Commit graph

2113 commits

Author SHA1 Message Date
jade 0cc285f87b
treewide: fix a bunch of lints
Fixes:
- Identifiers starting with _ are prohibited
- Some driveby header dependency cleaning which wound up with doing some
  extra fixups.
- Fucking C style casts, man. C++ made these 1000% worse by letting you
  also do memory corruption with them with references.
  - Remove casts to Expr * where ExprBlackHole is an incomplete type by
    introducing an explicitly-cast eBlackHoleAddr as Expr *.
  - An incredibly illegal cast of the text bytes of the StorePath hash
    into a size_t directly. You can't DO THAT.

    Replaced with actually parsing the hash so we get 100% of the bits
    being entropy, then memcpying the start of the hash. If this shows
    up in a profile we should just make the hash parser faster with a
    lookup table or something sensible like that.
  - This horrendous bit of UB which I thankfully slapped a deprecation
    warning on, built, and it didn't trigger anywhere so it was dead
    code and I just deleted it. But holy crap you *cannot* do that.

    inline void mkString(const Symbol & s)
    {
        mkString(((const std::string &) s).c_str());
    }
- Some wrong lints. Lots of wrong macro lints, one wrong
  suspicious-sizeof lint triggered by the template being instantiated
  with only pointers, but the calculation being correct for both
  pointers and not-pointers.
- Exceptions in destructors strike again. I tried to catch the
  exceptions that might actually happen rather than all the exceptions
  imaginable. We can let the runtime hard-kill it on other exceptions
  imo.

Change-Id: I71761620846cba64d66ee7ca231b20c061e69710
2024-08-26 16:13:03 -07:00
eldritch horrors b6884388a1 add dedicated test for hash mismatch url reporting
the current test relies on derivation build order being deterministic,
which will not be a reasonable expectation for all that long any more.

Change-Id: I9be44a7725185f614a9a4c724045b8b1e6962c03
2024-08-25 22:21:32 +00:00
jade 72f91767a8 Merge "fix: good errors for failures caused by allowSubstitutes" into main 2024-08-25 20:00:58 +00:00
eldritch horrors cae260a158 libstore: diagnose local build failure in goal
this should be done where we're actually trying to build something, not
in the main worker loop that shouldn't have to be aware of such details

Change-Id: I07276740c0e2e5591a8ce4828a4bfc705396527e
2024-08-25 19:55:47 +02:00
jade 686120ee4a fix: good errors for failures caused by allowSubstitutes
This caused an absolute saga which I would not like anyone else to have
to experience. Let's put in a laser targeted error message that
diagnoses this exact problem.

Fixes: #484
Change-Id: I2a79f04aeb4a1b67c10115e5e39501d958836298
2024-08-23 17:49:15 -07:00
alois31 e3c289dbe9
libutil/config: unify path setting types
There have been multiple setting types for paths that are supposed to be
canonicalised, depending on whether zero or one, one, or any number of paths is
to be specified. Naturally, they behaved in slightly different ways in the
code. Simplify things by unifying them and removing special behaviour (mainly
the "multiple paths type can coerce to boolean" thing).

Change-Id: I7c1ce95e9c8e1829a866fb37d679e167811e9705
2024-08-21 17:57:23 +02:00
piegames 0edfea450b libexpr: Soft-deprecate ancient let syntax
Change-Id: I6802b26f038578870ea1fa1ed298f0c4b1f29c4a
2024-08-21 12:59:03 +02:00
piegames 0a8888d1c7 treewide: Stop using ancient let syntax
Shows for how long these tests have not been touched by anyone …

Change-Id: I3d0c1209a86283ddb012db4e7d45073264fdd0eb
2024-08-21 06:55:52 +00:00
piegames 7210ed1b87 libexpr: Soft-deprecate __overrides
Change-Id: I787e69e1dad6edc5ccdb747b74a9ccd6e8e13bb3
2024-08-21 06:55:52 +00:00
Audrey Dutcher ac6974777e Merge "tests/functional/restricted: Don't use a process substitution" into main 2024-08-20 22:51:38 +00:00
Audrey Dutcher ae628d4af2 tests/functional/restricted: Don't use a process substitution
The <() process substitution syntax doesn't work for this one testcase
in bash for FreeBSD. The exact reason for this is unknown, possibly to
do with pipe vs file vs fifo EOF behavior. The prior behavior was this
test hanging forever, with no children of the bash process.

Change-Id: I71822a4b9dea6059b34300568256c5b7848109ac
2024-08-19 20:37:51 -07:00
Maximilian Bosch 040e783232 flake: don't refetch unmodified inputs by recursive follows
Closes #460

I managed to trigger the issue by having the following inputs (shortened):

    authentik-nix.url = "github:nix-community/authentik-nix";
    authentik-nix.inputs.poetry2nix.inputs.nixpkgs.follows = "nixpkgs";

When evaluating this using

    nix-eval-jobs --flake .#hydraJobs

I got the following error:

    error: cannot update unlocked flake input 'authentik-nix/poetry2nix' in pure mode

The issue we have here is that `authentik-nix/poetry2nix` was written
into the `overrideMap` which caused Nix to assume it's a new input and
tried to refetch it (#460) or errored out in pure mode
(nix-eval-jobs / Hydra).

The testcase unfortunately only involves checking for the output log
and makes sure that something *is* logged on the first fetch so that
the test doesn't rot when the logging changes since I didn't
manage to trigger the error above with the reproducer from #460. In
fact, I only managed to trigger the `cannot update unlocked flake input`
error in this context with `nix-eval-jobs`.

Change-Id: Ifd00091eec9a0067ed4bb3e5765a15d027328807
2024-08-19 19:57:12 +00:00
piegames 278fddc317 libexpr: Deprecate URL literals
Closes #437.

Change-Id: I9f67fc965bb4a7e7fd849e5067ac1cb3bab064cd
2024-08-17 20:31:57 +02:00
piegames 49d61b2e4b libexpr: Introduce Deprecated features
They are like experimental features, but opt-in instead of opt-out. They
will allow us to gracefully remove language features. See #437

Change-Id: I9ca04cc48e6926750c4d622c2b229b25cc142c42
2024-08-17 19:47:51 +02:00
piegames 1c080a8239 treewide: Stop using URL literals
They must die

Change-Id: Ibe2b1818b21d98ec1a68836d01d5dad729b8c501
2024-08-17 15:48:10 +00:00
jade b15d5cc6ee nix: remove explosions if you have a window size less than four
Turns out strings do not like being resized to -4.

This was discovered while messing with the tests to remove unbuffer and
trying stdbuf instead. Turns out that was not the right approach.

This basically rewrites the handling of this case to be much more
correct, and fixes a bug where with small window sizes where it would
ALSO truncate the attr names in addition to the optional descriptions.

Change-Id: Ifd1beeaffdb47cbb5f4a462b183fcb6c0ff6c524
2024-08-10 16:11:58 -07:00
jade 0c76195351 build: remove expect as a dependency
I was packaging Lix 2.91 for nixpkgs and was annoyed at the expect
dependency. Turns out that you can replace unbuffer with a pretty-short
Python script.

It became less short after I found out that Linux was converting \n to
\r\n in the terminal subsystem, which was not very funny, but is at
least solved by twiddling termios bits.

Change-Id: I8a2700abcbbf6a9902e01b05b40fa9340c0ab90c
2024-08-10 16:10:16 -07:00
jade 757041c3e7 Merge changes I526cceed,Ia4e2f1fa,I22e66972,I9fbd55a9,Ifca22e44 into main
* changes:
  sqlite: add a Use::fromStrNullable
  util: implement charptr_cast
  tree-wide: fix a pile of lints
  refactor: make HashType and Base enum classes for type safety
  build: integrate clang-tidy into CI
2024-08-08 22:43:10 +00:00
jade e34833c025 tree-wide: fix a pile of lints
This:
- Converts a bunch of C style casts into C++ casts.
- Removes some very silly pointer subtraction code (which is no more or
  less busted on i686 than it began)
- Fixes some "technically UB" that never had to be UB in the first
  place.
- Makes finally follow the noexcept status of the inner function. Maybe
  in the future we should ban the function from not being noexcept, but
  that is not today.
- Makes various locally-used exceptions inherit from std::exception.

Change-Id: I22e66972602604989b5e494fd940b93e0e6e9297
2024-08-08 14:53:17 -07:00
jade 370ac940dd refactor: make HashType and Base enum classes for type safety
Change-Id: I9fbd55a9d50464a56fe11cb42a06a206914150d8
2024-08-08 14:53:17 -07:00
piegames 28ae24f3f7 libexpr: Add experimental pipe operator
The |> operator is a reverse function operator with low binding strength
to replace lib.pipe. Implements RFC 148, see the RFC text for more
details. Closes #438.

Change-Id: I21df66e8014e0d4dd9753dd038560a2b0b7fd805
2024-08-08 11:13:53 +02:00
Max “Goldstein” Siling 6fdb47f0b2 Merge "src/libcmd/repl.cc: allow :log /path/to/store.drv" into main 2024-08-07 21:48:01 +00:00
piegames ec7552ff74 libexpr/parser: Test experimental features
Currently, the parser relies on the global experimental feature flags.
In order to properly test conditional language features, we instead need
to pass it around in the parser::State.

This means that the parser cannot cache the result of isEnabled anymore,
which wouldn't necessarily hurt performance if the function didn't
perform a linear search on the list of enabled features on every single
call. While we could simply evaluate once at the start of parsing and
cache the result in the parser state, the more sustainable solution
would be to fix `isEnabled` such that all callers may profit from the
performance improvement.

Change-Id: Ic9b9c5d882b6270e1114988b63e6064d36c25cf2
2024-08-07 13:07:50 +00:00
Max “Goldstein” Siling 9adfd9b8ad
src/libcmd/repl.cc: allow :log /path/to/store.drv
This adds a second form to the `:log` command: it now can accept a
derivation path in addition to a derivation expression. As derivation
store paths start with `/nix/store`, this is not ambiguous.

Resolves: #51
Change-Id: Iebc7b011537e7012fae8faed4024ea1b8fdc81c3
2024-08-07 15:58:44 +03:00
Maximilian Bosch 27a63db710 Merge "fix: warn and document when advanced attributes will have no impact due to __structuredAttrs" into main 2024-08-07 10:38:39 +00:00
jade ca9d3e6e00 tree-wide: fix various lint warnings
Change-Id: I0fc80718eb7e02d84cc4b5d5deec4c0f41116134
2024-08-04 20:55:45 -07:00
jade bd1344ec54 nix flake metadata: print modified dates for input flakes
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
2024-08-04 20:41:19 -07:00
jade 5f0ef50077 cli: eat terminal codes from stdout also
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
2024-08-04 20:41:19 -07:00
Tom Bereknyei 7fc481396c
fix: warn and document when advanced attributes will have no impact due to __structuredAttrs
Backport of https://github.com/NixOS/nix/pull/10884.

Change-Id: I82cc2794730ae9f4a9b7df0185ed0aea83efb65a
2024-08-03 13:32:51 +02:00
Isabel 9eb374dc6d Merge "nix flake show: add the description if it exists" into main 2024-08-02 07:56:06 +00:00
Maximilian Bosch 3bb8c627ae Merge "Reapply "libfetchers: make attribute / URL query handling consistent"" into main 2024-08-02 04:50:25 +00:00
Maximilian Bosch 87fd1f024c Reapply "libfetchers: make attribute / URL query handling consistent"
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] #419
[2] e22172aaf6b6a366cecd3c025590e68fa2b91bcc,
    originally 3e151d4d77

Change-Id: I2c72d5a32e406a7ca308e271730bd0af01c5d18b
2024-08-01 15:41:30 -07:00
jade 19ae87e5ce tree-wide: add support for asan!
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
2024-07-31 14:13:39 -07:00
Max “Goldstein” Siling 1a6d7a3af4 src/libcmd/repl.cc: avoid unneeded reload after :e
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: #341
Change-Id: I3747f75ce26e0595e953069c39ddc3ee80699718
2024-07-30 16:08:26 +00:00
alois31 e7188e211a
libstore/build: block io_uring
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
2024-07-25 18:24:45 +02:00
alois31 127ee1a101
libstore/build: use an allowlist approach to syscall filtering
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
2024-07-25 18:24:40 +02:00
Isabel d2422771eb
nix flake show: add the description if it exists
(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
2024-07-23 13:21:15 +01:00
jade 77ff799cc8 gc: refactor the gc server thread out into a class without changing it
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
2024-07-19 20:55:55 +00:00
alois31 40c39aa5d2
libexpr/print: do not show elided nested items when there are none
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
2024-07-18 18:41:34 +02:00
alois31 b5da823138
libexpr/print: never show empty attrsets or derivations as «repeated»
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
2024-07-18 18:41:34 +02:00
alois31 81a0624d76
libexpr/print: pretty-print idempotently
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
2024-07-18 18:41:28 +02:00
Max “Goldstein” Siling 68567206f2 Merge "tests/functional/repl.sh: actually fail test on wrong stdout" into main 2024-07-17 21:50:59 +00:00
Max “Goldstein” Siling 3a36c8bb90 tests/functional/repl.sh: actually fail test on wrong stdout
Previous test implementation assumed that grep supports newlines
in patterns. It doesn't, so tests spuriously passed, even though
some tests outputs were broken.

This patches output (and expected output) before grepping,
so there're no newlines in pattern.

Change-Id: Ie6561f9f2e18b83d976f162269d20136e2595141
2024-07-17 21:48:13 +00:00
eldritch horrors 6b4d46e9e0 libstore: remove WriteConn::sink fields
we no longer need these since we're no longer using sinks to serialize things.

Change-Id: Iffb1a3eab33c83f611c88fa4e8beaa8d5ffa079b
2024-07-16 00:57:42 +00:00
eldritch horrors a5d1f69841 libstore: generatorize protocol serializers
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
2024-07-16 00:57:42 +00:00
Qyriad ae7eab49b9 nix3-upgrade-nix: always use the /new/ nix-env to perform the installation
Fixes #411.

Change-Id: I8d87c0e9295deea26ff33234e15ee33cc68ab303
2024-07-15 15:26:53 -06:00
jade 917c9bdee7 language: cleanly ban integer overflows
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
#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: #423

Change-Id: I51f253840c4af2ea5422b8a420aa5fafbf8fae75
2024-07-13 00:59:33 +02:00
jade f9641b9efd libutil: add checked arithmetic tools
This is in preparation for adding checked arithmetic to the evaluator.

Change-Id: I6e115ce8f5411feda1706624977a4dcd5efd4d13
2024-07-13 00:56:37 +02:00
eldritch horrors df8851f286 libutil: rewrite RewritingSink as source
the rewriting sink was just broken. when given a rewrite set that
contained a key that is also a proper infix of another key it was
possible to produce an incorrectly rewritten result if the writer
used the wrong block size. fixing this duplicates rewriteStrings,
to avoid this we'll rewrite rewriteStrings to use RewritingSource
in a new mode that'll allow rewrites we had previously forbidden.

Change-Id: I57fa0a9a994e654e11d07172b8e31d15f0b7e8c0
2024-07-11 11:39:18 +00:00
Quantum Jump 6e0ca02425 Fix dry-run flag for nix-collect-garbage
`nix-collect-garbage --dry-run` previously elided the entire garbage
collection check, meaning that it would just exit the script without
printing anything.

This change makes the dry run flag instead set the GC action to
`gcReturnDead` rather than `gcDeleteDead`, and then continue with the
script. So if you set `--dry-run`, it will print the paths it *would*
have garbage collected, but not actually delete them.

I filed a bug for this: #432 but then realised I could give fixing it a go myself.

Change-Id: I062dbf1a80bbab192b5fd0b3a453a0b555ad16f2
2024-07-09 13:55:05 +00:00