Composite projects: support strict dependencies #36743
Description
Google (and Bazel rules_typescript) use a special-purpose TypeScript compiler. One of the reasons for this is we want to enforce strict dependencies.
Strict dependencies means you may only import or reference symbols declared in a project you explicitly declare to be an input. This is an essential property in a large monorepo as a defense against accidental coupling between projects.
For example we might have three directories, A B and C:
alexeagle@alexeagle:~/Projects/repro_strict_deps$ cat A/a.ts
export const a = 'hello';
alexeagle@alexeagle:~/Projects/repro_strict_deps$ cat A/tsconfig.json
{
"compilerOptions": {
"composite": true
}
}
alexeagle@alexeagle:~/Projects/repro_strict_deps$ cat B/b.ts
import {a} from '../A/a';
export function sayHello(f: string) {
console.log(a + f);
}
alexeagle@alexeagle:~/Projects/repro_strict_deps$ cat B/tsconfig.json
{
"compilerOptions": {
"composite": true,
},
"references": [
{"path": "../A"}
]
}
alexeagle@alexeagle:~/Projects/repro_strict_deps$ cat C/c.ts
import {a} from '../A/a'; // SHOULD FAIL HERE
import {sayHello} from '../B/b';
sayHello('world');
console.error(a);
alexeagle@alexeagle:~/Projects/repro_strict_deps$ cat C/tsconfig.json
{
"references": [
// NO REF TO A
{"path": "../B"}
]
}
Let's say we work on library B. We decide we no longer need to depend on A, so we remove the dependency, but this breaks users such as C. This is a serious impediment to good code practices because our dependency on A leaked to users who reference its symbols without declaring their own dependency. In a big monorepo, the breakage of removing a dependency can prevent ever cleaning them up
We would like to propose a strictness setting when used with Project References, such that imports (or ambient references) from transitive dependencies should be disallowed.
/cc @evmar @josephperrott