Implement methods for shim scripts

[vitorgalvao]

@caskroom/maintainers This replaces #9203. Everyone agrees shim scripts are desirable, so lets allow them.

On a first phase, if anyone submits a cask that employs a shim script (usually inside a preflight and using ruby methods to write to a file), we should (after determining it is indeed necessary and we have no other way to fix the problem) accept it and add a comment mentioning it’s a shim (this will allow us to find them easier to study/replace).

On a second phase (the point of this issue), we should implement something to make those easier to make. So, two points:

• Should we really implement something to make them easier, or should we just accept them in their usual rough form (has the advantage of not encouraging them, which is good since they should be used as a last resort)?
• Any suggestions for implementations/interface?

[adidalal]

https://github.com/caskroom/homebrew-cask/blob/master/Casks/minecraft-server.rb - add comment, based on instructions from http://minecraft.gamepedia.com/Tutorials/Setting_up_a_server#OS_X_instructions
#9101 - needs new PR w/ comment

[vitorgalvao]

#15876 doesn’t apply, because the shim isn’t necessary (the tool officially creates the necessary script).

[psibre]

@vitorgalvao thanks for the heads up and for quickly merging #18827 -- I'll see if I can contribute a test and shim script

[psibre]

A thought occurs: is it even possible to add some sort of test to ensure that the shim script works correctly? I'm thinking of something along the lines of the test block in homebrew formulas...

[vitorgalvao]

@psibre No, we don’t have anything like that. Shim scripts should be discouraged, though (and only used in specific situations). This is not really related to this issue at hand (this issue is about deciding on an interface for shim scripts), so I ask that you open a new issue for further questions (every caskroom mantainer is likely getting an email to each reply to this issue, so we should really stay on topic).

[adidalal]

What's the official comment for a shim script?

[vitorgalvao]

What's the official comment for a shim script?

I guess # shim script (https://github.com/caskroom/homebrew-cask/issues/18809) is OK.