The current algorithm creates attributes with null values for packages
with no source in a variant of MELPA. Though will satify dependencies
they produce no files, and though a build that transitively depends on
one them will be successful, Emacs won't find them and any code
depending on them won't work.
The solution with minimal code change would have been filtering the
list of results from melpaDerivation by comparing the value against
null, but that leads to an infinite recursion.
This commit also moves legacy renames from the shared to the unstable
set, as the corresponding null value elements won't exist in the
stable set anymore.
The test used for the problem was:
$ nix-build --show-trace ./default.nix -A emacs26Packages.melpaStablePackages.findr
error: expression does not evaluate to a derivation (or a set or list of those)
The expected output, obtained with this commit is:
$ nix-build --show-trace ./default.nix -A emacs26Packages.melpaStablePackages.findr
error: attribute 'findr' in selection path 'emacs26Packages.melpaStablePackages.findr' not found
This approach has several differences with emacs2nix:
- the updater uses a downloaded recipes.json and archive.json for commit information, it uses a local checkout only for hashing the recipes
- the generated file is JSON
- the updater is written in emacs lisp
- prefetch errors are put into an error key in the JSON, for review + meta.broken attributes are generated from it
The updater re-uses the existing generated file to memoize prefetched content-sha256s for commits, thus prefetching should normally be quite fast.
