fix: support array form of tsconfig "extends" in document links

[Andrei L (unrevised6419)]

Description

TsconfigLinkProvider (in extensions/typescript-language-features/src/languageFeatures/tsconfig.ts) only created a document link when the extends field was a string. TypeScript 5.0 added support for an array of base configs:

{
  "extends": ["./tsconfig.base.json", "@tsconfig/strictest/tsconfig.json"]
}

In that case, the existing code asked jsonc.findNodeAtLocation(root, ['extends']) and handed the resulting node straight to tryCreateTsConfigLink. isPathValue requires node.type === 'string', so the array case was silently dropped — Cmd+Click did nothing on any of the entries.

This change renames getExtendsLink to getExtendsLinks and:

• returns [] when no extends is present
• iterates array children via the existing mapChildren helper when extends is an array
• falls through to the original single-string behavior otherwise

Each element is resolved through the unchanged tryCreateTsConfigLink → openExtendsLinkCommandId → getTsconfigPath pipeline, so relative paths, absolute paths, and node_modules package resolution continue to work per element.

For consistency, all three sibling getters (getExtendsLinks, getFilesLinks, getReferencesLinks) now carry an explicit (vscode.DocumentLink | undefined)[] return type. The outer coalesce in provideDocumentLinks is unchanged and still filters the undefined entries.

Reference: TypeScript 5.0 release notes – Supporting Multiple Configuration Files in extends.

How to test

1. Open a workspace containing a tsconfig.json such as:

   {
     "extends": ["./tsconfig.base.json", "./tsconfig.strict.json"]
   }

   with both referenced files present next to it.
2. Hover each string inside the extends array — a "Follow link" tooltip should appear.
3. Cmd+Click (Ctrl+Click on Windows/Linux) each entry and confirm the correct file opens.
4. Confirm the existing single-string form still works:

   { "extends": "./tsconfig.base.json" }

5. Confirm files and references links are unaffected.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates the tsconfig document link provider to support multiple extends entries by handling extends as either a single value or an array.

Changes:

• Replace single extends link generation with multi-link generation.
• Add support for extends: [] by iterating array children and creating links per entry.

[Andrei L (unrevised6419)]

@microsoft-github-policy-service agree

[Andrei L (unrevised6419)]

Closing in favor of #334894, which covers this along with every other tsconfig value that names a file or a directory, behind a table-driven provider.

For this change specifically: the array form of extends now falls out of the contribution table as a second row rather than needing its own branch, so the string and array forms share one code path.