Find references even when TypeScript sub-projects not yet open

[dcecile]

From microsoft/vscode#65102...

It seems like with a multiple-tsconfig.json setup, VS Code can't find all references. (Even though technically all of them should be "joined" via a root tsconfig.json that uses project references.)

Here's a minimal repro of my setup: https://github.com/dcecile/typescript-references-test

common/
  message.ts
  tsconfig.json
server/
  hello.ts
  tsconfig.json
client/
  sharedMain.ts
  tsconfig.json

• Both client and server reference the common project
• "Find references" fails to find the references to the common function
• "Rename symbol" also fails to rename the references
• After loading files from the client and server projects, find references works

[mjbvz]

Confirmed with TypeScript 3.5.0-dev.20190407

[sheetalkamat]

This is currently known issue in which if the file is not open or declaration maps are not present it cannot find all references in sibling projects. #28261 is wip for this but needs more work before can be merged in since we need to be smart about when to lookup symbol in other projects(as loading projects in most common scenarios is costly and can result in delay when someone does first time find all references)

[awerlang]

@RyanCavanaugh I believe the Duplicate label is a mistake here.