[TCGC] Add InitializedBy.none to support omitting generated client constructors

[Copilot]

Plan to add None to InitializedBy enum

• Explore repository structure and understand the codebase
• Add None value (0) to InitializedBy enum in lib/decorators.tsp
• Update InitializedByFlags enum in src/interfaces.ts to include None = 0 and change Default = -1
• Update validation logic in src/decorators.ts to accept value 0 for None
• Fix falsy check in src/clients.ts to use !== undefined instead of truthy check
• Add validation bypass for None in client type validation
• Add tests for the new None initialization type
• Build the package and verify changes
• Run tests to ensure everything works correctly
• Add changelog entry
• Address code review feedback with improved documentation
• Format code using prettier
• Regenerate changeset using pnpm -w change add command

Original prompt

---

This section details on the original issue you should resolve

<issue_title>tcgc: add None to InitializedBy enum</issue_title>
<issue_description>### Clear and concise description of the problem

There is an uncommon need (storage needs it) to indicate that client constructors should be omitted (i.e. they will be hand-written for some reason). Please add None to the InitializedBy enum passed to ClientInitializationOptions so tsp authors can express this.

Checklist

• Follow our Code of Conduct
• Check that this issue is about the Azure libraries for typespec. For feature request in the typespec language or core libraries file it in the TypeSpec repo
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.</issue_description>

Comments on the Issue (you are @copilot in this section)

@vincenttran-msft Slight nit: It would be preferable if we could disable constructors but still get the generated options bag. This is mostly to remove the necessity to do a hand-edit to update the default `version` that ships, when that really should come straight from the generated code.

/// Options used when creating a `BlobClient`
#[derive(Clone, SafeDebug)]
pub struct BlobClientOptions {
    /// Allows customization of the client.
    pub client_options: ClientOptions,
    /// Specifies the version of the operation to use for this request.
    pub version: String,
}

impl Default for BlobClientOptions {
    fn default() -> Self {
        Self {
            client_options: ClientOptions::default(),
            version: String::from("2026-04-06"),
        }
    }
}
```</body></comment_new>
</comments>

• Fixes tcgc: add None to InitializedBy enum #3859

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[tadelesh]

@copilot Use pnpm -w format to format the code and use pnpm -w change add to add changeset.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/Azure/typespec-azure/@azure-tools/typespec-client-generator-core@3877

commit: 6c81af8

[Copilot]

@copilot Use pnpm -w format to format the code and use pnpm -w change add to add changeset.

Done! Code formatted and changeset regenerated. See commit 0e726db.

[azure-sdk]

All changed packages have been documented.

• ✅ @azure-tools/typespec-client-generator-core

Show changes

@azure-tools/typespec-client-generator-core - feature ✏️

Added InitializedBy.none (value 0) to allow TypeSpec authors to indicate that client constructors should be omitted and hand-written. Note: The internal InitializedByFlags.Default value changed from 0 to -1 to accommodate this addition.

[azure-sdk]

You can try these changes here

🛝 Playground	🌐 Website