Dispatch declaration overrides in Experimental_ComponentOverrides

[Timothee Guerin (timotheeguerin)]

An override descriptor already accepted a declaration entry, but nothing ever dispatched to it — only reference was wired up. So an emitter could change how a type is referenced and had no say in how it is declared. The only way to customize a declaration was to copy the framework component into your own package and diverge from it, which is exactly what @typespec/http-server-csharp did for classes, properties and enums.

Experimental_OverridableComponent now dispatches declaration too, and the C# ClassDeclaration, Property and EnumDeclaration render through it. An override can replace the declaration outright, or re-render the default with different props:

const overrides = Experimental_ComponentOverridesConfig().forTypeKind("ModelProperty", {
  declaration: (props) =>
    isSecret(props.type) ? (
      <props.Declaration {...props.declarationProps} public={false} internal />
    ) : (
      props.default
    ),
});

props.Declaration is the unwrapped body, so re-rendering it does not recurse back through the override.

The declaration props type is generic and defaults to Record<string, any>, because the existing Experimental_CustomTypeToProps map is TypeScript-specific (VarDeclarationProps, ObjectPropertyProps) and means nothing for C#. Callers that want type safety pass the concrete props type: .forTypeKind<"ModelProperty", PropertyProps>(...).

---

Part of a 7-PR stack moving @typespec/http-server-csharp onto the emitter framework. Stacked on #11596 — only the last commit is new here.

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commit: e806960

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• ✅ @typespec/emitter-framework

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@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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