Commit graph

639 commits

Author SHA1 Message Date
Eelco Dolstra
d9e8ab0ff2
Add a check for broken Boost versions
In some Boost versions, coroutines don't propagate exceptions
properly, causing Nix to fail with the exception 'coroutine has
finished'.
2018-07-31 16:35:05 +02:00
Eelco Dolstra
a92ed973e5
Store floating point numbers in double precision
Even on 32-bit systems, Value has enough space to hold a double.
2018-07-03 18:39:32 +02:00
Will Dietz
f601bc0492 sync.hh: return cv_status instead of dropping it, in case useful. 2018-06-18 17:31:00 -05:00
Eelco Dolstra
7d21863bb3
Make <nix/fetchurl.nix> run in constant memory
E.g.

  nix-build --store ~/my-nix/ -E 'import <nix/fetchurl.nix> { url = https://cache.nixos.org/nar/0nwi996rgq4b914qyx0mv2wq4k80hjac7xilikavagw7kxmn2iiv.nar.xz; sha256 = "0nwi996rgq4b914qyx0mv2wq4k80hjac7xilikavagw7kxmn2iiv"; }'

now runs in 17 MiB (was 70 MiB), while

  nix-build --store ~/my-nix/ -E 'import <nix/fetchurl.nix> { url = https://cache.nixos.org/nar/0nwi996rgq4b914qyx0mv2wq4k80hjac7xilikavagw7kxmn2iiv.nar.xz; sha256 = "0d2fxljdih3nc5dqx41hjzic3141ajil94m8kdbpryq569dpsbvb"; unpack = true; }'

runs in 17 MiB (was 346 MiB).
2018-05-30 13:42:51 +02:00
Eelco Dolstra
08ec757726
Make LocalBinaryCacheStore::narFromPath() run in constant memory
This reduces memory consumption of

  nix copy --from file://... --to ~/my-nix /nix/store/95cwv4q54dc6giaqv6q6p4r02ia2km35-blender-2.79

from 514 MiB to 18 MiB for an uncompressed binary cache, and from 192
MiB to 53 MiB for a bzipped binary cache. It may also be faster
because fetching can happen concurrently with decompression/writing.

Continuation of 48662d151b.

Issue https://github.com/NixOS/nix/issues/1681.
2018-05-30 13:34:57 +02:00
Eelco Dolstra
81ea8bd5ce
Simplify the callback mechanism 2018-05-30 13:34:37 +02:00
Eelco Dolstra
737ed88f35
Modularize config settings
Allow global config settings to be defined in multiple Config
classes. For example, this means that libutil can have settings and
evaluator settings can be moved out of libstore. The Config classes
are registered in a new GlobalConfig class to which config files
etc. are applied.

Relevant to https://github.com/NixOS/nix/issues/2009 in that it
removes the need for ad hoc handling of useCaseHack, which was the
underlying cause of that issue.
2018-05-30 13:28:01 +02:00
Will Dietz
b08923b4a0 serialise: fix buffer size used, hide method for internal use only
Fixes #2169.
2018-05-21 17:30:38 -05:00
Eelco Dolstra
53ec5ac69f
Fix some random -Wconversion warnings 2018-05-02 13:56:34 +02:00
Eelco Dolstra
4a2c948943
Fix bzip2 compression of files > 4 GiB
Bzip2's 'avail_in' parameter is declared as an unsigned int, so
assigning a size_t length to it led to silent truncation.

Fixes #2111.
2018-05-02 12:54:30 +02:00
Eelco Dolstra
28eb9621cc
Fix build 2018-03-22 13:46:19 +01:00
Eelco Dolstra
dce8af59a6
Tweak 2018-03-22 13:32:18 +01:00
Eelco Dolstra
f87e286e82
Merge branch 'fix/avoid-large-stack-buffers' of https://github.com/dtzWill/nix 2018-03-22 13:19:25 +01:00
Eelco Dolstra
47f7e5585b Make 'nix copy --from ssh://...' run in constant memory
For instance, this reduced the memory consumption of

  $ nix copy --from ssh://localhost --to ~/my-nix /nix/store/1n7x0yv8vq6zi90hfmian84vdhd04bgp-blender-2.79a

from 632 MiB to 16 MiB.
2018-03-21 23:10:40 +01:00
Eelco Dolstra
1aca195e52
Hack to get SSH error messages from build-remote
E.g.

  cannot build on 'ssh://mac1': cannot connect to 'mac1': bash: nix-store: command not found
  cannot build on 'ssh://mac2': cannot connect to 'mac2': Host key verification failed.
  cannot build on 'ssh://mac3': cannot connect to 'mac3': Received disconnect from 213... port 6001:2: Too many authentication failures
  Authentication failed.
2018-03-20 15:25:26 +01:00
Will Dietz
f5a2136a40 serialise.cc: remove pessimising move
from clang6:

src/libutil/serialise.cc:189:23: warning: moving a temporary object prevents copy elision [-Wpessimizing-move]
2018-03-19 19:18:47 -05:00
Will Dietz
9b33201e72 util: rename stdout/stdin members to avoid conflicts w/standard macro
(cherry picked from commit c389a7fb617ed7bcd617efa68c6a48c00405310d)
2018-03-19 11:18:56 -05:00
Eelco Dolstra
48662d151b
Reduce substitution memory consumption
copyStorePath() now pipes the output of srcStore->narFromPath()
directly into dstStore->addToStore(). The sink used by the former is
converted into a source usable by the latter using
boost::coroutine2. This is based on [1].

This reduces the maximum resident size of

  $ nix build --store ~/my-nix/ /nix/store/b0zlxla7dmy1iwc3g459rjznx59797xy-binutils-2.28.1 --substituters file:///tmp/binary-cache-xz/ --no-require-sigs

from 418592 KiB to 53416 KiB. (The previous commit also reduced the
runtime from ~4.2s to ~3.4s, not sure why.) A further improvement will
be to download files into a Sink.

[1] https://github.com/NixOS/nix/compare/master...Mathnerd314:dump-fix-coroutine#diff-dcbcac55a634031f9cc73707da6e4b18

Issue #1969.
2018-03-16 20:35:59 +01:00
Eelco Dolstra
3e6b194d78
decompress(): Use a Source and Sink
This allows decompression to happen in O(1) memory.
2018-03-16 20:35:59 +01:00
Eelco Dolstra
4868721506
Filter ANSI colors when not writing to a terminal
Fixes https://github.com/NixOS/nixpkgs/issues/37114.
2018-03-15 16:08:07 +01:00
Eelco Dolstra
7b8914825a
Merge pull request #1965 from masaeedu/master
Wrap thread local in function for Cygwin
2018-03-15 14:56:21 +01:00
Shea Levy
cfdbfa6b2c
Catch more possible instances of passing NULL to memcpy.
Actually fixes #1976.
2018-03-14 23:53:43 -04:00
Asad Saeeduddin
be54f4a0b6 Wrap thread local in function for Cygwin
Fixes #1826. See #1352 for a previous instance of a similar change.
2018-03-12 00:56:41 -04:00
Eelco Dolstra
24b739817f
Fix double free in Store::queryPathInfo()
It was holding on to a Value* (i.e. a std::shared_ptr<ValidPathInfo>*)
outside of the pathInfoCache lock, so the std::shared_ptr could be
destroyed between the release of the lock and the decrement of the
std::shared_ptr refcount. This can happen if more than
'path-info-cache-size' paths are added in the meantime, *or* if
clearPathInfoCache() is called. The hydra-queue-runner queue monitor
thread periodically calls the later, so is likely to trigger a crash.

Fixes https://github.com/NixOS/hydra/issues/542.
2018-03-09 14:19:51 +01:00
Will Dietz
e917c05628 logging: Don't throw from Activity destructor
Move definition of destructor to logging.cc for
access to util.hh's ignoreException.
2018-03-06 10:42:58 -06:00
Will Dietz
c89a3d5368 don't allocate large buffers on the stack 2018-03-02 10:52:04 -06:00
Shea Levy
aa8bbbf69d
Merge branch 'write-failure-fixes' of git://github.com/lheckemann/nix 2018-03-02 10:59:59 -05:00
Eelco Dolstra
24ec750003
nix run: Fix segfault on macOS
Note that clearenv() is not available on macOS.

Fixes #1907.
2018-02-26 18:29:40 +01:00
Tuomas Tynkkynen
546f98dace libutil: Fix invalid assert on decoding base64 hashes
The assertion is broken because there is no one-to-one mapping from
length of a base64 string to the length of the output.

E.g.

"1q69lz7Empb06nzfkj651413n9icx0njmyr3xzq1j9q=" results in a 32-byte output.
"1q69lz7Empb06nzfkj651413n9icx0njmyr3xzq1j9qy" results in a 33-byte output.

To reproduce, evaluate:

builtins.derivationStrict {
    name = "0";
    builder = "0";
    system = "0";
    outputHashAlgo = "sha256";
    outputHash = "1q69lz7Empb06nzfkj651413n9icx0njmyr3xzq1j9qy";
}

Found by afl-fuzz.
2018-02-19 23:20:26 +02:00
Tuomas Tynkkynen
1d0e42879f libutil: Fix infinite loop in filterANSIEscapes on '\r'
E.g. nix-instantiate --eval -E 'abort "\r"' hangs.

Found by afl-fuzz.
2018-02-19 23:20:26 +02:00
Eelco Dolstra
ed73d40c3b
Config::handleUnknownSettings(): Remove unused 'fatal' argument 2018-02-19 14:00:34 +01:00
Eelco Dolstra
75a1d96cfd
Merge branch 'register-settings' of https://github.com/shlevy/nix 2018-02-19 13:58:34 +01:00
Eelco Dolstra
7fe5910bf8
Merge pull request #1857 from dtzWill/fix/check-for-lzma-mt
configure.ac: check if lzma has MT support, fix deb build/etc.
2018-02-19 13:06:14 +01:00
Shea Levy
ac973a6d3c
monitor-fds: Fix on macOS.
Fixes #1871.
2018-02-14 18:26:37 -05:00
Shea Levy
de4934ab3b
Allow plugins to define new settings. 2018-02-13 14:43:32 -05:00
Linus Heckemann
78ac3eb4eb Fix #1762
nix-store --export, nix-store --dump, and nix dump-path would previously
fail silently if writing the data out failed, because
 a) FdSink::write ignored exceptions, and
 b) the commands relied on FdSink's destructor, which ignores
    exceptions, to flush the data out.

This could cause rather opaque issues with installing nixos, because
nix-store --export would happily proceed even if it couldn't write its
data out (e.g. if nix-store --import on the other side of the pipe
failed).

This commit adds tests that expose these issues in the nix-store
commands, and fixes them for all three.
2018-02-13 14:26:19 +00:00
Shea Levy
6eb1040e90
Allow includes from nix.conf 2018-02-13 08:16:32 -05:00
Will Dietz
c6209030c4 compression: make parallel sink separate class 2018-02-11 13:50:28 -06:00
Will Dietz
a0bdc96726 compression: print warning if parallel requested but not supported 2018-02-11 13:03:47 -06:00
Will Dietz
5a082ad15a configure.ac: check if lzma has MT support, fix deb build/etc. 2018-02-09 21:02:25 -06:00
AmineChikhaoui
55ecdfe2a8
make multi threaded compression configurable and use single threaded
by default.
2018-02-07 17:54:08 +01:00
AmineChikhaoui
163e39547a
Merge branch 'master' of https://github.com/NixOS/nix into parallel-xz 2018-02-07 17:53:50 +01:00
Eelco Dolstra
84989d3af2
Improve filtering of ANSI escape sequences in build logs
All ANSI sequences except color setting are now filtered out. In
particular, terminal resets (such as from NixOS VM tests) are filtered
out.

Also, fix the completely broken tab character handling.
2018-02-07 15:23:57 +01:00
AmineChikhaoui
9d1e22f743
set block size to 0 to let the lzma lib choose the right one, add
some comments about possible improvements wrt memory usage/threading.
2018-02-07 11:18:55 +01:00
AmineChikhaoui
bc7e3a4dd6
support multi threaded xz encoder, this might be particularly useful in
the case of hydra where the overhead of single threaded encoding is more
noticeable e.g most of the time spent in "Sending inputs"/"Receiving outputs"
is due to compression while the actual upload to the binary cache seems
to be negligible.
2018-02-06 22:42:02 +01:00
Eelco Dolstra
d4dcffd643
Add pure evaluation mode
In this mode, the following restrictions apply:

* The builtins currentTime, currentSystem and storePath throw an
  error.

* $NIX_PATH and -I are ignored.

* fetchGit and fetchMercurial require a revision hash.

* fetchurl and fetchTarball require a sha256 attribute.

* No file system access is allowed outside of the paths returned by
  fetch{Git,Mercurial,url,Tarball}. Thus 'nix build -f ./foo.nix' is
  not allowed.

Thus, the evaluation result is completely reproducible from the
command line arguments. E.g.

  nix build --pure-eval '(
    let
      nix = fetchGit { url = https://github.com/NixOS/nixpkgs.git; rev = "9c927de4b179a6dd210dd88d34bda8af4b575680"; };
      nixpkgs = fetchGit { url = https://github.com/NixOS/nixpkgs.git; ref = "release-17.09"; rev = "66b4de79e3841530e6d9c6baf98702aa1f7124e4"; };
    in (import (nix + "/release.nix") { inherit nix nixpkgs; }).build.x86_64-linux
  )'

The goal is to enable completely reproducible and traceable
evaluation. For example, a NixOS configuration could be fully
described by a single Git commit hash. 'nixos-rebuild' would do
something like

  nix build --pure-eval '(
    (import (fetchGit { url = file:///my-nixos-config; rev = "..."; })).system
  ')

where the Git repository /my-nixos-config would use further fetchGit
calls or Git externals to fetch Nixpkgs and whatever other
dependencies it has. Either way, the commit hash would uniquely
identify the NixOS configuration and allow it to reproduced.
2018-01-16 19:23:18 +01:00
Will Dietz
9dd2b8ac7b use libbrotli directly when available
* Look for both 'brotli' and 'bro' as external command,
  since upstream has renamed it in newer versions.
  If neither are found, current runtime behavior
  is preserved: try to find 'bro' on PATH.
* Limit amount handed to BrotliEncoderCompressStream
  to ensure interrupts are processed in a timely manner.
  Testing shows negligible performance impact.
  (Other compression sinks don't seem to require this)
2017-12-30 20:26:33 -06:00
Will Dietz
e4d43f1f94 logging.cc: add missing 'override' 2017-12-11 12:08:40 -06:00
Eelco Dolstra
6cdaa858d0
Propagate flags like --sandbox to the daemon properly 2017-11-21 18:50:56 +01:00
Eelco Dolstra
d0b88db441
Cleanup 2017-11-20 17:32:58 +01:00
Eelco Dolstra
72804dc0bd
Merge pull request #1645 from twhitehead/stat-race
Fix (highly unlikely) race condition in readLink
2017-11-20 17:32:27 +01:00
Eelco Dolstra
e026bc3b05
fetchMercurial: Don't fetch hashes we already have 2017-11-01 18:43:11 +01:00
Eelco Dolstra
72cd52c3cd
builtins.fetchgit: Support importing a working tree
For example, you can write

  src = fetchgit ./.;

and if ./. refers to an unclean working tree, that tree will be copied
to the Nix store. This removes the need for "cleanSource".
2017-10-30 19:59:25 +01:00
Tyson Whitehead
07d2c6d213
Fix (highly unlikely) race condition in readLink
Used to determine symlink size with stat and value with readlink.
This could technically result in garbage if symlink changed between
calls.  Also gets around the broken stat implementation in our
network filesystem (returns size + 1 giving a byte of garbage).
2017-10-30 11:49:55 -04:00
Eelco Dolstra
2d5b1b24bf
Pass lists/attrsets to bash as (associative) arrays 2017-10-25 13:01:50 +02:00
Eelco Dolstra
96051dd057
More progress indicator improvements
Fixes #1599.
2017-10-24 14:47:23 +02:00
Eelco Dolstra
fe9d2f974d
Handle log messages from build-remote
This makes the progress indicator show statuses like "connecting to
'root@machine'".
2017-10-24 14:05:22 +02:00
Eelco Dolstra
0d59f1ca49
nix: Respect -I, --arg, --argstr
Also, random cleanup to argument handling.
2017-10-24 12:58:34 +02:00
Eelco Dolstra
37fbfffd8e
Pass all settings to build-remote
This ensures that command line flags such as --builders get passed
correctly.
2017-10-23 20:50:28 +02:00
Eelco Dolstra
fda7b95cb0
Fix a hang in ThreadPool
The worker threads could exit prematurely if they finished processing
all items while the main thread was still adding items. In particular,
this caused hanging nix-store --serve processes in the build farm.

Also, process items from the main thread.
2017-10-09 15:41:09 +02:00
Eelco Dolstra
e350671737
Doh 2017-09-25 13:25:55 +02:00
Eelco Dolstra
89dc62c174
RemoteStore: Add option to drop old connections from the pool
This is a hack to make hydra-queue-runner free its temproots
periodically, thereby ensuring that garbage collection of the
corresponding paths is not blocked until the queue runner is
restarted.

It would be better if temproots could be released earlier than at
process exit. I started working on a RAII object returned by functions
like addToStore() that releases temproots. However, this would be a
pretty massive change so I gave up on it for now.
2017-09-14 18:10:38 +02:00
Eelco Dolstra
970366266b
Add "nix add-to-store" command 2017-09-14 13:29:33 +02:00
Eelco Dolstra
b7376edf06
ThreadPool: On exception, interrupt the other worker threads 2017-09-08 15:31:24 +02:00
Eelco Dolstra
8f6b347abd
ThreadPool: Improve exception handling
In particular, process() won't return as long as there are active
items. This prevents work item lambdas from referring to stack frames
that no longer exist.
2017-09-08 14:42:09 +02:00
Eelco Dolstra
dff440aab3
nix build: Add --out-link and --no-link options 2017-09-06 16:20:34 +02:00
Eelco Dolstra
fd73c1e20a
Add an activity for binary cache queries 2017-08-31 15:25:58 +02:00
Eelco Dolstra
9f47eac92b
Fix mismatched tag warning
https://hydra.nixos.org/build/59649086
2017-08-31 11:04:52 +02:00
Eelco Dolstra
5cc8609e30
nix run: Allow passing a command to execute
E.g.

  nix run nixpkgs.hello -c hello --greeting Hallo

Note that unlike "nix-shell --command", no quoting of arguments is
necessary.

"-c" (short for "--command") cannot be combined with "--" because they
both consume all remaining arguments. But since installables shouldn't
start with a dash, this is unlikely to cause problems.
2017-08-29 14:42:48 +02:00
Eelco Dolstra
05c45f301d
readLink(): Handle symlinks in /proc
Symlinks like /proc/self/exe report a stat() size of 0, so use a
buffer of at least PATH_MAX instead.
2017-08-29 11:52:34 +02:00
Eelco Dolstra
2cc345b95f
Give activities a verbosity level again
And print them (separately from the progress bar) given sufficient -v
flags.
2017-08-28 19:13:24 +02:00
Eelco Dolstra
fe34b91289
Tunnel progress messages from the daemon to the client
This makes the progress bar work for non-root users.
2017-08-28 18:49:42 +02:00
Eelco Dolstra
e681b1f064
Simplify 2017-08-28 14:30:35 +02:00
Eelco Dolstra
94a0548dc4
Simplify 2017-08-25 21:26:37 +02:00
Eelco Dolstra
0ac35b67b8
Allow derivations to update the build phase
So the progress bar can show

  [1/0/1 built, 0.0 MiB DL] building hello-2.10 (configuring): checking whether pread is declared without a macro... yes
2017-08-25 18:04:05 +02:00
Eelco Dolstra
c137c0a5eb
Allow activities to be nested
In particular, this allows more relevant activities ("substituting X")
to supersede inferior ones ("downloading X").
2017-08-25 17:49:40 +02:00
Eelco Dolstra
db1d45037c
Handle SIGWINCH 2017-08-25 15:59:03 +02:00
Eelco Dolstra
a3015db6c3
Typo 2017-08-25 15:59:03 +02:00
Eelco Dolstra
0e9ddcc306
Restore activity metadata
This allows the progress bar to display "building perl-5.22.3" instead
of "building /nix/store/<hash>-perl-5.22.3.drv".
2017-08-25 15:58:35 +02:00
Eelco Dolstra
9400cb36b7
Disallow accidental copy construction 2017-08-21 12:18:42 +02:00
Andy Wingo
6bb4e3e8fe Remove unused decodeOctalEscaped
Besides being unused, this function has a bug that it will incorrectly
decode the path component Ubuntu\04016.04.2\040LTS\040amd64 as
"Ubuntu.04.2 LTS amd64" instead of "Ubuntu 16.04.2 LTS amd64".
2017-08-18 11:07:00 +02:00
Eelco Dolstra
c2cab20732
nix verify: Restore the progress indicator 2017-08-16 20:56:03 +02:00
Eelco Dolstra
b4ed97e3a3
nix optimise-store: Show how much space has been freed 2017-08-16 20:56:03 +02:00
Eelco Dolstra
23b8b7e096
nix optimise-store: Add
This replaces "nix-store --optimise". Main difference is that it has a
progress indicator.
2017-08-16 20:56:03 +02:00
Eelco Dolstra
40bffe0a43
Progress indicator: Cleanup 2017-08-16 20:56:03 +02:00
Eelco Dolstra
dff12b38f9
Progress indicator: More improvements 2017-08-16 20:56:03 +02:00
Eelco Dolstra
bf1f123b09
Progress indicator: Show number of active items 2017-08-16 20:56:03 +02:00
Eelco Dolstra
0e0dcf2c7e
Progress indicator: Unify "copying" and "substituting"
They're the same thing after all.

Example:

  $ nix build --store local?root=/tmp/nix nixpkgs.firefox-unwrapped
  [0/1 built, 49/98 copied, 16.3/92.8 MiB DL, 55.8/309.2 MiB copied] downloading 'https://cache.nixos.org/nar/0pl9li1jigcj2dany47hpmn0r3r48wc4nz48v5mqhh426lgz3bz6.nar.xz'
2017-08-16 20:56:03 +02:00
Eelco Dolstra
c36467ad2e
Improve substitution progress indicator
E.g.

  $ nix build --store local?root=/tmp/nix nixpkgs.firefox-unwrapped
  [0/1 built, 1/97/98 fetched, 65.8/92.8 MiB DL, 203.2/309.2 MiB copied] downloading 'https://cache.nixos.org/nar/1czm9fk0svacy4h6a3fzkpafi4f7a9gml36kk8cq1igaghbspg3k.nar.xz'
2017-08-16 20:56:02 +02:00
Eelco Dolstra
b29b6feaba
nix copy: Improve progress indicator
It now shows the amount of data copied:

  [8/1038 copied, 160.4/1590.9 MiB copied] copying path '...'
2017-08-16 20:56:02 +02:00
Eelco Dolstra
c5e4404580
nix copy: Revive progress bar 2017-08-16 20:56:02 +02:00
Eelco Dolstra
af765a8eab
Use /proc/self/fd to efficiently close all FDs on Linux
Issue #1506.
2017-08-09 16:22:05 +02:00
Brian McKenna
b39cc4fc81 Include missing <cstdlib> for abort()
This is needed to get Nix compiled using Android NDK.
2017-08-03 07:03:22 +10:00
Eelco Dolstra
a2778988f2
Merge branch 'macOS' of https://github.com/davidak/nix 2017-07-31 10:31:51 +02:00
Jörg Thalheim
2fd8f8bb99 Replace Unicode quotes in user-facing strings by ASCII
Relevant RFC: NixOS/rfcs#4

$ ag -l | xargs sed -i -e "/\"/s/’/'/g;/\"/s/‘/'/g"
2017-07-30 12:32:45 +01:00
davidak
92bcb61127 replace "Mac OS X" with "macOS"
except in older release notes where the name was actually Mac OS X.
2017-07-30 12:26:17 +02:00
Eelco Dolstra
af4689f9e9
nix-prefetch-url: Fix regression in hash printing 2017-07-28 14:56:39 +02:00
Eelco Dolstra
57b9505731
nix search: Add a cache
The package list is now cached in
~/.cache/nix/package-search.json. This gives a substantial speedup to
"nix search" queries. For example (on an SSD):

First run: (no package search cache, cold page cache)

  $ time nix search blender
  Attribute name: nixpkgs.blender
  Package name: blender
  Version: 2.78c
  Description: 3D Creation/Animation/Publishing System

  real    0m6.516s

Second run: (package search cache populated)

  $ time nix search blender
  Attribute name: nixpkgs.blender
  Package name: blender
  Version: 2.78c
  Description: 3D Creation/Animation/Publishing System

  real    0m0.143s
2017-07-26 17:29:10 +02:00
Eelco Dolstra
90825dea51
Add "nix search" command 2017-07-20 13:33:13 +02:00
Eelco Dolstra
112ff7833d
nix: Show help when no arguments are given
Fixes #1464.
2017-07-14 13:44:45 +02:00