Commit graph

775 commits

Author SHA1 Message Date
Eelco Dolstra 0e459d79a6
Merge branch 'issue-3147-inNixShell-arg' of https://github.com/hercules-ci/nix 2019-10-27 17:10:19 +01:00
Robert Hensing 9d612c393a Add inNixShell = true to nix-shell auto-call
This is an alternative to the IN_NIX_SHELL environment variable,
allowing the expression to adapt itself to nix-shell without
triggering those adaptations when used as a dependency of another
shell.

Closes #3147
2019-10-27 13:16:02 +01:00
Eelco Dolstra e012384fe9
Merge branch 'tojson-tostring-fix' of https://github.com/mayflower/nix 2019-10-27 12:18:35 +01:00
Robin Gloster e583df5280
builtins.toJSON: fix __toString usage 2019-10-27 10:15:51 +01:00
Eelco Dolstra aabf5c86c9
Add experimental-features setting
Experimental features are now opt-in. There is currently one
experimental feature: "nix-command" (which enables the "nix"
command. This will allow us to merge experimental features more
quickly, without committing to supporting them indefinitely.

Typical usage:

$ nix build --experimental-features 'nix-command flakes' nixpkgs#hello

(cherry picked from commit 8e478c2341,
without the "flakes" feature)
2019-10-21 13:34:44 +02:00
Eelco Dolstra 9348f9291e
nix-env: Create ~/.nix-profile automatically 2019-10-09 23:35:01 +02:00
Eelco Dolstra 26762ceb86
nix-profile.sh: Don't create .nix-channels
This is already done by the installer, so no need to do it again.
2019-10-09 23:35:01 +02:00
Eelco Dolstra 5a303093dc
Remove world-writability from per-user directories
'nix-daemon' now creates subdirectories for users when they first
connect.

Fixes #509 (CVE-2019-17365).
Should also fix #3127.
2019-10-09 23:34:48 +02:00
Jonas Chevalier 619cc4af85
function-trace: always show the trace
If the user invokes nix with --trace-function-calls it means that they
want to see the trace.
2019-09-18 23:23:21 +02:00
Eelco Dolstra 5fad9d01c2
gc-auto.sh: Increase sleep time 2019-09-04 12:52:54 +02:00
Eelco Dolstra 08ee364950
gc-auto.sh: More test fixes 2019-09-03 18:11:43 +02:00
Eelco Dolstra cec50290bf
gc-auto.sh: Add some more instrumentation 2019-09-03 15:45:32 +02:00
Eelco Dolstra a2c4fcd5e9 Don't rely on st_blocks
It doesn't seem very reliable on ZFS.
2019-08-29 14:49:58 +02:00
Eelco Dolstra 31f5ecfaa5 Maybe fix #3058 2019-08-29 12:35:15 +02:00
Eelco Dolstra ecb0a23d51 Add some more instrumentation 2019-08-29 12:10:01 +02:00
Eelco Dolstra b6120d26a8
gc-auto.sh: Increase verbosity 2019-08-28 22:19:31 +02:00
Eelco Dolstra 73728874ab Hopefully fix post-hook test on macOS
https://hydra.nixos.org/build/99262744
2019-08-27 17:01:54 +02:00
Eelco Dolstra 477f82e5a7
Merge pull request #2782 from grahamc/flames
Track function start and end
2019-08-15 14:20:42 +02:00
Graham Christensen ee9c988a1b
Track function start and ends for flame graphs
With this patch, and this file I called `log.py`:

    #!/usr/bin/env nix-shell
    #!nix-shell -i python3 -p python3 --pure

    import sys
    from pprint import pprint

    stack = []
    timestack = []

    for line in open(sys.argv[1]):
        components = line.strip().split(" ", 2)
        if components[0] != "function-trace":
            continue

        direction = components[1]
        components = components[2].rsplit(" ", 2)

        loc = components[0]
        _at = components[1]
        time = int(components[2])

        if direction == "entered":
            stack.append(loc)
            timestack.append(time)
        elif direction == "exited":
            dur = time - timestack.pop()
            vst = ";".join(stack)
            print(f"{vst} {dur}")
            stack.pop()

and:

    nix-instantiate --trace-function-calls -vvvv ../nixpkgs/pkgs/top-level/release.nix -A unstable > log.matthewbauer 2>&1
    ./log.py ./log.matthewbauer > log.matthewbauer.folded
    flamegraph.pl --title matthewbauer-post-pr log.matthewbauer.folded > log.matthewbauer.folded.svg

I can make flame graphs like: http://gsc.io/log.matthewbauer.folded.svg

---

Includes test cases around function call failures and tryEval. Uses
RAII so the finish is always called at the end of the function.
2019-08-14 16:09:35 -04:00
Eelco Dolstra 05a10dd835
tests/post-hook.sh: Don't put result link in cwd 2019-08-08 15:47:56 +02:00
Eelco Dolstra 2053ac7747
Rename file for consistency 2019-08-08 12:18:46 +02:00
Eelco Dolstra 56df30cd3f
Merge pull request #2995 from tweag/post-build-hook
Add a post build hook
2019-08-07 15:02:29 +02:00
Eelco Dolstra ec415d7166
Add a test for auto-GC
This currently fails because we're using POSIX file locks. So when the
garbage collector opens and closes its own temproots file, it causes
the lock to be released and then deleted by another GC instance.
2019-08-02 18:39:16 +02:00
regnat 7c5596734f
Add a post-build-hook
Passing `--post-build-hook /foo/bar` to a nix-* command will cause
`/foo/bar` to be executed after each build with the following
environment variables set:

    DRV_PATH=/nix/store/drv-that-has-been-built.drv
    OUT_PATHS=/nix/store/...build /nix/store/...build-bin /nix/store/...build-dev

This can be useful in particular to upload all the builded artifacts to
the cache (including the ones that don't appear in the runtime closure
of the final derivation or are built because of IFD).

This new feature prints the stderr/stdout output to the `nix-build`
and `nix build` client, and the output is printed in a Nix 2
compatible format:

    [nix]$ ./inst/bin/nix-build ./test.nix
    these derivations will be built:
      /nix/store/ishzj9ni17xq4hgrjvlyjkfvm00b0ch9-my-example-derivation.drv
    building '/nix/store/ishzj9ni17xq4hgrjvlyjkfvm00b0ch9-my-example-derivation.drv'...
    hello!
    bye!
    running post-build-hook '/home/grahamc/projects/github.com/NixOS/nix/post-hook.sh'...
    post-build-hook: + sleep 1
    post-build-hook: + echo 'Signing paths' /nix/store/qr213vjmibrqwnyp5fw678y7whbkqyny-my-example-derivation
    post-build-hook: Signing paths /nix/store/qr213vjmibrqwnyp5fw678y7whbkqyny-my-example-derivation
    post-build-hook: + sleep 1
    post-build-hook: + echo 'Uploading paths' /nix/store/qr213vjmibrqwnyp5fw678y7whbkqyny-my-example-derivation
    post-build-hook: Uploading paths /nix/store/qr213vjmibrqwnyp5fw678y7whbkqyny-my-example-derivation
    post-build-hook: + sleep 1
    post-build-hook: + printf 'very important stuff'
    /nix/store/qr213vjmibrqwnyp5fw678y7whbkqyny-my-example-derivation

    [nix-shell:~/projects/github.com/NixOS/nix]$ ./inst/bin/nix build -L -f ./test.nix
    my-example-derivation> hello!
    my-example-derivation> bye!
    my-example-derivation (post)> + sleep 1
    my-example-derivation (post)> + echo 'Signing paths' /nix/store/c263gzj2kb2609mz8wrbmh53l14wzmfs-my-example-derivation
    my-example-derivation (post)> Signing paths /nix/store/c263gzj2kb2609mz8wrbmh53l14wzmfs-my-example-derivation
    my-example-derivation (post)> + sleep 1
    my-example-derivation (post)> + echo 'Uploading paths' /nix/store/c263gzj2kb2609mz8wrbmh53l14wzmfs-my-example-derivation
    my-example-derivation (post)> Uploading paths /nix/store/c263gzj2kb2609mz8wrbmh53l14wzmfs-my-example-derivation
    my-example-derivation (post)> + sleep 1
    my-example-derivation (post)> + printf 'very important stuff'
    [1 built, 0.0 MiB DL]

Co-authored-by: Graham Christensen <graham@grahamc.com>
Co-authored-by: Eelco Dolstra <edolstra@gmail.com>
2019-08-02 10:48:15 -04:00
Eelco Dolstra 219d645987
Merge pull request #3013 from basvandijk/disable-lsof-for-darwin-tests
Disable findRuntimeRoots on darwin when running tests because lsof is slow
2019-07-30 11:34:18 +02:00
Bas van Dijk ee1e3132ca Disable findRuntimeRoots on darwin when running tests because lsof is slow
See: https://github.com/NixOS/nix/issues/3011
2019-07-30 11:29:03 +02:00
Bas van Dijk 89865144c3 Allow builtins.pathExists to check the existence of /nix/store paths
This makes it consitent with builtins.readDir.
2019-07-30 11:27:35 +02:00
Matthew Bauer 03addc3b0a Use $HOME instead of $USER
$USER/.nix-profile will not be a path. I think $HOME/.nix-profile was
the origininal intent.

/cc @Grahamc
2019-07-25 09:44:01 -04:00
Graham Christensen 68bdd83dc8
timeout: test for error code 2019-07-02 11:18:36 -04:00
Daiderd Jordan a52c331edb
build: replace 100 offset for build exit codes 2019-07-02 00:12:38 +02:00
Daiderd Jordan 99ee3755dd
build: add tests for --check status codes 2019-07-02 00:12:38 +02:00
Eelco Dolstra 94f11d0a61
Fix abort in fromTOML
Fixes #2969.
2019-06-24 17:09:09 +02:00
Eelco Dolstra 99cec651c9
Add more fromTOML tests 2019-06-24 16:52:11 +02:00
Eelco Dolstra 5064971ded
Fix test failures when $TMPDIR changes
(cherry picked from commit c38c726eb5)
2019-06-15 16:36:33 +02:00
Eelco Dolstra aec545c20b Fix segfault in builtin fetchurl with hashed mirrors + SRI hashes 2019-06-01 15:27:43 +02:00
Eelco Dolstra 17ef3e6f41
Enable more fromTOML tests
cpptoml now parses almost all examples from the spec.
2019-05-29 12:22:52 +02:00
Eelco Dolstra cfd74aef1e
Fix eval-okay-fromTOML test
Turns out we were mis-parsing single-quoted attributes, e.g. 'key2'.
2019-05-29 12:12:02 +02:00
Eelco Dolstra 9eaebbf575
Merge branch 'attrPaths' of https://github.com/NinjaTrappeur/nix 2019-05-28 22:59:05 +02:00
Daiderd Jordan d75bdb5793
build: add test for sandboxed --check 2019-05-12 16:46:21 +02:00
Will Dietz a834861876
fix hashfile test that wasn't failing due to eval laziness
See:
7becb1bf1c (r33450554)
2019-05-08 10:04:54 +02:00
Daniel Schaefer 3f192ac80c Add builtins.hashFile
For text files it is possible to do it like so:
`builtins.hashString "sha256" (builtins.readFile /tmp/a)`
but that doesn't work for binary files.

With builtins.hashFile any kind of file can be conveniently hashed.
2019-05-03 17:23:36 +02:00
Eelco Dolstra e489f5cabf Update eval-okay-types.exp to match #1828 2019-03-27 21:07:04 +01:00
Jonas Chevalier 514b3c7f83
Add isPath primop
this is added for completeness' sake since all the other possible
`builtins.typeOf` results have a corresponding `builtins.is<Type>`
2019-03-24 11:36:49 +01:00
Guillaume Maudoux 115e2c8c67 Update tests to the new --roots format 2019-03-10 01:50:33 +01:00
Eelco Dolstra b71e1fb342
Restore --init calls in tests 2019-03-04 18:27:45 +08:00
Jonas Chevalier b402148d8f
remove noop uses of nix-store --init
the nix-store --init command is a noop apparently
2019-02-22 21:07:53 +01:00
Shea Levy b30be6b450
Add builtins.appendContext.
A partner of builtins.getContext, useful for the same reasons.
2019-01-31 08:52:23 -05:00
Shea Levy 1d757292d0
Add builtins.getContext.
This can be very helpful when debugging, as well as enabling complex
black magic like surgically removing a single dependency from a
string's context.
2019-01-14 11:27:10 -05:00
Will Dietz aa7e52abff tests/fetchurl: fix after changing default hash from 512 to 256 2018-12-14 22:37:20 -06:00
Eelco Dolstra 6024dc1d97
Support SRI hashes
SRI hashes (https://www.w3.org/TR/SRI/) combine the hash algorithm and
a base-64 hash. This allows more concise and standard hash
specifications. For example, instead of

  import <nix/fetchurl.nl> {
    url = https://nixos.org/releases/nix/nix-2.1.3/nix-2.1.3.tar.xz;
    sha256 = "5d22dad058d5c800d65a115f919da22938c50dd6ba98c5e3a183172d149840a4";
  };

you can write

  import <nix/fetchurl.nl> {
    url = https://nixos.org/releases/nix/nix-2.1.3/nix-2.1.3.tar.xz;
    hash = "sha256-XSLa0FjVyADWWhFfkZ2iKTjFDda6mMXjoYMXLRSYQKQ=";
  };

In fixed-output derivations, the outputHashAlgo is no longer mandatory
if outputHash specifies the hash (either as an SRI or in the old
"<type>:<hash>" format).

'nix hash-{file,path}' now print hashes in SRI format by default. I
also reverted them to use SHA-256 by default because that's what we're
using most of the time in Nixpkgs.

Suggested by @zimbatm.
2018-12-13 14:30:52 +01:00
Eelco Dolstra 3f4de91d80
Merge branch 'better-git-cache' of https://github.com/graham-at-target/nix 2018-11-20 20:41:19 +01:00
Eelco Dolstra 812e39313c
Enable sandboxing by default
Closes #179.
2018-11-07 17:08:28 +01:00
Eelco Dolstra 18b4c53f71
Restore old (dis)allowedRequisites behaviour for self-references
stdenv relies on this. So ignore self-references (but only in legacy non-structured attributes mode).
2018-10-27 15:41:53 +02:00
Eelco Dolstra 3cd15c5b1f
Per-output reference and closure size checks
In structured-attributes derivations, you can now specify per-output
checks such as:

  outputChecks."out" = {
    # The closure of 'out' must not be larger than 256 MiB.
    maxClosureSize = 256 * 1024 * 1024;

    # It must not refer to C compiler or to the 'dev' output.
    disallowedRequisites = [ stdenv.cc "dev" ];
  };

  outputChecks."dev" = {
    # The 'dev' output must not be larger than 128 KiB.
    maxSize = 128 * 1024;
  };

Also fixed a bug in allowedRequisites that caused it to ignore
self-references.
2018-10-23 01:29:16 +02:00
Eelco Dolstra 01bd66bf83
Merge pull request #2452 from ElvishJerricco/verify-sigs-overflow
Fix overflow when verifying signatures of content addressable paths
2018-10-08 12:03:03 +02:00
Eelco Dolstra 1e7b8deea7
Check requiredSystemFeatures for local builds
For example, this prevents a "kvm" build on machines that don't have
KVM.

Fixes #2012.
2018-09-28 16:10:27 +02:00
Will Fancher b7091ce41e Add a test for signed content-addressed paths 2018-09-25 22:18:52 -04:00
Graham Christensen 0aca1ffb6e Prefer 'remote builder' over 'slave' 2018-09-10 18:57:46 +02:00
Eelco Dolstra 9b1bdf2db8
FIx floating point evaluation
Fixes #2361.
2018-08-19 11:59:49 +02:00
Graham Christensen 02098d2073 fetchGit: use a better caching scheme
The current usage technically works by putting multiple different
repos in to the same git directory. However, it is very slow as
Git tries very hard to find common commits between the two
repositories. If the two repositories are large (like Nixpkgs and
another long-running project,) it is maddeningly slow.

This change busts the cache for existing deployments, but users
will be promptly repaid in per-repository performance.
2018-08-17 11:27:34 -04:00
Eelco Dolstra fa4def3d46
Require libbrotli 2018-08-06 14:06:54 +02:00
Eelco Dolstra 34c17fdae5
Add a test for LegacySSHStore that doesn't require a VM 2018-08-03 21:20:38 +02:00
Eelco Dolstra bc65e02d96
Merge pull request #2326 from aszlig/fix-symlink-leak
Fix symlink leak in restricted eval mode
2018-08-03 17:01:34 +02:00
aszlig 43e28a1b75
Fix symlink leak in restricted eval mode
In EvalState::checkSourcePath, the path is checked against the list of
allowed paths first and later it's checked again *after* resolving
symlinks.

The resolving of the symlinks is done via canonPath, which also strips
out "../" and "./". However after the canonicalisation the error message
pointing out that the path is not allowed prints the symlink target in
the error message.

Even if we'd suppress the message, symlink targets could still be leaked
if the symlink target doesn't exist (in this case the error is thrown in
canonPath).

So instead, we now do canonPath() without symlink resolving first before
even checking against the list of allowed paths and then later do the
symlink resolving and checking the allowed paths again.

The first call to canonPath() should get rid of all the "../" and "./",
so in theory the only way to leak a symlink if the attacker is able to
put a symlink in one of the paths allowed by restricted evaluation mode.

For the latter I don't think this is part of the threat model, because
if the attacker can write to that path, the attack vector is even
larger.

Signed-off-by: aszlig <aszlig@nix.build>
2018-08-03 06:46:43 +02:00
Samuel Dionne-Riel 438e02529d Allows selectively adding environment variables to pure shells.
Includes documentation and test.
2018-08-02 08:21:30 -04:00
volth 403a76a18f lib.concatMap and lib.mapAttrs to be builtins 2018-07-05 02:54:09 +00:00
Will Dietz cb9ef85852 tests/search.sh: minor fix to unbreak tests after search ux merge 2018-07-03 15:37:06 -05:00
Eelco Dolstra 3b1f54cf06
Add a fromTOML primop
This is primarily useful for processing Cargo.lock files.
2018-07-03 18:39:36 +02:00
Aleksandr Pashkov 5ee4472b8b tests: more robust check for user namespaces availability (canUseSandbox)
Issue https://github.com/NixOS/nix/issues/2165
2018-06-06 00:41:01 +03:00
Eelco Dolstra 4ac4f675df
Don't require --fallback to recover from disappeared binary cache NARs 2018-06-05 16:04:41 +02:00
Eelco Dolstra ca06a9cea7
Improve binary cache fallback test 2018-06-05 15:26:12 +02:00
Eelco Dolstra a936a19da3
Remove non-existent NIX_DEBUG_SUBST 2018-06-05 13:40:45 +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
volth 88c1ea30e4 add docs and tests 2018-05-24 12:51:34 +00:00
Eelco Dolstra 1ad19232c4
Don't return negative numbers from the flex tokenizer
Fixes #1374.
Closes #2129.
2018-05-11 12:05:12 +02:00
Eelco Dolstra 548ad391d9
Fix builtins.add test
Nix prints the floating point number 4.0 as "4".
2018-05-02 13:49:32 +02:00
Félix Baylac-Jacqué b2f3a7411a
nix-lang: Add deep nested mixed attrs test case. 2018-05-01 14:42:34 +02:00
Tim Sears 9a714f75af
add tests for builtins.add 2018-04-29 12:03:42 -07:00
Shea Levy e2b028353b
Merge branch 'pos-crash-fix' of git://github.com/dezgeg/nix 2018-04-23 08:43:54 -04:00
Shea Levy 0aae411eaa
Merge branch 'add-test-eval-okay-nested-with' of git://github.com/ryantrinkle/nix 2018-04-23 08:43:14 -04:00
Daniel Poelzleithner f6e8ceafa6 add tests for multi search 2018-04-18 21:45:46 +02:00
Félix Baylac-Jacqué 00584bb091
parser: Allow mixed nested and top-level attrpaths
Fixes #2077.
2018-04-18 18:44:38 +02:00
Félix Baylac-Jacqué 10d33452e2
nix-lang parser: Add mixed nested attrs tests.
Part of issue #2077
2018-04-17 09:13:01 +02:00
Shea Levy 7459388448
Merge branch 'fix/ruby-shebang' of git://github.com/samueldr/nix 2018-04-09 10:54:39 -04:00
Samuel Dionne-Riel a4c9b2595e Hardcodes nix-shell instead of /usr/bin/env nix-shell...
... in the ruby shebang test.
2018-04-09 09:36:54 -04:00
Samuel Dionne-Riel 9478f88681 Adds nix-shell test for special-cased ruby interpreter.
The test fakes the interpreter only to verify the arguments it would be
given.
2018-04-08 00:45:28 -04:00
Doug Beardsley 72902ec399 Add missing eval-okay-regex-split.exp test file 2018-04-06 12:18:59 -06:00
Tuomas Tynkkynen af86132e1a libexpr: Make unsafeGetAttrPos not crash on noPos
Currently e.g. `builtins.unsafeGetAttrPos "abort" builtins` will
eventually segfault because pos->file is an unset Symbol.

Found by afl-fuzz.
2018-04-03 15:54:42 +03:00
Ryan Trinkle f2273b11f5 Add test eval-okay-nested-with 2018-03-30 15:41:16 -04:00
Linus Heckemann 12913ccf45 nix-shell: allow symlinks to .drvs
This makes persistent shell environments easier to use.
2018-03-16 22:15:24 +00:00
Eelco Dolstra 64441f0551
Merge pull request #1939 from dezgeg/lexer-fix
libexpr: Recognize newline in more places in lexer
2018-03-16 12:14:58 +01:00
Eelco Dolstra ca14b14200
Use boost::format from the boost package
Note that this only requires headers from boost so it doesn't add a
runtime dependency.

Also, use Nixpkgs 18.03.
2018-03-14 19:24:04 +01:00
Shea Levy 56f2ed0081
Merge pull request #1906 from dtzWill/fix/nix-search
nix search: tests and fix #1893 and part of #1892
2018-03-13 18:43:47 -06:00
Shea Levy aa8bbbf69d
Merge branch 'write-failure-fixes' of git://github.com/lheckemann/nix 2018-03-02 10:59:59 -05:00
Tuomas Tynkkynen a0e38c16bc libexpr: Recognize newline in more places in lexer
Flex's regexes have an annoying feature: the dot matches everything
except a newline. This causes problems for expressions like:

"${0}\
"

where the backslash-newline combination matches this rule instead of the
intended one mentioned in the comment:

    <STRING>\$|\\|\$\\ {
                    /* This can only occur when we reach EOF, otherwise the above
                    (...|\$[^\{\"\\]|\\.|\$\\.)+ would have triggered.
                    This is technically invalid, but we leave the problem to the
                    parser who fails with exact location. */
                    return STR;
                }
However, the parser actually accepts the resulting token sequence
('"' DOLLAR_CURLY 0 '}' STR '"'), which is a problem because the lexer
rule didn't assign anything to yylval. Ultimately this leads to a crash
when dereferencing a NULL pointer in ExprConcatStrings::bindVars().

The fix does change the syntax of the language in some corner cases
but I think it's only turning previously invalid (or crashing) syntax
to valid syntax. E.g.

"a\
b"

and

''a''\
b''

were previously syntax errors but now both result in "a\nb".

Found by afl-fuzz.
2018-03-02 17:30:48 +02:00
Will Dietz c577186f59 tests/search.sh: simplify, don't rely on consistent ordering 2018-03-01 13:25:06 -06:00
Tuomas Tynkkynen 77e9e1ed91 libexpr: Fix prim_replaceStrings() to work on an empty source string
Otherwise, running e.g.

nix-instantiate --eval -E --strict 'builtins.replaceStrings [""] ["X"] "abc"'

would just hang in an infinite loop.

Found by afl-fuzz.

First attempt of this was reverted in e2d71bd186 because it caused
another infinite loop, which is fixed now and a test added.
2018-02-26 19:49:13 +02:00
Will Dietz 8282c60d74 tests: test nix search behavior 2018-02-25 16:40:05 -06:00
Eelco Dolstra de4c03d201
Merge branch 'fix/dry-run-partially' of https://github.com/dtzWill/nix 2018-02-22 12:18:20 +01:00
Eelco Dolstra e2d71bd186
Revert "libexpr: Fix prim_replaceStrings() to work on an empty source string"
This reverts commit 4ea9707591.

It causes an infinite loop in Nixpkgs evaluation,
e.g. "nix-instantiate -A hello" hung.

PR #1886.
2018-02-21 15:35:28 +01:00