check .d.ts files

[achingbrain]

We don't appear to run any sort of checking on .d.ts files, this means the syntax across modules is inconsistent and worse, we can ship with syntax errors and other obvious-in-hindsight bugs.

Some suggestions:

1. Enable linting for .d.ts files
2. Test .d.ts files to catch things like:

import type { Derpstore } from 'interface-datastore'

(1) is quite straight forward but for (2) maybe we could include a tsd test command?

[achingbrain]

cc @hugomrdias @Gozala

[Gozala]

I have no strong feelings about it, that said it’s not just our linter, typescript itself (or at least vscode) seems to not report lot of issues either. I often change file extension to .ts and then back.

Aegir also has to do some special handling of .d.ts files.

All this custom setup and divergence from default toolchains makes things harder for everyone. I wonder what were the reasons to switching from .ts files to .d.ts (which worked as expected with native toolchains) and whether those reasons still make sense and do a outweigh tradeoffs.

[achingbrain]

This is basically a nightmare. The only way to check your .d.ts files is to turn off skipLibCheck, then you end up checking everything in node_modules too, no way to exclude them. Ref: microsoft/TypeScript#30511

I wonder what were the reasons to switching from .ts files to .d.ts

Not sure we ever switched - we wanted .d.ts generated from jsdoc only initially since it doesn't require people to know ts to contribute.

We then backtracked a little and added .d.ts when it became apparent that jsdoc has a bunch of downsides like duplication of types and it being hard to define certain structures.

The tooling for .d.ts seems quite lacking, I think because they're not really supposed to be hand written so maybe defining types in .ts is the way forward in order to ensure higher quality until the situation improves.

[Gozala]

Not sure we ever switched - we wanted .d.ts generated from jsdoc only initially since it doesn't require people to know ts to contribute.

We definitely have switched because typedefs I've originally put in ipfs-core-types had .ts extensions, but somewhere down the line they've turned .d.ts.

[Gozala]

Checked history and it seems like this is a change that did it ipfs/js-ipfs@a418a52#diff-ecc32b520be57da677d45d1b0c7d5f883328286d8de03159de95e1eb680d08df

[achingbrain]

Closing as the resolution is to declare types in .ts files in order to get a more compile-time safety from the compiler.