Sym.node and Sym.declarations is not defined correctly

[RodgeFu]

The definition of Sym.node and Sym.declarations is incorrect, undefined is missed when it's possible, which makes compiler not able to help to do type check and potentially hide some bug when undefined is not handled properly.

Look at the createSymbol() method as below, you can find it accept undefined as node, but the returned Sym.node and Sym.declarations are defined as Node and Node[] only
https://github.com/RodgeFu/typespec/blob/550377179c4173aa27a91605b367d65df17f696f/packages/compiler/src/core/binder.ts#L669
And following is an example when undefined is passed in as node: https://github.com/RodgeFu/typespec/blob/550377179c4173aa27a91605b367d65df17f696f/packages/compiler/src/core/name-resolver.ts#L189
Also this behavior impacts other functions returning Sym.Node/Declaration to miss undefined in the return type, like https://github.com/RodgeFu/typespec/blob/550377179c4173aa27a91605b367d65df17f696f/packages/compiler/src/core/binder.ts#L708

[github-actions]

🎯 Issue Triage

The Sym.node and Sym.declarations fields are typed as Node and Node[] respectively, but createSymbol() accepts undefined as node, meaning undefined can be present at runtime without type-level visibility — potentially hiding null-dereference bugs.

Category: Bug

Area: compiler:core

🔍 Analysis

• createSymbol() in binder.ts accepts node?: Node (optional/undefined), but the returned symbol's .node field is typed as Node (non-nullable).
• name-resolver.ts demonstrates a call passing undefined as node, confirming the type mismatch is exercised.
• Related helper functions that return Sym.node/Sym.declarations also propagate the incorrect non-nullable type.
• Fix would involve updating the Sym interface to type node as Node | undefined and declarations as (Node | undefined)[] (or filtering undefineds consistently), then fixing any resulting type errors at call sites.

📝 Suggested next steps

• Update Sym.node type to Node | undefined
• Update Sym.declarations type to reflect possible undefined entries, or ensure undefined is never pushed
• Fix downstream callers that now need to handle undefined

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