microsoft / microsoft/TypeScript

Lib dependencies are transitive

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Description

TypeScript Version: 3.8.3

Search Terms: lib target dependencies triple-slash

Code

I have a reproduction repository at https://github.com/astorije/repro-tsc-lib-issue.
Essentially, consider the following code:

console.log(Object.values({ foo: BigInt(42) }));

Object.values is a ES2017 feature, and BigInt is a ES2020.
Also consider the target is tsconfig.json is es2015, and lib is either not specified or simply contains es2015 and dom.

Expected behavior:

Given the code and the TS configuration above, the type checker should always fails with:

index.ts:2:20 - error TS2339: Property 'values' does not exist on type 'ObjectConstructor'.

2 console.log(Object.values({ foo: BigInt(42) }));
                     ~~~~~~

index.ts:2:34 - error TS2304: Cannot find name 'BigInt'.

2 console.log(Object.values({ foo: BigInt(42) }));
                                   ~~~~~~

And if you only have typescript as a dependency in package.json, that is indeed what you'll get. So far, so good. See the expected folder of my repro repo.

Actual behavior:

If you have a (direct or indirect) dependency to @types/node, or if any dependency contains a declaration file that has /// <reference lib="es2018" />, /// <reference lib="es2020.bigint" />, etc., the type checker will now stop reporting these errors. See the actual folder of my repro repo.

This seems significant to me because it means that dependencies can silence potential browser incompatibilities. If I specified a target of es2015, with no extra lib, Babel transpiling, or polyfills, I should not be able to compile the code above.

Is there something obvious I'm missing? I realize it's the very design of libbut as explained in #15732, that assumes the project uses polyfills, which is not something that can be enforced/checked by a third-party library at compile time.

Related Issues:

Apologies for the vagueness of the search terms. It's significant enough that it must already exist in an issue or a StackOverflow question, but after spending some time looking, I did not find anything similar.

The only issues that seem somewhat related, but different:

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the reproduction repository and compare its expected and actual folders using TypeScript 3.8.3. Read the tsconfig.json and index.ts examples, then review related issues #33111, #35656, and #15732. Done means determining whether transitive declaration references should silence the reported Object.values and BigInt errors, and documenting or correcting that behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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