Add support for @types declaration packages

[ChrisPearce]

Typescript v2 is moving to support a new approach to adding typings to a project.

Type definitions will be included in packages contained within the @types scope (e.g. @types/mypackage), which can simply be installed via npm (just like other packages).

More information can be found at:
https://blogs.msdn.microsoft.com/typescript/2016/06/15/the-future-of-declaration-files/

Currently any of these @types packages that are referenced in package.json, are incorrectly recognised as unused dependencies.

[lijunle]

Good feature!

Do you want to ignore all the @types packages? Or only the ones on use?

[ChrisPearce]

Ideally, it would be great to recognise the ones that are used, but if that doesn't prove possible it would be great to have an option that just ignores all @types scoped packaged.

[ChrisPearce]

As a workaround, I'm currently using the following command to ignore all @types scoped packages:
depcheck --ignores @types/*

[GongT]

In a typescript project, @types packages can be "used" with 3 different ways:

2 way in source code, that's simple to parse:

///<reference types="node"/>
import React from 'react';
import someThing from '@scoped/package'; // <- "@types/scoped__package"

another in tsconfig.json, but is complicated.
tsconfig.json document
( see section @types, typeRoots and types)

for each tsconfig found in project:

1. can be renamed to everything. it's just a JSON, no field is required. (And also can add extra fields you want)
2. can extend another one. every file on the chain can use as the final one.
3. once a tsconfig file result contains typeRoots, but "*bla/bla/*node_modules/@types" not included, then this file is nothing to do with @types.
4. if there is no typeRoots nor types, all @types package can mark as used. no other detection is needed in entire project.
5. if there is types field, only listed package used by this file.

("typeRoots" and "types" is sub field of "compilerOptions")

[GongT]

BTW, @types package should not appear in dependencies, but should always in devDependencies.
except some extreme rear situation.

[GongT]

Oh, When I start to write some code, I found that, the first 2 ways is also affected by tsconfig.json.
It's really hard to do a "complete" check....
I think this big job worth to create a new tool...

[mnkhouri]

@GongT thanks for the research, that does make it seem quite complex to properly detect @types usages when it is modified by tsconfig.json.

Instead of trying to analyze it ourselves, I wonder if there might be some way to extract this information from the typescript compiler? I haven't done a lot of research, but some documentation is here.

[GongT]

I have not look into depcheck's parser, current parseTypescript not load user's tsconfig.json, this need first update.

ts.transpile cannot used to analyze a "program", types option is hard code to undefined.

here is a simple script to list all files used when compile a project:
https://gist.github.com/GongT/1d5113a2ffd8ac7cac53123af61039d1

[conartist6]

I've opened a PR that would fix this. If people here could chip in a review perhaps it would speed the process of getting it shipped.

[ljharb]

This still doesn't seem solved - i'm still getting unused warnings for DT packages.

[SiRocke]

I've also made it to this point. Doing some major cleanup and it looks to still be an issue.

[navignaw]

I'm seeing an issue as well. My best guess is that the solution works for importing types directly, but does not work for the /// <reference types="foo" /> syntax.

Here's a reproducible example:

/// <reference types="w3c-web-usb" />

const supportsUsb = !!navigator?.usb

with this, depcheck reports

Unused devDependencies
* @types/w3c-web-usb

however, this works successfully with no error:

import type { default as foo } from 'w3c-web-usb'

const supportsUsb = !!navigator?.usb

[ljharb]

The point of DT types is that you import them from the non-DT package name.