Should project references check for transitive references to do the declaration file include check

[sheetalkamat]

Issue created from #27195 (review)
Need to identify what needs to happen in this scenario:

Does this work for transitive projectReferenes? I'm asking because I struggled with that too.

// @filename: tsconfig.a.json
{"compilerOptions": {"composite"}, "files": ["a.ts"]}

// @filename: a.ts
export class A {}

// @filename: tsconfig.b.json
{"compilerOptions": {"composite"}, "files": ["b.ts"], "references": [{"path": "tsconfig.a.json"}]}

// @filename: b.ts
import {A} from './a';
export const b = new A();

// @filename: tsconfig.c.json
{"files": ["c.ts"], "references": [{"path": "tsconfig.b.json"}]}

// @filename: c.ts
import {b} from './b';
console.log(b);

Compiling tsconfig.c.json should resolve imports as b.d.ts and a.d.ts. I guess the current implementation resolves imports to b.d.ts and a.ts.

[ajafff]

I verified that this is a problem in the newest nightly release. After all these recent refactorings, it resovles to the original files of transitive project references, even if outDir option is used. Previously this was only an issue if ourDir === rootDir.

[ajafff]

@RyanCavanaugh @sheetalkamat I assume the changes that lead to this issue landed/will land in ts@3.1. Will there be a fix for this issue in ts@3.1? The current behavior regarding transitive project references defeats the whole purpose of the feature. This is especially a problem in big projects with a deep hierarchy of project references.

• compiler needs to parse and check the source of transitive project references
• different compilerOptions in referenced projects may cause unexpected compiler errors
• --watch will rebuild for changes that don't affect emitted declaration files

[sheetalkamat]

I will let @RyanCavanaugh triage this for 3.1 but the work here is more involved as you pointed out. We are yet to chat what are the scenarios that are valid/not valid especially to tackle module resolution correctly. Once we have finalised on that we should be able to handle this correctly.