This properly implements revert in
0729f60697.
We used to have which='type -P' alias, but really it's best to just
rely on which package, only 88K in size.
cc @edolstra
- Now `pkg.outputUnspecified = true` but this attribute is missing in
every output, so we can recognize whether the user chose or not.
If (s)he didn't choose, we put `pkg.bin or pkg.out or pkg` into
`systemPackages`.
- `outputsToLink` is replaced by `extraOutputsToLink`.
We add extra outputs *regardless* of whether the user chose anything.
It's mainly meant for outputs with docs and debug symbols.
- Note that as a result, some libraries will disappear from system path.
The most complex problems were from dealing with switches reverted in
the meantime (gcc5, gmp6, ncurses6).
It's likely that darwin is (still) broken nontrivially.
The previous default was $out/lib/debug, which wasn't very useful.
This ensures that you can do
environment.systemPackages = [ pkgs.hello.debug ];
to install debug info.
`man 1 info` says:
The first non-option argument, if present, is the menu entry to
start from; it is searched for in all `dir' files along INFOPATH.
If it is not present, info merges all `dir' files and shows the
result. Any remaining arguments are treated as the names of menu
items relative to the initial node visited.
Which means that this does what previous programs/info did and #8519
(on-the-fly infodir generation for Emacs) wanted to do, but for both
programs.
This improves error messages when a set or a list is used where a path
was expected. For an example, if you used a package set (as opposed to a
single package) in systemPackages before this commit, the error was:
```
cannot coerce a list to a string, at "/home/nixpkgs/lib/types.nix":103:37
```
Now, the error message reads:
```
The option value `environment.systemPackages' in `/etc/nixos/configuration.nix' is not a list of paths.
```
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
