Configured optional dependencies are not optional

[thasmo]

Installing gulp-imagemin using yarn fails - for some reason - to install the optional dependencies, which results in this error when running gulp:

Error: Cannot find module 'imagemin-jpegtran'

This happens probably because the optional dependencies are required nonetheless.

npm's documentation states the following regarding optional dependencies:

It is still your program's responsibility to handle the lack of the dependency. ...

[thasmo]

Just found a related issue.

[sindresorhus]

Sure. PR welcome. Weird that it works with npm though.

I've commented here how it should be implemented: #224 (comment)

[ekryski]

I'm actually having this with NPM as well.

[ekryski]

@sindresorhus how do you want to handle it? Just make them regular dependencies?

[michelecocuccio]

Having the same problem here using NPM :(

[DevanB]

Same issue here. Seems to be gifsicle being the problem for me.

Using NPM.

[rejas]

I am really baffled about this thread. Especially that @sindresorhus writes "Weird that it works with npm though." when this PR exists for month: #185
Now I am wondering what I should have done differently to get this through or heard like this thread....