Derivations can now be printed in detail in `nix repl`
3842
Improvements
Lunaphied
Traditionally derivations printed in the REPL would only print a formatted object
representing the path of the derivation file it refers to. This makes inspecting
the enhanced derivation attribute sets encountered from mkDerivation or similar
wrappers more difficult. Even the :p/:print command would not elaborate attribute sets
tagged as a derivation.
With this change you can now use :p/:print to directly inspect a derivation
by providing one as the top-level object. Derivation attribute sets will only be
printed two levels deep and internal derivation attrsets will remain in unexpanded
path form as before. drvAttrs will also be elided as these attributes are already
present in the top-level attribute set of the derivation. These heuristics provide
a balance between readability and functionality. When the :p/:print is omitted,
a bare derivation is printed in the path format as before.
