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nixpkgs/pkgs/development/dhall-modules/lib.nix
Gabriel Gonzalez 87d5e6fc1a Change idiom for overriding Dhall package version
Before this change, a Dhall package like the Prelude would be
encoded as a record with one field per supported version.  Then
downstream packages would specify which package to override
by selecting a different record field.

The problem with that approach is that it did not provide an
easy way to override a package to a version other than the default
ones supplied by Nixpkgs.  Normally you would use the `.override`
method for this purpose, but the `override` method added by
`buildDhall{Directory,GitHub}Package` is clobbered by the
`override` method added by `callPackage` in
`./pkgs/top-level/dhall-packages.nix`.

The solution is to add a separate `.overridePackage` method which is
essentially the exact same as `.override`, except that it is no
longer clobbered by `callPackage`.  This `.overridePackage` method
allows one to override the arguments supplied to
`buildDhall{Directory,GitHub}Package`, making it easier to specify
package versions outside of the ones supported by Nixpkgs..

This also includes a change to only build one (preferred) version of each
package (instead of multiple supported versions per package), in order to
minimize the maintenance burden for the Dhall package set.
2020-11-11 11:16:04 +01:00

26 lines
696 B
Nix

{ lib }:
let
# This is essentially the same thing as `lib.makeOverridable`, except storing
# the override method in a method named `overridePackage` so that it's not
# shadowed by the `override` method added by `callPackage`
makePackageOverridable = f: args:
let
result = lib.makeOverridable f args;
copyArgs = g: lib.setFunctionArgs g (lib.functionArgs f);
overrideWith =
update: args // (if lib.isFunction update then update args else update);
overridePackage =
copyArgs (update: makePackageOverridable f (overrideWith update));
in
result // { inherit overridePackage; };
in
lib // {
inherit makePackageOverridable;
}