The call to nix-env expects a string which represents how old the
derivations are or just "old" which means any generations other than
the current one in use. Currently nix-collect-garbage passes an empty
string to nix-env when using the -d option. This patch corrects the call
to nix-env such that it follows the old behavior.
This hook can be used to set system-specific per-derivation build
settings that don't fit into the derivation model and are too complex or
volatile to be hard-coded into nix. Currently, the pre-build hook can
only add chroot dirs/files through the interface, but it also has full
access to the chroot root.
The specific use case for this is systems where the operating system ABI
is more complex than just the kernel-support system calls. For example,
on OS X there is a set of system-provided frameworks that can reliably
be accessed by any program linked to them, no matter the version the
program is running on. Unfortunately, those frameworks do not
necessarily live in the same locations on each version of OS X, nor do
their dependencies, and thus nix needs to know the specific version of
OS X currently running in order to make those frameworks available. The
pre-build hook is a perfect mechanism for doing just that.
This hook can be used to set system specific per-derivation build
settings that don't fit into the derivation model and are too complex or
volatile to be hard-coded into nix. Currently, the pre-build hook can
only add chroot dirs/files.
The specific use case for this is systems where the operating system ABI
is more complex than just the kernel-supported system calls. For
example, on OS X there is a set of system-provided frameworks that can
reliably be accessed by any program linked to them, no matter the
version the program is running on. Unfortunately, those frameworks do
not necessarily live in the same locations on each version of OS X, nor
do their dependencies, and thus nix needs to know the specific version
of OS X currently running in order to make those frameworks available.
The pre-build hook is a perfect mechanism for doing just that.
This is because we don't want to do HTTP requests on every evaluation,
even though we can prevent a full redownload via the cached ETag. The
default is one hour.
This was causing NixOS VM tests to fail mysteriously since
5ce50cd99e. Nscd could (sometimes) no
longer read /etc/hosts:
open("/etc/hosts", O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
Probably there was some wacky interaction between the guest kernel and
the 9pfs implementation in QEMU.
This function downloads and unpacks the given URL at evaluation
time. This is primarily intended to make it easier to deal with Nix
expressions that have external dependencies. For instance, to fetch
Nixpkgs 14.12:
with import (fetchTarball https://github.com/NixOS/nixpkgs-channels/archive/nixos-14.12.tar.gz) {};
Or to fetch a specific revision:
with import (fetchTarball 2766a4b44e.tar.gz) {};
This patch also adds a ‘fetchurl’ builtin that downloads but doesn't
unpack its argument. Not sure if it's useful though.
Thus, for example, to get /bin/sh in a chroot, you only need to
specify /bin/sh=${pkgs.bash}/bin/sh in build-chroot-dirs. The
dependencies of sh will be added automatically.
This doesn't work anymore if the "strict" chroot mode is
enabled. Instead, add Nix's store path as a dependency. This ensures
that its closure is present in the chroot.
I'm seeing hangs in Glibc's setxid_mark_thread() again. This is
probably because the use of an intermediate process to make clone()
safe from a multi-threaded program (see
524f89f139) is defeated by the use of
vfork(), since the intermediate process will have a copy of Glibc's
threading data structures due to the vfork(). So use a regular fork()
again.
If ‘build-use-chroot’ is set to ‘true’, fixed-output derivations are
now also chrooted. However, unlike normal derivations, they don't get
a private network namespace, so they can still access the
network. Also, the use of the ‘__noChroot’ derivation attribute is
no longer allowed.
Setting ‘build-use-chroot’ to ‘relaxed’ gives the old behaviour.
If ‘--option restrict-eval true’ is given, the evaluator will throw an
exception if an attempt is made to access any file outside of the Nix
search path. This is primarily intended for Hydra, where we don't want
people doing ‘builtins.readFile ~/.ssh/id_dsa’ or stuff like that.
chroot only changes the process root directory, not the mount namespace root
directory, and it is well-known that any process with chroot capability can
break out of a chroot "jail". By using pivot_root as well, and unmounting the
original mount namespace root directory, breaking out becomes impossible.
Non-root processes typically have no ability to use chroot() anyway, but they
can gain that capability through the use of clone() or unshare(). For security
reasons, these syscalls are limited in functionality when used inside a normal
chroot environment. Using pivot_root() this way does allow those syscalls to be
put to their full use.
Sodium's Ed25519 signatures are much shorter than OpenSSL's RSA
signatures. Public keys are also much shorter, so they're now
specified directly in the nix.conf option ‘binary-cache-public-keys’.
The new command ‘nix-store --generate-binary-cache-key’ generates and
prints a public and secret key.
The DT_UNKNOWN fallback code was getting the type of the wrong path,
causing readDir to report "directory" as the type of every file.
Reported by deepfire on IRC.
I.e., not readable to the nixbld group. This improves purity a bit for
non-chroot builds, because it prevents a builder from enumerating
store paths (i.e. it can only access paths it knows about).
Let's not just improve the error message itself, but also the behaviour
to actually work around the ntfs-3g symlink bug. If the readlink() call
returns a smaller size than the stat() call, this really isn't a problem
even if the symlink target really has changed between the calls.
So if stat() reports the size for the absolute path, it's most likely
that the relative path is smaller and thus it should also work for file
system bugs as mentioned in 93002d69fc58c2b71e2dfad202139230c630c53a.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Tested-by: John Ericson <Ericson2314@Yahoo.com>
A message like "error: reading symbolic link `...' : Success" really is
quite confusing, so let's not indicate "success" but rather point out
the real issue.
We could also limit the check of this to just check for non-negative
values, but this would introduce a race condition between stat() and
readlink() if the link target changes between those two calls, thus
leading to a buffer overflow vulnerability.
Reported by @Ericson2314 on IRC. Happened due to a possible ntfs-3g bug
where a relative symlink returned the absolute path (st_)size in stat()
while readlink() returned the relative size.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Tested-by: John Ericson <Ericson2314@Yahoo.com>
In low memory environments, "nix-env -qa" failed because the fork to
run the pager hit the kernel's overcommit limits. Using posix_spawn
gets around this. (Actually, you have to use posix_spawn with the
undocumented POSIX_SPAWN_USEVFORK flag, otherwise it just uses
fork/exec...)
Code that links to libnixexpr (e.g. plugins loaded with importNative, or
nix-exec) may want to provide custom value types and operations on
values of those types. For example, nix-exec is currently using sets
where a custom IO value type would be more appropriate. This commit
provides a generic hook for such types in the form of tExternal and the
ExternalBase virtual class, which contains all functions necessary for
libnixexpr's type-polymorphic functions (e.g. `showType`) to be
implemented.
The function ‘builtins.match’ takes a POSIX extended regular
expression and an arbitrary string. It returns ‘null’ if the string
does not match the regular expression. Otherwise, it returns a list
containing substring matches corresponding to parenthesis groups in
the regex. The regex must match the entire string (i.e. there is an
implied "^<pat>$" around the regex). For example:
match "foo" "foobar" => null
match "foo" "foo" => []
match "f(o+)(.*)" "foooobar" => ["oooo" "bar"]
match "(.*/)?([^/]*)" "/dir/file.nix" => ["/dir/" "file.nix"]
match "(.*/)?([^/]*)" "file.nix" => [null "file.nix"]
The following example finds all regular files with extension .nix or
.patch underneath the current directory:
let
findFiles = pat: dir: concatLists (mapAttrsToList (name: type:
if type == "directory" then
findFiles pat (dir + "/" + name)
else if type == "regular" && match pat name != null then
[(dir + "/" + name)]
else []) (readDir dir));
in findFiles ".*\\.(nix|patch)" (toString ./.)
Before this there was a bug where a `find` was being called on a
not-yet-sorted set. The code was just a mess before anyway, so I cleaned
it up while fixing it.
Especially in WAL mode on a highly loaded machine, this is not a good
idea because it results in a WAL file of approximately the same size
ad the database, which apparently cannot be deleted while anybody is
accessing it.
This was preventing destructors from running. In particular, it was
preventing the deletion of the temproot file for each worker
process. It may also have been responsible for the excessive WAL
growth on Hydra (due to the SQLite database not being closed
properly).
Apparently broken by accident in
8e9140cfde.
With this, attribute sets with a `__functor` attribute can be applied
just like normal functions. This can be used to attach arbitrary
metadata to a function without callers needing to treat it specially.
In particular, gcc 4.6's std::exception::~exception has an exception
specification in c++0x mode, which requires us to use that deprecated
feature in nix (and led to breakage after some recent changes that were
valid c++11).
nix already uses several c++11 features and gcc 4.7 has been around for
over 2 years.
Clearing v.app.right was not enough, because the length field of a
list only takes 32 bits, so the most significant 32 bits of v.app.left
(a.k.a. v.thunk.env) would remain. This could cause Boehm GC to
interpret it as a valid pointer.
This change reduces maximum RSS for evaluating the ‘tested’ job in
nixos/release-small.nix from 1.33 GiB to 0.80 GiB, and runtime by
about 8%.
For the "stdenv accidentally referring to bootstrap-tools", it seems
easier to specify the path that we don't want to depend on, e.g.
disallowedRequisites = [ bootstrapTools ];
It turns out that using clone() to start a child process is unsafe in
a multithreaded program. It can cause the initialisation of a build
child process to hang in setgroups(), as seen several times in the
build farm:
The reason is that Glibc thinks that the other threads of the parent
exist in the child, so in setxid_mark_thread() it tries to get a futex
that has been acquired by another thread just before the clone(). With
fork(), Glibc runs pthread_atfork() handlers that take care of this
(in particular, __reclaim_stacks()). But clone() doesn't do that.
Fortunately, we can use fork()+unshare() instead of clone() to set up
private namespaces.
See also https://www.mail-archive.com/lxc-devel@lists.linuxcontainers.org/msg03434.html.
The Nixpkgs stdenv prints some custom escape sequences to denote
nesting and stuff like that. Most terminals (e.g. xterm, konsole)
ignore them, but some do not (e.g. xfce4-terminal). So for the benefit
of the latter, filter them out.
If a root is a regular file, then its name must denote a store
path. For instance, the existence of the file
/nix/var/nix/gcroots/per-user/eelco/hydra-roots/wzc3cy1wwwd6d0dgxpa77ijr1yp50s6v-libxml2-2.7.7
would cause
/nix/store/wzc3cy1wwwd6d0dgxpa77ijr1yp50s6v-libxml2-2.7.7
to be a root.
This is useful because it involves less I/O (no need for a readlink()
call) and takes up less disk space (the symlink target typically takes
up a full disk block, while directory entries are packed more
efficiently). This is particularly important for hydra.nixos.org,
which has hundreds of thousands of roots, and where reading the roots
can take 25 minutes.
Other operations cannot hang indefinitely (except when we're reading
from stdin, in which case we'll notice a client disconnect). But
monitoring works badly during compressed imports, since there the
client can close the connection before we've sent an ack.
http://hydra.nixos.org/build/12711638
Signal handlers are process-wide, so sending SIGINT to the monitor
thread will cause the normal SIGINT handler to run. This sets the
isInterrupted flag, which is not what we want. So use pthread_cancel
instead.
This is necessary because build-remote.pl now builds via ‘nix-store
--serve’. So if a build hangs without writing to stdout/stderr, and
the client disconnects, then we need to detect that.
The thread calls poll() to wait until a HUP (or other error event)
happens on the client connection. If so, it sends SIGINT to the main
thread, which is then cleaned up normally. This is much nicer than
messing around with SIGPOLL.
‘trusted-users’ is a list of users and groups that have elevated
rights, such as the ability to specify binary caches. It defaults to
‘root’. A typical value would be ‘@wheel’ to specify all users in the
wheel group.
‘allowed-users’ is a list of users and groups that are allowed to
connect to the daemon. It defaults to ‘*’. A typical value would be
‘@users’ to specify the ‘users’ group.
When running NixOps under Mac OS X, we need to be able to import store
paths built on Linux into the local Nix store. However, HFS+ is
usually case-insensitive, so if there are directories with file names
that differ only in case, then importing will fail.
The solution is to add a suffix ("~nix~case~hack~<integer>") to
colliding files. For instance, if we have a directory containing
xt_CONNMARK.h and xt_connmark.h, then the latter will be renamed to
"xt_connmark.h~nix~case~hack~1". If a store path is dumped as a NAR,
the suffixes are removed. Thus, importing and exporting via a
case-insensitive Nix store is round-tripping. So when NixOps calls
nix-copy-closure to copy the path to a Linux machine, you get the
original file names back.
Closes#119.
This makes things more efficient (we don't need to use an SSH master
connection, and we only start a single remote process) and gets rid of
locking issues (the remote nix-store process will keep inputs and
outputs locked as long as they're needed).
It also makes it more or less secure to connect directly to the root
account on the build machine, using a forced command
(e.g. ‘command="nix-store --serve --write"’). This bypasses the Nix
daemon and is therefore more efficient.
Also, don't call nix-store to import the output paths.
There is a long-standing race condition when copying a closure to a
remote machine, particularly affecting build-remote.pl: the client
first asks the remote machine which paths it already has, then copies
over the missing paths. If the garbage collector kicks in on the
remote machine between the first and second step, the already-present
paths may be deleted. The missing paths may then refer to deleted
paths, causing nix-copy-closure to fail. The client now performs both
steps using a single remote Nix call (using ‘nix-store --serve’),
locking all paths in the closure while querying.
I changed the --serve protocol a bit (getting rid of QueryCommand), so
this breaks the SSH substituter from older versions. But it was marked
experimental anyway.
Fixes#141.
This can be used to import a dynamic shared object and return an
arbitrary value, including new primops. This can be used both to test
new primops without having to recompile nix every time, and to build
specialized primops that probably don't belong upstream (e.g. a function
that calls out to gpg to decrypt a nixops secret as-needed).
The imported function should initialize the Value & as needed. A single
import can define multiple values by creating an attrset or list, of
course.
An example initialization function might look like:
extern "C" void initialize(nix::EvalState & state, nix::Value & v)
{
v.type = nix::tPrimOp;
v.primOp = NEW nix::PrimOp(myFun, 1, state.symbols.create("myFun"));
}
Then `builtins.importNative ./example.so "initialize"` will evaluate to
the primop defined in the myFun function.
When copying a large path causes the daemon to run out of memory, you
now get:
error: Nix daemon out of memory
instead of:
error: writing to file: Broken pipe
It's slower than ExprVar since it doesn't compute a static
displacement. Since we're not using the throw primop in the
implementation of <...> anymore, it's also not really needed.
Nix search path lookups like <nixpkgs> are now desugared to ‘findFile
nixPath <nixpkgs>’, where ‘findFile’ is a new primop. Thus you can
override the search path simply by saying
let
nixPath = [ { prefix = "nixpkgs"; path = "/my-nixpkgs"; } ];
in ... <nixpkgs> ...
In conjunction with ‘scopedImport’ (commit
c273c15cb1), the Nix search path can be
propagated across imports, e.g.
let
overrides = {
nixPath = [ ... ] ++ builtins.nixPath;
import = fn: scopedImport overrides fn;
scopedImport = attrs: fn: scopedImport (overrides // attrs) fn;
builtins = builtins // overrides;
};
in scopedImport overrides ./nixos
‘scopedImport’ works like ‘import’, except that it takes a set of
attributes to be added to the lexical scope of the expression,
essentially extending or overriding the builtin variables. For
instance, the expression
scopedImport { x = 1; } ./foo.nix
where foo.nix contains ‘x’, will evaluate to 1.
This has a few applications:
* It allows getting rid of function argument specifications in package
expressions. For instance, a package expression like:
{ stdenv, fetchurl, libfoo }:
stdenv.mkDerivation { ... buildInputs = [ libfoo ]; }
can now we written as just
stdenv.mkDerivation { ... buildInputs = [ libfoo ]; }
and imported in all-packages.nix as:
bar = scopedImport pkgs ./bar.nix;
So whereas we once had dependencies listed in three places
(buildInputs, the function, and the call site), they now only need
to appear in one place.
* It allows overriding builtin functions. For instance, to trace all
calls to ‘map’:
let
overrides = {
map = f: xs: builtins.trace "map called!" (map f xs);
# Ensure that our override gets propagated by calls to
# import/scopedImport.
import = fn: scopedImport overrides fn;
scopedImport = attrs: fn: scopedImport (overrides // attrs) fn;
# Also update ‘builtins’.
builtins = builtins // overrides;
};
in scopedImport overrides ./bla.nix
* Similarly, it allows extending the set of builtin functions. For
instance, during Nixpkgs/NixOS evaluation, the Nixpkgs library
functions could be added to the default scope.
There is a downside: calls to scopedImport are not memoized, unlike
import. So importing a file multiple times leads to multiple parsings
/ evaluations. It would be possible to construct the AST only once,
but that would require careful handling of variables/environments.
If a build log is not available locally, then ‘nix-store -l’ will now
try to download it from the servers listed in the ‘log-servers’ option
in nix.conf. For instance, if you have:
log-servers = http://hydra.nixos.org/log
then it will try to get logs from http://hydra.nixos.org/log/<base
name of the store path>. So you can do things like:
$ nix-store -l $(which xterm)
and get a log even if xterm wasn't built locally.
By preloading all inodes in the /nix/store/.links directory, we can
quickly determine of a hardlinked file was already linked to the hashed
links.
This is tolerant of removing the .links directory, it will simply
recalculate all hashes in the store.
If an inode in the Nix store has more than 1 link, it probably means that it was linked into .links/ by us. If so, skip.
There's a possibility that something else hardlinked the file, so it would be nice to be able to override this.
Also, by looking at the number of hardlinks for each of the files in .links/, you can get deduplication numbers and space savings.
The option '--delete-generations Nd' deletes all generations older than N
days. However, most likely the user does not want to delete the
generation that was active N days ago.
For example, say that you have these 3 generations:
1: <30 days ago>
2: <15 days ago>
3: <1 hour ago>
If you do --delete-generations 7d (say, as part of a cron job), most
likely you still want to keep generation 2, i.e. the generation that was
active 7 days ago (and for most of the past 7 days, in fact).
This patch fixes this issue. Note that this also affects
'nix-collect-garbage --delete-older-than Nd'.
Thanks to @roconnor for noticing the issue!
This allows error messages like:
error: the anonymous function at `/etc/nixos/configuration.nix:1:1'
called without required argument `foo', at
`/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/lib/modules.nix:77:59'
While running Python 3’s test suite, we noticed that on some systems
/dev/pts/ptmx is created with permissions 0 (that’s the case with my
Nixpkgs-originating 3.0.43 kernel, but someone with a Debian-originating
3.10-3 reported not having this problem.)
There’s still the problem that people without
CONFIG_DEVPTS_MULTIPLE_INSTANCES=y are screwed (as noted in build.cc),
but I don’t see how we could work around it.
Since the addition of build-max-log-size, a call to
handleChildOutput() can result in cancellation of a goal. This
invalidated the "j" iterator in the waitForInput() loop, even though
it was still used afterwards. Likewise for the maxSilentTime
handling.
Probably fixes#231. At least it gets rid of the valgrind warnings.
Ludo reported this error:
unexpected Nix daemon error: boost::too_few_args: format-string refered to more arguments than were passed
coming from this line:
printMsg(lvlError, run.program + ": " + string(err, 0, p));
The problem here is that the string ends up implicitly converted to a
Boost format() object, so % characters are treated specially. I
always assumed (wrongly) that strings are converted to a format object
that outputs the string as-is.
Since this assumption appears in several places that may be hard to
grep for, I've added some C++ type hackery to ensures that the right
thing happens. So you don't have to worry about % in statements like
printMsg(lvlError, "foo: " + s);
or
throw Error("foo: " + s);
The daemon now creates /dev deterministically (thanks!). However, it
expects /dev/kvm to be present.
The patch below restricts that requirement (1) to Linux-based systems,
and (2) to systems where /dev/kvm already exists.
I’m not sure about the way to handle (2). We could special-case
/dev/kvm and create it (instead of bind-mounting it) in the chroot, so
it’s always available; however, it wouldn’t help much since most likely,
if /dev/kvm missing, then KVM support is missing.
Currently, clients cannot recover from an isValidPath RPC with an
invalid path parameter because the daemon closes the connection when
that happens.
More precisely:
1. in performOp, wopIsValidPath case, ‘readStorePath’ raises an
‘Error’ exception;
2. that exception is caught by the handler in ‘processConnection’;
3. the handler determines errorAllowed == false, and thus exits after
sending the message.
This last part is fixed by calling ‘startWork’ early on, as in the patch
below.
The same reasoning could be applied to all the RPCs that take one or
more store paths as inputs, but isValidPath is, by definition, likely to
be passed invalid paths in the first place, so it’s important for this
one to allow recovery.
Since the meta attributes were not sorted, attribute lookup could
fail, leading to package priorities and active flags not working
correctly.
Broken since 0f24400d90.
If we're evaluating some application ‘v = f x’, we can't store ‘f’
temporarily in ‘v’, because if ‘f x’ refers to ‘v’, it will get ‘f’
rather than an infinite recursion error.
Unfortunately, this breaks the tail call optimisation introduced in
c897bac549.
Fixes#217.
We were relying on SubstitutionGoal's destructor releasing the lock,
but if a goal is a top-level goal, the destructor won't run in a
timely manner since its reference count won't drop to zero. So
release it explicitly.
Fixes#178.
Fixes#121. Note that we don't warn about missing $NIX_PATH entries
because it's intended that some may be missing (cf. the default
$NIX_PATH on NixOS, which includes paths like /etc/nixos/nixpkgs for
backward compatibility).
The flag ‘--check’ to ‘nix-store -r’ or ‘nix-build’ will cause Nix to
redo the build of a derivation whose output paths are already valid.
If the new output differs from the original output, an error is
printed. This makes it easier to test if a build is deterministic.
(Obviously this cannot catch all sources of non-determinism, but it
catches the most common one, namely the current time.)
For example:
$ nix-build '<nixpkgs>' -A patchelf
...
$ nix-build '<nixpkgs>' -A patchelf --check
error: derivation `/nix/store/1ipvxsdnbhl1rw6siz6x92s7sc8nwkkb-patchelf-0.6' may not be deterministic: hash mismatch in output `/nix/store/4pc1dmw5xkwmc6q3gdc9i5nbjl4dkjpp-patchelf-0.6.drv'
The --check build fails if not all outputs are valid. Thus the first
call to nix-build is necessary to ensure that all outputs are valid.
The current outputs are left untouched: the new outputs are either put
in a chroot or diverted to a different location in the store using
hash rewriting.
This substituter connects to a remote host, runs nix-store --serve
there, and then forwards substituter commands on to the remote host and
sends their results to the calling program. The ssh-substituter-hosts
option can be specified as a list of hosts to try.
This is an initial implementation and, while it works, it has some
limitations:
* Only the first host is used
* There is no caching of query results (all queries are sent to the
remote machine)
* There is no informative output (such as progress bars)
* Some failure modes may cause unhelpful error messages
* There is no concept of trusted-ssh-substituter-hosts
Signed-off-by: Shea Levy <shea@shealevy.com>
nix-store --export takes a tmproot, which can only release by exiting.
Substituters don't currently work in a way that could take advantage of
the looping, anyway.
Signed-off-by: Shea Levy <shea@shealevy.com>
This is essentially the substituter API operating on the local store,
which will be used by the ssh substituter. It runs in a loop rather than
just taking one command so that in the future nix will be able to keep
one connection open for multiple instances of the substituter.
Signed-off-by: Shea Levy <shea@shealevy.com>
This allows running nix-instantiate --eval-only without performing the
evaluation in readonly mode, letting features like import from
derivation and automatic substitution of builtins.storePath paths work.
Signed-off-by: Shea Levy <shea@shealevy.com>
Namely:
nix-store: derivations.cc:242: nix::Hash nix::hashDerivationModulo(nix::StoreAPI&, nix::Derivation): Assertion `store.isValidPath(i->first)' failed.
This happened because of the derivation output correctness check being
applied before the references of a derivation are valid.
Now, in addition to a."${b}".c, you can write a.${b}.c (applicable
wherever dynamic attributes are valid).
Signed-off-by: Shea Levy <shea@shealevy.com>
*headdesk*
*headdesk*
*headdesk*
So since commit 22144afa8d, Nix hasn't
actually checked whether the content of a downloaded NAR matches the
hash specified in the manifest / NAR info file. Urghhh...
This doesn't change any functionality but moves some behavior out of the
parser and into the evaluator in order to simplify the code.
Signed-off-by: Shea Levy <shea@shealevy.com>
Since addAttr has to iterate through the AttrPath we pass it, it makes
more sense to just iterate through the AttrNames in addAttr instead. As
an added bonus, this allows attrsets where two dynamic attribute paths
have the same static leading part (see added test case for an example
that failed previously).
Signed-off-by: Shea Levy <shea@shealevy.com>
This adds new syntax for attribute names:
* attrs."${name}" => getAttr name attrs
* attrs ? "${name}" => isAttrs attrs && hasAttr attrs name
* attrs."${name}" or def => if attrs ? "${name}" then attrs."${name}" else def
* { "${name}" = value; } => listToAttrs [{ inherit name value; }]
Of course, it's a bit more complicated than that. The attribute chains
can be arbitrarily long and contain combinations of static and dynamic
parts (e.g. attrs."${foo}".bar."${baz}" or qux), which is relatively
straightforward for the getAttrs/hasAttrs cases but is more complex for
the listToAttrs case due to rules about duplicate attribute definitions.
For attribute sets with dynamic attribute names, duplicate static
attributes are detected at parse time while duplicate dynamic attributes
are detected when the attribute set is forced. So, for example, { a =
null; a.b = null; "${"c"}" = true; } will be a parse-time error, while
{ a = {}; "${"a"}".b = null; c = true; } will be an eval-time error
(technically that case could theoretically be detected at parse time,
but the general case would require full evaluation). Moreover, duplicate
dynamic attributes are not allowed even in cases where they would be
with static attributes ({ a.b.d = true; a.b.c = false; } is legal, but {
a."${"b"}".d = true; a."${"b"}".c = false; } is not). This restriction
might be relaxed in the future in cases where the static variant would
not be an error, but it is not obvious that that is desirable.
Finally, recursive attribute sets with dynamic attributes have the
static attributes in scope but not the dynamic ones. So rec { a = true;
"${"b"}" = a; } is equivalent to { a = true; b = true; } but rec {
"${"a"}" = true; b = a; } would be an error or use a from the
surrounding scope if it exists.
Note that the getAttr, getAttr or default, and hasAttr are all
implemented purely in the parser as syntactic sugar, while attribute
sets with dynamic attribute names required changes to the AST to be
implemented cleanly.
This is an alternative solution to and closes#167
Signed-off-by: Shea Levy <shea@shealevy.com>
Certain desugaring schemes may require the parser to use some builtin
function to do some of the work (e.g. currently `throw` is used to
lazily cause an error if a `<>`-style path is not in the search path)
Unfortunately, these names are not reserved keywords, so an expression
that uses such a syntactic sugar will not see the expected behavior
(see tests/lang/eval-okay-redefine-builtin.nix for an example).
This adds the ExprBuiltin AST type, which when evaluated uses the value
from the rootmost variable scope (which of course is initialized
internally and can't shadow any of the builtins).
Signed-off-by: Shea Levy <shea@shealevy.com>
This will allow e.g. channel expressions to use builtins.storePath IFF
it is safe to do so without knowing if the path is valid yet.
Signed-off-by: Shea Levy <shea@shealevy.com>
