This makes its behaviour consistent with the non-json
variant. Querying the outputs should be done by another command
(e.g. 'nix search')

This is useful for finding out what a registry lookup resolves to, e.g

  $ nix flake info patchelf
  Resolved URL:  github:NixOS/patchelf
  Locked URL:    github:NixOS/patchelf/cd7955af31698c571c30b7a0f78e59fd624d0229

Future editions of flakes or the Nix language can be supported by
renaming flake.nix (e.g. flake-v2.nix). This avoids a bootstrap
problem where we don't know which grammar to use to parse
flake*.nix. It also allows a project to support multiple flake
editions, in theory.

Usually this just writes to stdout, but for ProgressBar, we need to
clear the current line, write the line to stdout, and then redraw the
progress bar.

In the fully cached case for the 'nixpkgs' flake, it went from 101s to
4.6s. Populating the cache went from 132s to 17.4s (which could
probably be improved further by combining INSERTs).

This speeds up the creation of the cache for the nixpkgs flake from
21.2s to 10.2s. Oddly, it also speeds up querying the cache
(i.e. running 'nix flake show nixpkgs/nixos-20.03 --legacy') from 4.2s
to 3.4s.

(For comparison, running with --no-eval-cache takes 9.5s, so the
overhead of building the SQLite cache is only 0.7s.)

In particular, we store whether an attribute failed to evaluate (threw
an exception) or was an unsupported type. This is to ensure that a
repeated 'nix flake show' never has to evaluate anything, so it can
execute without fetching the flake.

With this, 'nix flake show nixpkgs/nixos-20.03 --legacy' executes in
0.6s (was 3.4s).

It uses the evaluation cache now rather than the ad hoc JSON cache.

In particular, doing 'nix build /path/to/dir' now works if
/path/to/dir is not a Git tree (it only has to contain a flake.nix
file).

Also, 'nix flake init' no longer requires a Git tree (but it will do a
'git add flake.nix' if it's a Git tree)

Fixes

  $ nix copy
  warning: Git tree '/home/eelco/Dev/nix-flake' is dirty
  nix: src/nix/installables.cc:348: std::tuple<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, nix::FlakeRef, nix::InstallableValue::DerivationInfo> nix::InstallableFlake::toDerivation(): Assertion `state->store->isValidPath(drvPath)' failed.
  Aborted (core dumped)

This means you now get an error message *before* stuff gets built:

  $ nix copy .#hydraJobs.vendoredCrates
  error: you must pass '--from' and/or '--to'
  Try 'nix --help' for more information.

Fixes

  $ nix copy .#hydraJobs.vendoredCrates --to /tmp/nix
  error: path '/nix/store/...' is not valid

Rename nix app and nix run commands

Since we've changed a lot of things in the 'nix' command (e.g. rename
'nix run') there is not much point in keeping this around.

Co-authored-by: Jörg Thalheim <Mic92@users.noreply.github.com>

InstallableValue has children InstallableFlake and InstallableAttrPath, but InstallableFlake was overriding toDerivations, and usage was changed so that InstallableFlake didn't need cmd. So these changes were made:
InstallableValue::toDerivations() -> InstalllableAttrPath::toDerivations()
InstallableValue::cmd -> InstallableAttrPath::cmd

InstallableValue uses state instead of cmd

toBuildables() and toDerivations() were made abstract

This reverts commit 883948d.

This completes flakerefs using the registry (e.g. 'nix<TAB>' => 'nix
nixpkgs') and flake output attributes by evaluating the flake
(e.g. 'dwarffs#nix<TAB>' => 'dwarffs#nixosModules').

macOS doesn't have GLOB_ONLYDIR.

Installables refactor

Generic shell completion support for the 'nix' command

Co-authored-by: Jörg Thalheim <Mic92@users.noreply.github.com>

This makes 'nix flake' less cluttered and more consistent (it's only
subcommands that operator on a flake). Also, the registry is not
inherently flake-related (e.g. fetchTree could also use it to remap
inputs).

 into flakes

…lakes

The attributes previously stored in TreeInfo (narHash, revCount,
lastModified) are now stored in Input. This makes it less arbitrary
what attributes are stored where.

As a result, the lock file format has changed. An entry like

    "info": {
      "lastModified": 1585405475,
      "narHash": "sha256-bESW0n4KgPmZ0luxvwJ+UyATrC6iIltVCsGdLiphVeE="
    },
    "locked": {
      "owner": "NixOS",
      "repo": "nixpkgs",
      "rev": "b88ff468e9850410070d4e0ccd68c7011f15b2be",
      "type": "github"
    },

is now stored as

    "locked": {
      "owner": "NixOS",
      "repo": "nixpkgs",
      "rev": "b88ff468e9850410070d4e0ccd68c7011f15b2be",
      "type": "github",
      "lastModified": 1585405475,
      "narHash": "sha256-bESW0n4KgPmZ0luxvwJ+UyATrC6iIltVCsGdLiphVeE="
    },

The 'Input' class is now a dumb set of attributes. All the fetcher
implementations subclass InputScheme, not Input. This simplifies the
API.

Also, fix substitution of flake inputs. This was broken since lazy
flake fetching started using fetchTree internally.

Closes NixOS#3520.

Caches tree in addition to lockedRef, and explicitly writes out the logic for different combinations of cached/uncached flakes and indirect/resolved/locked flakes. This eliminates uneccessary calls to lookupInFlakeCache, fetchTree, maybeLookupFlake, and flakeCache.push_back

…ovements

Cache tree in fetchOrSubstituteTree