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nixpkgs/pkgs/development/interpreters/dhall/build-dhall-directory-package.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

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Nix

{ buildDhallPackage, lib }:
# This is a minor variation on `buildDhallPackage` that splits the `code`
# argument into `src` and `file` in such a way that you can easily override
# the `file`
#
# This function is used by `dhall-to-nixpkgs` when given a directory
lib.makePackageOverridable
( { # Arguments passed through to `buildDhallPackage`
name
, dependencies ? []
, source ? false
, src
, # The file to import, relative to the root directory
file ? "package.dhall"
}:
buildDhallPackage {
inherit name dependencies source;
code = "${src}/${file}";
}
)