Add Swift and Rust custom code pages

[devin-ai-integration]

Add Swift and Rust custom code pages

Summary

Adds "Adding custom code" pages for Swift and Rust SDKs, and updates existing pages that list supported languages to include them. Previously, the custom code documentation covered TypeScript, Python, Go, Java, .NET, PHP, and Ruby — but omitted Swift and Rust despite both having generator sections in the SDK docs.

New files:

• fern/products/sdks/overview/swift/custom-code.mdx — Custom code guide for Swift
• fern/products/sdks/overview/rust/custom-code.mdx — Custom code guide for Rust

Updated files:

• fern/products/sdks/custom-code.mdx — Added Swift and Rust cards to the "Augmenting your SDK with custom code" CardGroup
• fern/products/sdks/sdks.yml — Registered the new pages in the Swift and Rust navigation sections
• fern/products/sdks/reference/generators-yml-reference.mdx — Added missing Rust card to the config reference CardGroup (Swift was already present)

Review & Testing Checklist for Human

• Verify Swift/Rust code examples are idiomatic and match actual generated SDK patterns. The examples were modeled after existing language pages but adapted to Swift/Rust idioms. In particular, the Rust page uses a wrapper struct with Deref (since Rust has no class inheritance) — confirm this is the recommended approach for extending Rust clients.
• Review the Swift custom dependencies section. Unlike Rust (which uses extraDependencies in generators.yml), the Swift page suggests editing Package.swift directly and adding it to .fernignore. Verify whether the Swift generator has a generators.yml config option for dependencies that should be documented instead.
• Check that cards render correctly without icon SVGs. The Swift and Rust cards in custom-code.mdx don't include icon props because no swift-light.svg or rust-light.svg exist in the icons directory. Confirm this renders acceptably or add icons.
• Deploy preview: navigate to the custom code overview page and verify the new cards link correctly to /learn/sdks/generators/swift/custom-code and /learn/sdks/generators/rust/custom-code.

Notes

• Vale linting passed with 0 errors, 0 warnings, and 0 suggestions on all changed files.
• The generators-yml-reference.mdx already had a Swift config card but was missing Rust — this PR adds it.

Link to Devin session: https://app.devin.ai/sessions/7c51ad589c8f4373802fb5c2bed873ab
Requested by: Fern Support

[devin-ai-integration]

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[fern-api]

Requested by: devin
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[github-actions]

🌿 Preview your docs: https://fern-preview-364f8014-880d-4f23-95ab-b526b3482dd1.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/sdks/overview/custom-code
• learn/sdks/generators/rust/custom-code
• learn/sdks/generators/swift/custom-code
• learn/sdks/reference/generators-yml