Build models, properties and enums on the emitter framework

[Timothee Guerin (timotheeguerin)]

The emitter shipped private forks of the framework's ClassDeclaration, Property and EnumDeclaration — copies made because the framework offered no way to adjust them, which then drifted. With declaration overrides and component props now available (#11597, #11598), the forks go away and the divergences are expressed as configuration:

• The property policy (nullability, virtual/override/new, error-model members, JSON attributes) becomes a registered ModelProperty declaration override.
• ServerClassDeclaration becomes EfClassDeclaration with an explicit properties list and the generated constructors passed as children.
• Enums renders through EfEnumDeclaration with an explicit members list, keeping the emitter's more permissive union-as-enum detection.

models.tsx drops from ~270 lines to ~125, and the whole change is a net -350 lines.

One structural note for reviewers: the framework's TypeExpression recurses into itself, not into a consumer's wrapper. Any type kind whose handling recurses into a contained type therefore has to stay in the emitter's wrapper or its divergences are silently lost for the nested type. Scalars are the exception — they go through component overrides, which apply at every level. This is now written down in a comment at the top of the wrapper, because it is not obvious and it caused a regression while writing this.

Generated output is unchanged.

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Part of a 7-PR stack moving @typespec/http-server-csharp onto the emitter framework. Stacked on #11600 — only the last commit is new here.

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commit: 1befaa3

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All changed packages have been documented.

• ✅ @typespec/emitter-framework
• ✅ @typespec/http-server-csharp

Show changes

@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,> ),,> });,>

@typespec/http-server-csharp - internal ✏️

Use Alloy's C# keyword handling and System.Text.Json symbols instead of local copies,> ,> Deletes the emitter's own 217-line C# keyword table and its re-declaration of the System.Text.Json.Serialization attributes, which are both provided by @alloy-js/csharp. Namespace segments that collide with common BCL type names are still renamed, now in a dedicated getCSharpNamespaceName helper.

@typespec/http-server-csharp - fix ✏️

Fix generated error model constructors and numeric constraint attributes using the wrong C# types,> ,> Error model constructors declared parameters such as DateOnly, Uri and sbyte while the matching properties were DateTime, string and SByte, producing code that did not compile. NumericConstraintAttribute<T> had the same mismatch, which stopped the converter from binding.

@typespec/http-server-csharp - internal ✏️

Build model, property and enum generation on @typespec/emitter-framework components,> ,> The emitter carried private forks of the framework's ClassDeclaration, Property and EnumDeclaration. They are now consumed directly, with the emitter's own behavior expressed as a declaration override and component props. Generated output is unchanged.

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