Fix generated error constructors and constraint attributes using the wrong C# types

[Timothee Guerin (timotheeguerin)]

The emitter had three separate TypeSpec-scalar-to-C#-type-name maps, and they disagreed. Properties were rendered from one, error-model constructor parameters from another, and constraint attribute type arguments from a third — so the generated code did not compile:

@error model ValidationError {
  occurredAt: utcDateTime;
  docs: url;
  severity: int8;
}

  public partial class ValidationError : HttpServiceException
  {
      public required DateTimeOffset OccurredAt { get; set; }
      public required string Docs { get; set; }
      public required SByte Severity { get; set; }

-     public ValidationError(DateTimeOffset occurredAt, Uri docs, sbyte severity)
+     public ValidationError(DateTimeOffset occurredAt, string docs, SByte severity)

NumericConstraint<T> had the same problem — the attribute was instantiated with a different type than the property it annotated, so it failed to bind.

The three maps collapse into one scalar-overrides.ts that layers the emitter's deliberate divergences (plainDate/plainTime → DateTime, url → string, safeint → long, CLR names for sized integers) over the emitter framework defaults. Anywhere a C# type name is needed outside a rendering context now goes through it, so it cannot drift from what TypeExpression renders again.

---

Part of a 7-PR stack moving @typespec/http-server-csharp onto the emitter framework. Stacked on #11599 — only the last commit is new here.

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commit: c73ec36

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All changed packages have been documented.

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

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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,> ),,> });,>

@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.

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