The pip locker [sometimes created a URL without hash][1] to reflect that there was a local source.
This produced the following error when trying to evaluate that derivation:
… from call site
at /nix/store/qdzdi6qvrqxfqxhi3j70d5dsl9f5jpby-source/modules/dream2nix/pip/default.nix:86:28:
85| mkDerivation = {
86| src = l.mkDefault (fetchers.${metadata.sources.${config.name}.type} metadata.sources.${config.name});
| ^
87| doCheck = l.mkDefault false;
… while calling 'url'
at /nix/store/qdzdi6qvrqxfqxhi3j70d5dsl9f5jpby-source/modules/dream2nix/pip/default.nix:57:11:
56| fetchers = {
57| url = info: l.fetchurl {inherit (info) url sha256;};
| ^
58| git = info: config.deps.fetchgit {inherit (info) url sha256 rev;};
error: value is null while a string was expected
Of course, one cannot call `builtins.fetchurl` without a `sha256` argument.
Now, local dependencies are specified exactly like that in the lock file. Now, we'll fetch nothing when dealing with local dependencies.
Also, their evaluation when generating `preFixup` attribute is delayed until build time. This was a bigger problem due to the previous bug, but in any case it should still help to reduce evaluation overhead.
FWIW, sometimes local sources might not really exit in the derivation source tree until build time. For example, when building aggregated sources with meta-repo management tools such as Mr. Chef.
[1]: 40b65e4598/pkgs/fetchPipMetadata/src/fetch_pip_metadata/lock_file_from_report.py (L72C28-L72C28)
