[Nix-dev] Re: `guile-1.6.7' fails to build

[Eelco Dolstra]

Hi,

Ludovic Courtès wrote:

>> You are right, nix isn't totally pure.
>> Eg a lot of package do contain optimizations for different processors.
>> These settings are set to [autodetect] by the configure script at many
>> packages.
> 
> Speaking of this, how does Nix ensure that `configure' scripts won't
> discover things (programs, libraries, C include files, etc.) outside the
> Nix store?

Nix itself doesn't do anything to prevent this (it can't --- not without tricks
like doing the build in a chroot, which would be nice to have but are less
portable).  However, in Nixpkgs there a bunch of tricks to prevent "impurities".
 For instance, GCC and ld are patched to not search in standard locations like
/usr/include, and the gcc-wrapper script barfs if you pass it a path outside of
the Nix store or the build's temporary directory.  And of course the environment
is cleared to prevent search paths like $PATH from affecting the builder.

But we can't stop a configure script from finding (say) /usr/bin/perl and
calling it.  This is in fact one of the reasons why we made NixOS --- there is
no /usr/bin/perl, so configure can't find it ;-)  (The build farm that produces
our releases runs on NixOS, so if channel packages have hidden dependencies on
files outside /nix/store, the build farm will reveal this.)

-- 
Eelco Dolstra | http://www.cs.uu.nl/~eelco