With this, we don't have to copy the entire .drv closure to the
destination store ahead of time (or at all). Instead, buildPaths()
reads .drv files from the eval store and copies inputSrcs to the
destination store if it needs to build a derivation.

Issue #5025.

In particular, this now works:

  $ nix path-info --eval-store auto --store https://cache.nixos.org nixpkgs#hello

Previously this would fail as it would try to upload the hello .drv to
cache.nixos.org. Now the .drv is instantiated in the local store, and
then we check for the existence of the outputs in cache.nixos.org.

If a store doesn't support GC, then we don't need to warn about the
inability to create roots.

Also remove an erroneous comment.

Properly lock the builds of CA derivations

Make sure that we can’t build the same derivation twice at the same
time.

Fix https://github.com/NixOS/nix/issues/5029

nix repl: Update :edit doc to remove inaccurate use of "derivation"

It supports functions as well. Also change `package` to
`derivation` because it operates at the language level and does
not open the derivation (which would be useful but not nearly
as much).

It does not operate on a derivation and does not return a
derivation path. Instead it works at the language level,
where a distinct term "package" is more appropriate to
distinguish the parent object of `meta.position`; an
attribute which doesn't even make it into the derivation.

`:lf ref` does essentially the same thing as
`:a (builtins.getFlake "ref")` (but cannonicalising `ref` if needs be,
so that `:lf .` works)

Fix #3803

Use a dedicated make target for the man page rather than bundling the
generation as part of `install`.
Also make sure that `make install` is a fixpoint by

- Removing the generated markdown files from `MANUAL_SRCS`
- Not having the manpage generation write in its source directory so as
  to not update its timestamp (it would run each time otherwise)

Forward the whole Nix config to the repl subprocesses

Be more lenient when realisations have a conflicting dependency set

Some people want to avoid using registries at all on their system; Instead
of having to add --no-registries to every command, this commit allows to
set use-registries = false in the config. --no-registries is still allowed
everywhere it was allowed previously, but is now deprecated.

Co-authored-by: Eelco Dolstra <edolstra@gmail.com>

- This can legitimately happen (for example because of a non-determinism
  causing a build-time dependency to be kept or not as a runtime
  reference)
- Because of older Nix versions, it can happen that we encounter a
  realisation with an (erroneously) empty set of dependencies, in which
  case we don’t want to fail, but just warn the user and try to fix it.

Fill `NIX_CONFIG` with the value of the current Nix configuration before
calling the nix subprocesses in the repl
That way the whole configuration (including the possible
`experimental-features`, a possibly `--store` option or whatever) will
be made available.

This is required for example to make `nix repl` work with a custom
`--store`

Forward the whole Nix config to the post-build-hook

Fill `NIX_CONFIG` with the value of the current Nix configuration before
calling the post-build-hook.
That way the whole configuration (including the possible
`experimental-features`, a possibly `--store` option or whatever) will
be made available to the hook

nlohmann_json: Update to 3.9.1, fix use of internal copy

libexpr: Fix read out-of-bound on the heap

Signed-off-by: Pamplemousse <xav.maso@gmail.com>

Add a `devShells` attribute to the flake schema

Make `nix develop .#foo` search `.#devShells.${system}.foo` first