that there are some places in Nixpkgs (php_configurable /
composableDerivation, it seems) that call `derivation' with
incorrect arguments (namely, the `name' attribute missing) but get
away with it because of laziness.
* Removed exprToString and stringToExpr because there is no ATerm
representation to work on anymore (and exposing the internals of the
evaluator like this is not a good idea anyway).
allowed. So `name1@name2', `{attrs1}@{attrs2}' and so on are now no
longer legal. This is no big loss because they were not useful
anyway.
This also changes the output of builtins.toXML for @-patterns
slightly.
intersectAttrs returns the (right-biased) intersection between two
attribute sets, e.g. every attribute from the second set that also
exists in the first. functionArgs returns the set of attributes
expected by a function.
The main goal of these is to allow the elimination of most of
all-packages.nix. Most package instantiations in all-packages.nix
have this form:
foo = import ./foo.nix {
inherit a b c;
};
With intersectAttrs and functionArgs, this can be written as:
foo = callPackage (import ./foo.nix) { };
where
callPackage = f: args:
f ((builtins.intersectAttrs (builtins.functionArgs f) pkgs) // args);
I.e., foo.nix is called with all attributes from "pkgs" that it
actually needs (e.g., pkgs.a, pkgs.b and pkgs.c). (callPackage can
do any other generic package-level stuff we might want, such as
applying makeOverridable.) Of course, the automatically supplied
arguments can be overriden if needed, e.g.
foo = callPackage (import ./foo.nix) {
c = c_version_2;
};
but for the vast majority of packages, this won't be needed.
The advantages are to reduce the amount of typing needed to add a
dependency (from three sites to two), and to reduce the number of
trivial commits to all-packages.nix. For the former, there have
been two previous attempts:
- Use "args: with args;" in the package's function definition.
This however obscures the actual expected arguments of a
function, which is very bad.
- Use "{ arg1, arg2, ... }:" in the package's function definition
(i.e. use the ellipis "..." to allow arbitrary additional
arguments), and then call the function with all of "pkgs" as an
argument. But this inhibits error detection if you call it with
an misspelled (or obsolete) argument.
NixOS evaluation errors in particular look intimidating and
generally aren't very useful. Ideally the builtins.throw messages
should be self-contained.
