The default setting for extraLibs used to be the set of modules that come with
python by default but aren't usually enabled in our standard python derivation
because they require additional libraries. This meant that users who want to
*add* libraries to that set had to use a fairly complicated override, to add
more entries without loosing the ones set by default.
After this patch, the "standard libraries" such as "curses' are listed in
stdLibs while the extraLibs argument remains empty by default. This allows
users to override extraLibs without overriding the standard libraries.
Furthermore, the wrapper environment can be messed around with in an
additional 'postBuild' step. One nice application of this build step is
to patch scripts and binaries to use the wrapped python interpreter
instead of the pristine one, thereby enabling them to pick up all
modules that have been configured. The following example shows how this
is done for the 'pylint' utility:
pkgs.python27Full.override {
extraLibs = [pkgs.pylint];
postBuild = ''
cd ${pkgs.pylint}/bin
for i in *; do
rm $out/bin/$i
sed -r -e "s|^exec |exec $out/bin/python -- |" <$i >$out/bin/$i
chmod +x $out/bin/$i
done;
'';
};
The ghcWithPackage expression now has an argument 'ignoreCollisions' that
allows users to disable the path collision check like so:
(pkgs.haskellPackages.ghcWithPackages (pkgs: with pkgs; [ haskellPlatform ])).override { ignoreCollisions = true; };
See d64917ad17
for a long and detailed discussion of why these path collisions may occur.
Haskell packages -- i.e. packages built by our Cabal builder -- invariably have
the attributes 'pname' and 'version'. We use the absence of these attributes to
recognize non-Haskell packages and filter them from the closed package set
generated by closePropagation. We do this so that the generated Haskell
environment won't contain paths like "/lib/libz.a", which are part of the
closure but have nothing to do with Haskell.
The previous scheme used the attribute 'ghc' to accomplish the same thing, but
unfortunately other packages to contain a 'ghc' attribute, too, like the
old-style ghc-wrapper. Including the ghc-wrapper in this environment is
pointless, obviously. The new approach filters the ghc-wrapper successfully.
