This has been causing various seemingly spurious CI failures as well as
some failures on people running tests on beta builds.
lix> ++(nix-collect-garbage-dry-run.sh:20) nix-store --gc --print-dead
lix> ++(nix-collect-garbage-dry-run.sh:20) wc -l
lix> finding garbage collector roots...
lix> error: Listing pid 87261 file descriptors: Undefined error: 0
There is no real way to write a proper test for this, other than to
start a process like the following:
int main(void) {
for (int i = 0; i < 1000; ++i) {
close(i);
}
sleep(10000);
}
and then let Lix's gc look at it.
I have a relatively high confidence this *will* fix the problem since I
have manually confirmed the behaviour of the libproc call is
as-unexpected, and it would perfectly explain the observed symptom.
Fixes: lix-project/lix#446
Change-Id: I67669b98377af17895644b3bafdf42fc33abd076
* changes:
tree-wide: fix various lint warnings
flake & doxygen: update tagline
nix flake metadata: print modified dates for input flakes
cli: eat terminal codes from stdout also
Implement forcing CLI colour on, and document it better
manual: fix a syntax error in redirects.js that made it not do anything
misc docs/meson tidying
build: implement clang-tidy using our plugin
The growth of the seccomp filter in 127ee1a101
made its compilation time significant (roughly 10 milliseconds have been
measured on one machine). For this reason, it is now precompiled and cached in
the parent process so that this overhead is not hit for every single build. It
is still not optimal when going through the daemon, because compilation still
happens once per client, but it's better than before and doing it only once for
the entire daemon requires excessive crimes with the current architecture.
Fixes: lix-project/lix#461
Change-Id: I2277eaaf6bab9bd74bbbfd9861e52392a54b61a3
This is a preparation for precompiling the filter, which is done separately.
The behaviour should be unchanged for now.
Change-Id: I899aa7242962615949208597aca88913feba1cb8
The seccomp setup code was a huge chunk of conditionally compiled
platform-specific code. For this reason, it is appropriate to move it to the
platform-specific implementation file. Ideally its setup could be moved a bit
to make it happen at the same place as the Darwin restrictions, but that change
is going to be less mechanical.
Change-Id: I496aa3c4fabf34656aba1e32b0089044ab5b99f8
This was always in the lock file and we can simply actually print it.
The test for this is a little bit silly but it should correctly
control for my daring to exercise timezone code *and* locale code in a
test, which I strongly suspect nobody dared do before.
Sample (abridged):
```
Path: /nix/store/gaxb42z68bcr8lch467shvmnhjjzgd8b-source
Last modified: 1970-01-01 00:16:40
Inputs:
├───flake-compat: github:edolstra/flake-compat/0f9255e01c2351cc7d116c072cb317785dd33b33
│ Last modified: 2023-10-04 13:37:54
├───flake-utils: github:numtide/flake-utils/b1d9ab70662946ef0850d488da1c9019f3a9752a
│ Last modified: 2024-03-11 08:33:50
│ └───systems: github:nix-systems/default/da67096a3b9bf56a91d16901293e51ba5b49a27e
│ Last modified: 2023-04-09 08:27:08
```
Change-Id: I355f82cb4b633974295375ebad646fb6e2107f9b
This *should* be sound, plus or minus the amount that the terminal code
eating code is messed up already.
This is useful for testing CLI output because it will strip the escapes
enough to just shove the expected output in a file.
Change-Id: I8a9b58fafb918466ac76e9ab585fc32fb9294819
The docs page has an incorrect escape that leads to a backslash
appearing in output. Meson stuff is self-explanatory, just shortens and
simplifies a bit.
Change-Id: Ib63adf934efd3caeb82ca82988f230e8858a79f9
Expose an option for disabling the BDW-GC build dependency entirely. Fix the
place where one of its headers was included (unnecessarily) without proper
guarding. Finally, use this machinery to exclude BDW-GC from the ASAN builds
entirely (its usage has already been disabled due to compatibility issues
anyway), to ensure this configuration is not regressed again.
Change-Id: I2ebe8094abf67e7d1e99eed971de3e99d071c10b
this begins a long and arduous journey to remove all result state from
Goal, to eventually drop the std::enable_shared_from_this base, and to
completely eliminate all unsynchronized modification of states of both
Goal and Worker. by the end of this we will hopefully be able to start
and reap multiple derivation builds in parallel, which should speed up
the process quite a bit (at least for short local builds, others might
not notice a large difference. the build hooks will remain a problem.)
Change-Id: I57dcd9b2cab4636ed4aa24cdec67124fef883345
In the SSH code, the logger was conditionally paused, but unconditionally
resumed. This was fine as long as resuming the logger was idempotent. Starting
with 0dd1d8ca1c, it isn't any more, and the
behaviour of the code in question was missed. Consequently, an assertion
failure is triggered for example when performing builds against an "SSH" store
on localhost. Fix the issue by only resuming the logger when it has actually
been paused.
Fixes: lix-project/lix#458
Change-Id: Ib1e4d047744a129f15730b7216f9c9368c2f4211
we still mutate goal state to store the results of any given goal run,
but now we also have that information in Worker and could in theory do
something else with it. we could return a map of goal to goal results,
which would also let us better diagnose failures of subgoals (at all).
Change-Id: I1df956bbd9fa8cc9485fb6df32918d68dda3ff48
this is the first step towards removing all result-related mutation of
Goal state from goal implementations themselves, and into Worker state
instead. once that is done we can treat all non-const Goal fields like
private state of the goal itself, and make threading of goals possible
Change-Id: I69ff7d02a6fd91a65887c6640bfc4f5fb785b45c
once goals run on multiple threads these fields must by synchronized as
one, or we try to run build hooks to often (or worse, not often enough)
Change-Id: I47860e46fe5c6db41755b2a3a1d9dbb5701c4ca4
this will usually be used either directly (which is always fine) or in
Finally blocks (where it must never throw execptions). make sure that,
exceptions being handled or not, the calling wait() in Finally doesn't
cause crashes due to the Finally no-nested-exceptions-thrown assertion
Change-Id: Ib83a5d9483b1fe83b9a957dcefeefce5d088f06d
The original attempt at this introduced a regression; this commit
reverts the revert and fixes the regression.
This reverts commit 3e151d4d77.
Fix to the regression:
flakeref: fix handling of `?dir=` param for flakes in subdirs
As reported in #419[1], accessing a flake in a subdir of a Git
repository fails with the previous commit[2] applied with the error
error: unsupported Git input attribute 'dir'
The problem is that the `dir`-param is inserted into the parsed URL if a
flake is fetched from the subdir of a Git repository. However, for the
fetching part this isn't even needed. The fix is to just pass `subdir`
as second argument to `FlakeRef` (which needs a `basedir` that can be
empty) and leave the parsedURL as-is.
Added a regression test to make sure we don't run into this again.
[1] lix-project/lix#419
[2] e22172aaf6b6a366cecd3c025590e68fa2b91bcc,
originally 3e151d4d77
Change-Id: I2c72d5a32e406a7ca308e271730bd0af01c5d18b
* changes:
remove unused headers in installable-attr-path
libexpr: include the type of the non-derivation value in the type error
libexpr: mild cleanup to getDerivations
libexpr: DrvInfo: remove unused bad-citizen constructor
cleanup and slightly refactor DrvInfo::queryOutputs
* changes:
releng: move officialRelease to version.json
Add -Werror CI job
ci: add a asan+ubsan test run on x86_64-linux
tree-wide: add support for asan!
Shuffled the logic around a bit so the shorter code paths are early
returns, added comments, etc.
Should be NFC.
Change-Id: Ie3ddb3d0eddd614d6f8c37bf9a4d5a50282084ea
DrvInfo's constructor that only takes `EvalState` leaves everything else
empty; a DrvInfo which has no iota of information about the derivation
it represents is not useful, and was not used anywhere.
Change-Id: Ic4d93a08cb2748b8cef9a61e41e70404834b23f9
What if you could find memory bugs in Lix without really trying very
hard? I've had variously scuffed patches to do this, but this is
blocked on boost coroutines removal at this point tbh.
Change-Id: Id762af076aa06ad51e77a6c17ed10275929ed578
there are no other uses for this yet, but asking for just a subset of
outputs does seem at least somewhat useful to have as a generic thing
Change-Id: I30ff5055a666c351b1b086b8d05b9d7c9fb1c77a
If `:edit`ing a store path, don't reload repl afterwards
to avoid losing local variables: store is immutable,
so "editing" a store path is always just viewing it.
Resolves: lix-project/lix#341
Change-Id: I3747f75ce26e0595e953069c39ddc3ee80699718
limiting CA substitutions was a rather recent addition, and it used a
dedicated counter to not interfere with regular substitutions. though
this works fine it somewhat contradicts the documentation; job limits
should apply to all kinds of substitutions, or be one limit for each.
Change-Id: I1505105b14260ecc1784039b2cc4b7afcf9115c8
all goals do this. it makes no sense to not notify a goal of EOF
conditions because this is the universal signal for "child done"
Change-Id: Ic3980de312547e616739c57c6248a8e81308b5ee
just update progress every time a goal has returned from work(). there
seem to be no performance penalties, and the code is much simpler now.
Change-Id: I288ee568b764ee61f40a498d986afda49987cb50
bindPath/doBind is a useful function in build that is used in several
parts of LocalDerivationGoal. Moving this function makes it easier to
split LocalDerivationGoal implementation between several files.
Change-Id: Ic5a0768479c153c1aa3ed425f12604b20bbf0f42
Unfortunately, io_uring is totally opaque to seccomp, and while currently there
are no dangerous operations implemented, there is no guarantee that it remains
this way. This means that io_uring should be blocked entirely to ensure that
the sandbox is future-proof. This has not been observed to cause issues in
practice.
Change-Id: I45d3895f95abe1bc103a63969f444c334dbbf50d
Previously, system call filtering (to prevent builders from storing files with
setuid/setgid permission bits or extended attributes) was performed using a
blocklist. While this looks simple at first, it actually carries significant
security and maintainability risks: after all, the kernel may add new syscalls
to achieve the same functionality one is trying to block, and it can even be
hard to actually add the syscall to the blocklist when building against a C
library that doesn't know about it yet. For a recent demonstration of this
happening in practice to Nix, see the introduction of fchmodat2 [0] [1].
The allowlist approach does not share the same drawback. While it does require
a rather large list of harmless syscalls to be maintained in the codebase,
failing to update this list (and roll out the update to all users) in time has
rather benign effects; at worst, very recent programs that already rely on new
syscalls will fail with an error the same way they would on a slightly older
kernel that doesn't support them yet. Most importantly, no unintended new ways
of performing dangerous operations will be silently allowed.
Another possible drawback is reduced system call performance due to the larger
filter created by the allowlist requiring more computation [2]. However, this
issue has not convincingly been demonstrated yet in practice, for example in
systemd or various browsers. To the contrary, it has been measured that the the
actual filter constructed here has approximately the same overhead as a very
simple filter blocking only one system call.
This commit tries to keep the behavior as close to unchanged as possible. The
system call list is in line with libseccomp 2.5.5 and glibc 2.39, which are the
latest versions at the point of writing. Since libseccomp 2.5.5 is already a
requirement and the distributions shipping this together with older versions of
glibc are mostly not a thing any more, this should not lead to more build
failures any more.
[0] https://github.com/NixOS/nixpkgs/issues/300635
[1] https://github.com/NixOS/nix/issues/10424
[2] https://github.com/flatpak/flatpak/pull/4462#issuecomment-1061690607
Change-Id: I541be3ea9b249bcceddfed6a5a13ac10b11e16ad
In f047e4357b, I missed the behavior that if
building without a dedicated build user (i.e. in single-user setups), seccomp
setup failures are silently ignored. This was introduced without explanation 7
years ago (ff6becafa8). Hopefully the only
use-case nowadays is causing spurious test suite successes when messing up the
seccomp filter during development. Let's try removing it.
Change-Id: Ibe51416d9c7a6dd635c2282990224861adf1ceab
getSelfExe is used in a few places re-execute nix.
Current code in this file uses ifdefs to support several
platforms, just keep doing that
Change-Id: Iecc2ada0101aea0c30524e3a1218594f919d74bf
This was done originally because std::smatch does not accept `const char
*` as iterators. However, this was because we should have been using
std::cmatch instead.
Change-Id: Ibe73851fd39755e883df2d33d22fed72ac0a04ae
Nobody has stepped up to add further support for Hurd since this code
appeared in 2010 or 2014. We don't need it.
Change-Id: I400b2031a225551ea3c71a3ef3ea9fdb599dfba3
Use libprocstat to find garbage collector roots on FreeBSD.
Tested working on a FreeBSD machine, although there is no CI yet
Change-Id: Id36bac8c3de6cc4de94e2d76e9663dd4b76068a9
(cherry picked from commit 8cd1d02f90eb9915e640c5d370d919fad9833c65)
nix flake show: Only print up to the first new line if it exists.
(cherry picked from commit 5281a44927bdb51bfe6e5de12262d815c98f6fe7)
add tests
(cherry picked from commit 74ae0fbdc70a5079a527fe143c4832d1357011f7)
Handle long strings, embedded new lines and empty descriptions
(cherry picked from commit 2ca7b3afdbbd983173a17fa0a822cf7623601367)
Account for total length of 80
(cherry picked from commit 1cc808c18cbaaf26aaae42bb1d7f7223f25dd364)
docs: add nix flake show description release note
fix: remove white space
nix flake show: trim length based on terminal size
test: account for terminal size
docs(flake-description): before and after commands; add myself to credits
Upstream-PR: https://github.com/NixOS/nix/pull/10980
Change-Id: Ie1c667dc816b3dd81e65a1f5395e57ea48ee0362
Error is pretty large, and most goals do not fail. this alone more than
halves the size of Goal on x86_64-linux, from 720 bytes down to 344. in
derived classes the difference is not as dramatic, but even the largest
derived class (`LocalDerivationGoal`) loses almost 20% of its footprint
Change-Id: Ifda8f94c81b6566eeb3e52d55d9796ec40c7bce8
the goals are either already using std::async and merely forgot to
remove std::thread vestiges or they emulate async with threads and
promises. we can simply use async directly everywhere for clarity.
Change-Id: I3f05098310a25984f10fff1e68c573329002b500
under owner_less it's equivalent to insert(), only sometimes a little
bit faster because it does not construct a weak_ptr if the goal is in
the set already. this small difference in performance does not matter
here and c++23 will make insert transparent anyway, so we can drop it
Change-Id: I7cbd7d6e0daa95d67145ec58183162f6c4743b15
*accidentally* overriding a function is almost guaranteed to be an
error. overriding a function without labeling it as such is merely
bad style, but bad style that makes the code harder to understand.
Change-Id: Ic0594f3d1604ab6b3c1a75cb5facc246effe45f0
Commit 0109368c3f missed to include a required
header, which is not noticed when the precompiled header is enabled because
it's included in that. Also include it in the file so that the build without
precompiled header works too.
Change-Id: Id7a7979684b64f937f7f8191612952d73c113015
Due to a leftover from a previous version where the buffer was allocated on the
stack, the change introduced in commit 4ec87742a1
accidentally passes the size of a pointer as the size of the buffer to the
decompressor. Since the former is much smaller (usually 8 bytes instead of 64
kilobytes), this is safe, but leads to considerable overhead; most notably, due
to excessive progress reports, which happen for each chunk. Pass the proper
buffer size instead.
Change-Id: If4bf472d33e21587acb5235a2d99e3cb10914633
This commit adds a new helper template function to gc-alloc.hh (which is
probably where you want to look at first, O great reviewer [custom file
ordering in review diffs when]), which uses a type argument to determine
the size to allocate, rather than making the caller use sizeof().
Change-Id: Ib5d138d91a28bdda304a80db24ea9fb08669ad22
The purpose of this function has little to do with immutability. Value's
strings are never mutated, and the point of this function is to
singleton empty strings.
Change-Id: Ifd41dd952409d54e4d3de9ab59064e6928b0e480
SimpleLogger is not fully thread-safe, and all loggers that wrap it are
also not safe accordingly. this does not affect much, but in rare cases
it can cause interleaving of messages on stderr when used with the json
or raw log formats. the fix applied here is a bit of a hack, but fixing
this properly requires rearchitecting the logger infrastructure. nested
loggers are not the most natural abstraction here, and it is biting us.
Change-Id: Ifbf34fe1e85c60e73b59faee50e7411c7b5e7c12
it's only used once, and even that one use is highly questionable. more
instances of warnOnce should be much more principled than this has been
Change-Id: I5856570c99cb44462e700d753d0c706a5db03c4b
If useChroot = false, and user namespaces aren't available for some
reason (e.g. within a Docker container), this fixes a pointless warning
being emitted, as we would never attempt to use them even if they were
available.
Change-Id: Ibcee91c088edd2cd19e70218d5a5802bff8f537b
This removes a *whole load* of variables from scope and enforces thread
boundaries with the type system.
There is not much change of significance in here, so the things to watch
out for while reviewing it are primarily that the destructor ordering
may have changed inadvertently, I think.
Change-Id: I3cd87e6d5a08dfcf368637407251db22a8906316
* changes:
Fixup a bunch of references to nixos.org manuals
Add release notes for removing overflow from Nix language
expr: fix a compiler warning about different signs in comparison
* changes:
doc/release-notes: add for pretty printing improvements
libexpr/print: do not show elided nested items when there are none
libexpr/print: never show empty attrsets or derivations as «repeated»
libexpr/print: pretty-print idempotently
* changes:
docs: document the actual comparison rules instead of lies
daemon: remove workaround for macOS kernel bug that seems fixed
daemon: fix a crash bug "FATAL: exception not rethrown"
When the configured maximum depth has been reached, attribute sets and lists
are printed with ellipsis to indicate the elision of nested items. Previously,
this happened even in case the structure being printed is empty, so that such
items do not in fact exist. This is confusing, so stop doing it.
Change-Id: I0016970dad3e42625e085dc896e6f476b21226c9
The repeated value detection logic exists so that the occurrence of large
common substructures does not fill up the screen or the computer's memory.
However, empty attribute sets and derivations (when their detection is enabled)
are always cheap to print, and in practice I have observed them to make up a
significant majority of the cases where I was annoyed by the repeated value
detection kicking in. Furthermore, `nix-instantiate --eval` already disables
this logic for empty attribute sets, and empty lists are already exempted
everywhere. For these reasons, always print empty attribute sets and
derivations as what they are.
Change-Id: I5dac8e7739f9d726b76fd0521ec46f38af94463f
When pretty-printing is enabled, previously an unforced thunk would trigger
indentation, even when it subsequently does not evaluate to a nested structure.
The resulting output looked inconsistent, and furthermore pretty-printing was
not idempotent (since pretty-printing the same value again, which is now fully
evaluated, will not trigger indentation).
When strict evaluation is enabled, force the item before inspecting its type,
so that it is properly known whether it contains a nested structure.
Furthermore, there is no need to cause indentation for unforced thunks, since
the very next operation will be printing them as `«thunk»`.
This is mostly a port of https://github.com/NixOS/nix/pull/11100 , but we only
force the item when it's going to be forced anyway due to strict
pretty-printing, and a new test was written since the REPL testing framework in
Lix is different.
Co-Authored-By: Robert Hensing <robert@roberthensing.nl>
Change-Id: Ib7560fe531d09e05ca6b2037a523fe21a26d9d58
this is cursed. deeply and profoundly cursed. under NO CIRCUMSTANCES
must protocol serializer helpers be applied to temporaries! doing so
will inevitably cause dangling references and cause the entire thing
to crash. we need to do this even so to get rid of boost coroutines,
and likewise to encapsulate the serializers we suffer today at least
a little bit to allow a gradual migration to an actual IPC protocol.
(this isn't a problem that's unique to generators. c++ coroutines in
general cannot safely take references to arbitrary temporaries since
c++ does not have a lifetime system that can make this safe. -sigh-)
Change-Id: I2921ba451e04d86798752d140885d3c5cc08e146
this doesn't have a test because this code path is only reached by
clients that predate 2.4, and we really should not be caring about
those any more right now. even the test suite doesn't, and the few
tests that might care are disabled because they will not even work
Change-Id: Id9eb190065138fedb2c7d90c328ff9eb9d97385b
this is not completely necessary at this point because the parser right
now already returns a generator to pass through all input data it read,
but the nar parser *was* very lax and would accept nars that weren't in
canonical form (defined as the form dumpPath would return). nar hashing
depends on these things, and as such rewriting the parser now allows us
to reject non-canonical nars that extract to the same store contents as
their canonical counterpart but have different nar hashes despite that.
Change-Id: Iccd319e3bd5912d8297014c84c495edc59019bb7
This was filed as https://github.com/nixos/nix/issues/7584, but as far
as I can tell, the previous solution of POLLHUP works just fine on macOS
14. I've also tested on an ancient machine with macOS 10.15.7, which
also has POLLHUP work correctly.
It's possible this might regress some older versions of macOS that have
a kernel bug, but I went looking through the history on the sources and
didn't find anything that looked terribly convincingly like a bug fix
between 2020 and today. If such a broken version exists, it seems pretty
reasonable to suggest simply updating the OS.
Change-Id: I178a038baa000f927ea2cbc4587d69d8ab786843
This is caused by pthread_cancel effectively throwing a
not-specifically-identifiable C++ exception into the targeted thread,
which, if it is not rethrown, terminates the process entirely.
This is rather "impolite" behaviour, we would say. But thread
cancellation is *always* busted, and we should simply not use it where
unnecessary. It's particularly unnecessary when what we *actually* need
it for is, err, interrupting a poll(2).
That can in turn be achieved by simply listening to more stuff in the
poll, namely, a pipe, which we send a character to when needing to
stop the thread.
While looking at this code, we also investigated whether any of the
poll() madness is required, or was even *ever* required. Curiously we
found in the XNU kernel source code that the thing about needing to
listen to POLLHUP is probably *correct*, but switching it to POLLRDNORM
should not have made any difference at all. We've left a FIXME to look
into that further because what's written here is super janky.
94d3b45284/bsd/kern/sys_generic.c (L1751-L1758)
This is the crash on some Hydra machines:
Thread 1 (Thread 0x7f56b77776c0 (LWP 955542) (Exiting)):
0 0x00007f56b8e9b7dc in __pthread_kill_implementation () from /nix/store/m71p7f0nymb19yn1dascklyya2i96jfw-glibc-2.39-52/lib/libc.so.6
1 0x00007f56b8e49516 in raise () from /nix/store/m71p7f0nymb19yn1dascklyya2i96jfw-glibc-2.39-52/lib/libc.so.6
2 0x00007f56b8e31935 in abort () from /nix/store/m71p7f0nymb19yn1dascklyya2i96jfw-glibc-2.39-52/lib/libc.so.6
3 0x00007f56b8e327f3 in __libc_message_impl.cold () from /nix/store/m71p7f0nymb19yn1dascklyya2i96jfw-glibc-2.39-52/lib/libc.so.6
4 0x00007f56b8e8e8e9 in __libc_fatal () from /nix/store/m71p7f0nymb19yn1dascklyya2i96jfw-glibc-2.39-52/lib/libc.so.6
5 0x00007f56b8ea23c4 in unwind_cleanup () from /nix/store/m71p7f0nymb19yn1dascklyya2i96jfw-glibc-2.39-52/lib/libc.so.6
6 0x00007f56b9d2a1b8 in nix::triggerInterrupt() [clone .cold] () from /nix/store/sahgw550p621m9dy1pd7whl9c5g1g0p7-lix-2.90.0-rc1/lib/liblixutil.so
7 0x00007f56b990ac9d in std:🧵:_State_impl<std:🧵:_Invoker<std::tuple<nix::MonitorFdHup::MonitorFdHup(int)::{lambda()#1}> > >::_M_run() () from /nix/store/sahgw550p621m9dy1pd7whl9c5g1g0p7-lix-2.90.0-rc1/lib/liblixstore.so
8 0x00007f56b90e86d3 in execute_native_thread_routine () from /nix/store/c6r62m84hywf4i6qq1h28f13zv38yqyp-gcc-13.3.0-lib/lib/libstdc++.so.6
9 0x00007f56b8e99a42 in start_thread () from /nix/store/m71p7f0nymb19yn1dascklyya2i96jfw-glibc-2.39-52/lib/libc.so.6
10 0x00007f56b8f1905c in clone3 () from /nix/store/m71p7f0nymb19yn1dascklyya2i96jfw-glibc-2.39-52/lib/libc.so.6
As for testing, we've started a daemon with this change and verified it
deals with HUPs correctly on x86_64-linux, but I don't think we can
easily test the destructor behaviour without whatever Hydra was
doing that broke.
Change-Id: I29c7de0425674494b6e43c075810126c3ff77363
This also bans various sneaking of negative numbers from the language
into unsuspecting builtins as was exposed while auditing the
consequences of changing the Nix language integer type to a newtype.
It's unlikely that this change comprehensively ensures correctness when
passing integers out of the Nix language and we should probably add a
checked-narrowing function or something similar, but that's out of scope
for the immediate change.
During the development of this I found a few fun facts about the
language:
- You could overflow integers by converting from unsigned JSON values.
- You could overflow unsigned integers by converting negative numbers
into them when going into Nix config, into fetchTree, and into flake
inputs.
The flake inputs and Nix config cannot actually be tested properly
since they both ban thunks, however, we put in checks anyway because
it's possible these could somehow be used to do such shenanigans some
other way.
Note that Lix has banned Nix language integer overflows since the very
first public beta, but threw a SIGILL about them because we run with
-fsanitize=signed-overflow -fsanitize-undefined-trap-on-error in
production builds. Since the Nix language uses signed integers, overflow
was simply undefined behaviour, and since we defined that to trap, it
did.
Trapping on it was a bad UX, but we didn't even entirely notice
that we had done this at all until it was reported as a bug a couple of
months later (which is, to be fair, that flag working as intended), and
it's got enough production time that, aside from code that is IMHO buggy
(and which is, in any case, not in nixpkgs) such as
lix-project/lix#445, we don't think
anyone doing anything reasonable actually depends on wrapping overflow.
Even for weird use cases such as doing funny bit crimes, it doesn't make
sense IMO to have wrapping behaviour, since two's complement arithmetic
overflow behaviour is so *aggressively* not what you want for *any* kind
of mathematics/algorithms. The Nix language exists for package
management, a domain where bit crimes are already only dubiously in
scope to begin with, and it makes a lot more sense for that domain for
the integers to never lose precision, either by throwing errors if they
would, or by being arbitrary-precision.
This change will be ported to CppNix as well, to maintain language
consistency.
Fixes: lix-project/lix#423
Change-Id: I51f253840c4af2ea5422b8a420aa5fafbf8fae75
jade
alois31
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