Re: [Caml-list] Suggested way to determine platform specific capabilities in build system?

["Daniel Bünzli" <daniel.buenzli@erratique.ch>]

Le dimanche, 19 avril 2015 à 08:47, Adrien Nader a écrit :
> This is the wrong approach. Please do not test for systems but for
> capabilities. Testing for systems hinders progress and is a huge
> long-term cost.

It depends quite a lot of what you need to do, e.g. in the ocamlbuild example I linked to, you need to add a specific flag to the compiler, now if you need to check for this using some kind of obscure test your are building quite a few assumptions about how the tool works and the semantics of the flag both of which may change in the future regardless of the you may think about them. These kind of things lead to quite obscure configuration systems which also do have a huge cost both for *users* and maintainers in the long-term.

> The proper way to do it is to test for features instead. Want to know if
> function foo is available in library bar? Well, just reference it and
> see if compilation and/or linking fails.  

I know this is the way autocrap likes to work; it may seem smart but I think that's completely retarded. We want versioned APIs/system releases that are clear about the symbols they expose and their associated semantics. I mean if we take to the extreme why have any form of package constraints in opam ? We could just test needed symbols/modules against what is installed. I hope you do realize that this is completely insane.   

Nowadays that it has never been as easy to use a patched package (under the form of `opam pin`) and that I hope we will also soon fix the problem of making reliable releases in a breeze. I think that the kind of approach you propose is going to be more much more expensive in the long term. The simpler you keep the configuration bits the easier it will be to adapt both from you as a maintainer or from someone that is external to the project.  

The approach you mention would make sense if the OSes would provide us a reliable service for testing its capabilities. Lacking this, relying on obscure and brittle test shell scripts, thanks but no. Progress is not hindered by what you make think...

Best,

Daniel