverter accepts doc, access modifiers, extra members, an explicit csharpType, and a readReturns override.,> ,> tsx,> <ClassDeclaration type={model} properties={model.properties.values().filter(isVisible)} partial>,> <Constructor />,> </ClassDeclaration>,>

@typespec/emitter-framework - fix ✏️

Make the C# TypeExpression handle every type kind instead of throwing,> ,> Tuple, StringTemplate, EnumMember, ModelProperty, UnionVariant, template parameters and the full Intrinsic set are now supported, and an unsupported type reports a diagnostic and falls back to object rather than throwing. Also fixes the C# components reporting a TypeScript diagnostic for unsupported scalars, and corrects the C# expressions for the null and never intrinsics.

@typespec/emitter-framework - feature ✏️

Support declaration overrides in Experimental_ComponentOverrides,> ,> Only reference overrides were dispatched, so an emitter could customize how a type is referenced but not how it is declared, forcing it to fork the framework's declaration components. The C# ClassDeclaration, Property and EnumDeclaration now render through the override point.,> ,> tsx,> const overrides = Experimental_ComponentOverridesConfig().forTypeKind("ModelProperty", {,> declaration: (props) =>,> props.type.name === "id" ? (,> <props.Declaration {...props.declarationProps} name="Identifier" />,> ) : (,> props.default,> ),,> });,>

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