Repository: TypeScript
Issue: TypeScript 3.9: Type files are behaving like included files
Labels: Needs Investigation

I'm trying to use the new TypeScript code editor support for solution projects and it's working pretty well, but has the issue mentioned in the title.

When I add typeRoots or a type file, the referenced file isn't used just to get types from it. Instead, it acts like an included file for that project and the file's type checking follows that project configuration in the editor.

tsconfig.json

```json
{
  "files": [],
  "references": [
    {
      "path": "./tsconfig.client.json"
    },
    {
      "path": "./tsconfig.server.json"
    },
    {
      "path": "./tsconfig.shared.json"
    }
  ]
}
```

tsconfig.base.json

```json
{
  "compilerOptions": {
    "baseUrl": "./",
    "composite": true,
    "declarationDir": "./@types",
    "emitDeclarationOnly": true,
    "lib": [
      "ES5"
    ],
    "target": "ES5",
    "typeRoots": [
      "node_modules/@types/",
      "lib/types/"
    ]
  }
}
```

tsconfig.client.json

```json
{
  "extends": "./tsconfig.base.json",
  "compilerOptions": {
    "lib": [
      "ES6",
      "DOM"
    ],
    "target": "ES6",
    "types": [
      "client",
      "shared" // This line is the problem
    ]
  },
  "exclude": [
    "lib/types/shared/"
  ],
  "include": [
    "lib/types/client/"
  ]
}
```

tsconfig.shared.json

```json
{
  "extends": "./tsconfig.base.json",
  "compilerOptions": {
    "types": [
      "shared"
    ]
  },
  "include": [
    "lib/types/shared/"
  ]
}
```

lib/types/shared/index.d.ts

```typescript
type ShouldNotHaveDomLib = Element; // This works, but should output an error
```

It seems like an issue with VSCode as building the project with "tsc --build" does throw the expected error:

> lib/types/shared/index.d.ts:1:28 - error TS2304: Cannot find name 'Element'.
>
>1 type ShouldNotHaveDomLib = Element;

I found that removing the "shared" types from tsconfig.client.json made the client types unavaliable as expected, but then made the server ones avaliable, as the "server" project is the second on the reference list.

With this, I found a very simple solution: put "shared" project as the first referenced in "tsconfig.json"

```json
{
  "files": [],
  "references": [
    {
      "path": "./tsconfig.shared.json"
    },
    {
      "path": "./tsconfig.client.json"
    },
    {
      "path": "./tsconfig.server.json"
    }
  ]
}
```

This solves the issue for me and yes, building the shared project first should be the standard, so not a huge deal for people using this project pattern. Still, it still is an unexpected behaviour and there might be some other patterns where this is a bigger issue.

I searched for issues here, on TypeScript and Javascript and Typescript Nightly and found nothing, so I apologize if this is a duplicate and/or should be reported to one of those repositories.

- VSCode Version: 1.44.2 (testes in latest insider too)
- OS Version: Windows 10 19608

Steps to Reproduce:

1. Download the Javascript and Typescript Nightly extension
2. Set up project as above
3. Add some types to types/client/index.d.ts
4. Try to use those types in types/server/index.d.ts

Does this issue occur when all extensions are disabled?: No, because I do need the Javascript and Typescript Nightly extension to use TS 3.9 features. However, it still happens while using it with only this extension.