Re: [PATCH 0/2] native-search-paths for GHC

[ludo@gnu.org (Ludovic Courtès)]

Eric Bavier <ericbavier@openmailbox.org> skribis:

> On 2015-10-07 11:07, Federico Beffa wrote:

[...]

>> * If I understand correctly, the configuration files of dependencies
>> are
>>   copied in a unique directory for each package.  Instead of copying
>>   would a symlink work? (There are literally thousands of packages on
>>   Hackage and hopefully Guix will get more of them.)
>
> I don't know if symlinking is allowed across store directories, though
> if it is, that'd be something to try.

Yes it’s allowed.  That’s what ‘union-build’ (the procedure that builds
profiles) does.

>> * Some Haskell libraries have a rather large list of dependencies. For
>>   this reason I can imagine that in some situations GHC_PACKAGE_PATH
>>   could grow rather long.
>
> Not every package would end up with an entry in GHC_PACKAGE_PATH, only
> those that are installed, or declared inputs.  Dependent libraries
> would be found when GHC examines the package databases of those
> packages.
>
>>   This thought made me wonder if there is a
>>   maximum length to the value of environment variables that we could
>>   possibly hit.
>
> We've already pushed this quite far.  E.g. the hydra package creates a
> rather sizable PER5LIB path.

Nice.  :-)

AFAIK there’s no limit on the size of an environment variable’s value.

However, it’s a good idea to keep search paths small, to reduce the
number of ‘stat’ calls that have to be done before a given file is
found.

Using a symlink forest is a good way to achieve that.

Thanks,
Ludo’.