@types/mysql should be in devDepenencies

@types inclusion should be optional. Use case: in our project we share code for client and server, and server types conflict with client types. Consider setInterval, which has different return type on Node and DOM.

Also, I think that this is the convention for many libraries, since TypeScript in general is optional.

[move-zig]

There was a bit of a discussion about this on https://gitter.im/DefinitelyTyped/DefinitelyTyped from Nov 06 19:47 to Nov 07 08:23 (ET, I think). It seems like the consensus was a standard dependency, not devDependency. I think that makes sense.

[gamliela]

I understand the rationale for this change. Still, there is a reason why many libraries put it in devDependencies after all, and some of these reasons are given in the links you presented.

Here are my arguments:

1. TypeScript is not mandatory. By putting types in the dependencies section you signal that the types are essential and required part of the project, which is not the case.

2. It is easy to add @types for those who want it, but it is much harder to remove it for those who don’t want it (like me). For me, it involves to write a specific postinstall script to deal with this problem.

3. There is a technical problem that affect (probably minority) of users. Some types are inferred incorrectly. See discussion at the end of this thread, and note that eventually they chose to put @types/node at devDependencies.

I will try to explain # 3 from our perspective. A variation of our problem is demonstrated also here.

We have sever code (Node) and client code (ES5) on the same project tree. Both share the same tsconfig file and both code parts get compiled together. Let’s put aside the question whether it’s a good setup or not; that’s the way we work now and I assume we are not the only ones that work this way. In our client code we have expressions like setTimeout(...). We actually mean window.setTimeout(...) (doc) and therefore expect to get a number type as result. But because of the inclusion of @types/node (as side effect of @types/mysql inclusion) the TypeScript compiler automatically picks the node version of setTimeout, which returns a Timer object instead of number. So we ends up with TS2323: Type 'Timer' is not assignable to type 'number' error.