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2116 commits

Author SHA1 Message Date
jade 9896d309cb Revert "libexpr: Replace regex engine with boost::regex"
This reverts commit 447212fa65.

Reason for revert: Regression in eval behaviour bug-compatibility.

Expected behaviour (Nix 2.18.5, macOS and Linux [libstdc++/libc++]):

```
nix-repl> builtins.match "\\.*(.*)" ".keep"
[ "keep" ]

nix-repl> builtins.match "(\\.*)(.*)" ".keep"
[ "." "keep" ]
```

Actual behaviour (boost::regex):

```
nix-repl> builtins.match "\\.*(.*)" ".keep"
[ ".keep" ]

nix-repl> builtins.match "(\\.*)(.*)" ".keep"
[
  "."
  "keep"
]
```

Bug: lix-project/lix#483
Change-Id: Id462eb8586dcd54856cf095f09b3e3a216955b60
2024-08-22 18:35:11 +00:00
sugar🍬🍭🏳️‍⚧️ 447212fa65 libexpr: Replace regex engine with boost::regex
This avoids C++'s standard library regexes, which aren't the same
across platforms, and have many other issues, like using stack
so much that they stack overflow when processing a lot of data.

To avoid backwards and forward compatibility issues, regexes are
processed using a function converting libstdc++ regexes into Boost
regexes, escaping characters that Boost needs to have escaped, and
rejecting features that Boost has and libstdc++ doesn't.

Related context:

- Original failed attempt to use `boost::regex` in CppNix, failed due to
  boost icu dependency being large (disabling ICU is no longer necessary
  because linking ICU requires using a different header file,
  `boost/regex/icu.hpp`): https://github.com/NixOS/nix/pull/3826

- An attempt to use PCRE, rejected due to providing less backwards
  compatibility with `std::regex` than `boost::regex`:
  https://github.com/NixOS/nix/pull/7336

- Second attempt to use `boost::regex`, failed due to `}` regex failing
  to compile (dealt with by writing a wrapper that parses a regular
  expression and escapes `}` characters):
  https://github.com/NixOS/nix/pull/7762

Closes #34. Closes #476.

Change-Id: Ieb0eb9e270a93e4c7eed412ba4f9f96cb00a5fa4
2024-08-22 03:17:55 +02:00
jade 84543b459c doc: fix broken meson deps for various manuals outputs
This is incredibly haunted, but it can happen that you change libutil,
breaking the generation of the .json files, which then does not rebuild
the files. I don't expect they are slow to build, so it does not seem so
bad to just rebuild them every time instead of extracting a list of all
the possible deps.

We want to delete this nonsense anyway and replace it with generated
code.

Change-Id: Ia576d1a3bdee48fbaefbb5ac194354428d179a84
2024-08-18 15:19:15 -07:00
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
jade 7e0fee5309 release: release notes for 2.91.0
Release created with releng/create_release.xsh

Change-Id: Ieb6ca02d3cf986b28440fce3792e8c38ce80a33e
2024-08-12 16:04:22 -07:00
jade 7ca47a0e69 rl-next: add extra context to a few release notes
This was found while writing the release blog post.

Change-Id: Ifd55f308d4d4c831273cbe6ea35d29a38e134783
2024-08-09 23:22:11 -07:00
jade 35c9069c66 rl-next: fix incorrect CL list syntax
This also fixes the script to not pass pre-commit by failing to parse an
int if this mistake is made again.

Change-Id: I714369f515dc9987cf0c600d54a2ac745ba56830
2024-08-09 19:03:08 -07:00
eldritch horrors 35a2f28a46 libstore: deprecate the build-hook setting
implementing a build hook is pretty much impossible without either being
a nix, or blindly forwarding the important bits of all build requests to
some kind of nix. we've found no uses of build-hook in the wild, and the
build-hook protocol (apart from being entirely undocumented) is not able
to convey any kind of versioning information between hook and daemon. if
we want to upgrade this infrastructure (which we do), this must not stay

Change-Id: I1ec4976a35adf8105b8ca9240b7984f8b91e147e
2024-08-09 19:30:45 +00:00
jade 790d1079e1 Merge changes Ib7c80826,I636f8a71,I67669b98 into main
* changes:
  perl: un-autos your conf
  build: declare all the deps as -isystem
  darwin: workaround PROC_PIDLISTFDS on processes with no fds
2024-08-09 19:24:29 +00:00
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
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: lix-project/lix#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 1437d3df15 darwin: workaround PROC_PIDLISTFDS on processes with no fds
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
2024-08-07 02:52:00 -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
jade 378ec5fb06 Implement forcing CLI colour on, and document it better
This is necessary to make some old tests work when testing colour
against non-interactive outputs.

Change-Id: Id89f8a1f45c587fede35a69db85f7a52f2c0a981
2024-08-04 20:41:19 -07:00
jade 700762d8b2 manual: fix a syntax error in redirects.js that made it not do anything
lol lmao

Let's put in a syntax checker in CI so we do not have to deal with this
nonsense ever again.

Change-Id: I0fe875e0cfc59ab1783087762e5bb07e09ded105
2024-08-04 20:41:19 -07:00
jade 0f998056fa misc docs/meson tidying
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
2024-08-04 20:41:19 -07:00
jade 3daeeaefb1 build: implement clang-tidy using our plugin
The principle of this is that you can either externally build it with
Nix (actual implementation will be in a future commit), or it can be
built with meson if the Nix one is not passed in.

The idea I have is that dev shells don't receive the one from Nix to
avoid having to build it, but CI can use the one from Nix and save some
gratuitous rebuilds.

The design of this is that you can run `ninja -C build clang-tidy` and
it will simply correctly clang-tidy the codebase in spite of PCH
bullshit caused by the cc-wrapper.

This is a truly horrendous number of hacks in a ball, caused by bugs in
several pieces of software, and I am not even getting started.

I don't consider this to fix the clang-tidy issue filing, since we still
have a fair number of issues to fix even on the existing minimal
configuration, and I have not yet implemented it in CI. Realistically we
will need to do something like https://github.com/Ericsson/codechecker
to be able to silence warnings without physically touching the code, or
at least *diff* reports between versions.

Also, the run-clang-tidy output design is rather atrocious and must
not be inflicted upon anyone I have respect for, since it buries the
diagnostics in a pile of invocation logs. We would do really well to
integrate with the Gerrit SARIF stuff so we can dump the reports on
people in a user-friendly manner.

Related: lix-project/lix#147

Change-Id: Ifefe533f3b56874795de231667046b2da6ff2461
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
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: lix-project/lix#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
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 22252825c4 Merge changes Id8b3d289,Ib75ab5b8,I3792eeb3 into main
* 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
2024-07-19 18:52:46 +00:00
alois31 aba5f19680 Merge changes I829581a3,I0016970d,I5dac8e77,Ib7560fe5 into main
* 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
2024-07-19 06:40:13 +00:00
jade 26e56780ca Fixup a bunch of references to nixos.org manuals
(plus one reference to CppNix github)

Change-Id: Id8b3d2897f3b54e286861805cfd421adc4d5de47
2024-07-18 19:27:33 +00:00
jade 10cc3b288d Add release notes for removing overflow from Nix language
Change-Id: Ib75ab5b8b4d879035d7ee7678f9cd0c491a39c0a
2024-07-18 19:27:33 +00:00
jade 5ee1e6ea98 Merge changes Ib20e9aa0,I178a038b,I29c7de04 into main
* 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"
2024-07-18 17:40:32 +00:00
alois31 768d1f29a2
doc/release-notes: add for pretty printing improvements
Change-Id: I829581a3f5b8b742e6c866dcdbbc635f91afceb5
2024-07-18 19:08:20 +02:00
alois31 7b1abf8107 Merge "doc/manual: clarify documentation related to the $$ parser bug" into main 2024-07-18 15:01:20 +00:00
alois31 72db9cd67b doc/release-notes: link the upcoming release notes again
The insertion marker comment broke the list into two parts, the first
containing only the link to the upcoming release notes and the second the
past releases. This confused the generator, leading to the first part being
discarded. Indent the marker comment so that it's syntactically part of the
preceding item, and in particular doesn't split the list any more.

Change-Id: I357c51bb03e4e0d79a76d30158615fd9eda95ea8
2024-07-17 22:12:41 +00:00
raito 67f62bcdb4 doc/release-notes: add date for major release
Change-Id: I93aab93c069bb3989c3f8d17e0862899e6f76865
Signed-off-by: Raito Bezarius <raito@lix.systems>
2024-07-17 22:12:41 +00:00
alois31 beb231784e doc/manual: clarify documentation related to the $$ parser bug
Due to a mistake in the grammar, a dollar character implicitly escapes a second
dollar character that immediately follows, so that it cannot start an
interpolation. Unfortunately, this behaviour has since come to be relied upon,
so it cannot be fixed. Furthermore, the documentation on regular strings did
not mention this behaviour at all, while in the case of indented strings it was
rather implicit.
Mention it explicitly in both cases, and describe how an interpolation can
follow a dollar character (namely, by escaping that). Since we have to touch
that section anyway, state that any character (other than n, r, and t; but
notably including `$` even if not succeeded by `{`) can be escaped using a
backslash in regular strings.

Change-Id: I7e5d68a9a4130eec98ce8218b485168f4b31a677
2024-07-17 22:01:48 +00:00
jade 702f02c31f docs: document the actual comparison rules instead of lies
Although the comparison rules are ugly and we do not like various parts
of them, we must not hide them away for only catgirls to know about, so
the documentation should actually say how they work.

Change-Id: Ib20e9aa0e7b6486ade4f401035aafd85fbb08c91
2024-07-13 01:17:14 +02:00
jade a8f443d960 docs: update to define integer overflow
Change-Id: Ie8a1b31035f2d27a220e5df2e9e178ec3b39ee68
2024-07-13 00:59:33 +02:00
eldritch horrors f0c751d4d6 Merge changes I81552018,Ieb65c133 into main
* changes:
  releng: add releaseTests flake output, test script
  add aarch64-linux as a cross-build target
2024-07-10 17:45:17 +00:00
eldritch horrors 4d8c66ec6f add aarch64-linux as a cross-build target
we want to be sure we can cross-build to aarch64 for releases, add a
target to our crossSystems list to make those cheacks easier to run.

Change-Id: Ieb65c1333a5232641ace0ba4d122fc7d528ebc04
2024-07-09 22:49:10 +02:00
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: lix-project/lix#432 but then realised I could give fixing it a go myself.

Change-Id: I062dbf1a80bbab192b5fd0b3a453a0b555ad16f2
2024-07-09 13:55:05 +00:00
Qyriad 4c7165be86 distinguish between throws & errors during throw
Turns errors like this:

let
  throwMsg = a: throw (a + " invalid bar");
in throwMsg "bullshit"

error:
       … from call site
         at «string»:3:4:
            2|   throwMsg = a: throw (a + " invalid bar");
            3| in throwMsg "bullshit"
             |    ^

       … while calling 'throwMsg'
         at «string»:2:14:
            1| let
            2|   throwMsg = a: throw (a + " invalid bar");
             |              ^
            3| in throwMsg "bullshit"

       … while calling the 'throw' builtin
         at «string»:2:17:
            1| let
            2|   throwMsg = a: throw (a + " invalid bar");
             |                 ^
            3| in throwMsg "bullshit"

       error: bullshit invalid bar

into errors like this:

let
  throwMsg = a: throw (a + " invalid bar");
in throwMsg "bullshit"

error:
       … from call site
         at «string»:3:4:
            2|   throwMsg = a: throw (a + " invalid bar");
            3| in throwMsg "bullshit"
             |    ^

       … while calling 'throwMsg'
         at «string»:2:14:
            1| let
            2|   throwMsg = a: throw (a + " invalid bar");
             |              ^
            3| in throwMsg "bullshit"

       … caused by explicit throw
         at «string»:2:17:
            1| let
            2|   throwMsg = a: throw (a + " invalid bar");
             |                 ^
            3| in throwMsg "bullshit"

       error: bullshit invalid bar

Change-Id: I593688928ece20f97999d1bf03b2b46d9ac338cb
2024-07-04 17:43:03 -06:00
Qyriad 14bf54bd39 trace which part of foo.bar.baz errors
Turns errors like:

let
  somepkg.src = throw "invalid foobar";
in somepkg.src.meta

error:
       … while evaluating the attribute 'src.meta'
         at «string»:2:3:
            1| let
            2|   somepkg.src = throw "invalid foobar";
             |   ^
            3| in somepkg.src.meta

       … while calling the 'throw' builtin
         at «string»:2:17:
            1| let
            2|   somepkg.src = throw "invalid foobar";
             |                 ^
            3| in somepkg.src.meta

       error: invalid foobar

into errors like:

let
  somepkg.src = throw "invalid foobar";
in somepkg.src.meta

error:
       … while evaluating the attribute 'src.meta'
         at «string»:2:3:
            1| let
            2|   somepkg.src = throw "invalid foobar";
             |   ^
            3| in somepkg.src.meta

       … while evaluating 'somepkg.src' to select 'meta' on it
         at «string»:3:4:
            2|   somepkg.src = throw "invalid foobar";
            3| in somepkg.src.meta
             |    ^

       … while calling the 'throw' builtin
         at «string»:2:17:
            1| let
            2|   somepkg.src = throw "invalid foobar";
             |                 ^
            3| in somepkg.src.meta

       error: invalid foobar

And for type errors, from:

let
  somepkg.src = "I'm not an attrset";
in somepkg.src.meta

error:
       … while evaluating the attribute 'src.meta'
         at «string»:2:3:
            1| let
            2|   somepkg.src = "I'm not an attrset";
             |   ^
            3| in somepkg.src.meta

       … while selecting an attribute
         at «string»:3:4:
            2|   somepkg.src = "I'm not an attrset";
            3| in somepkg.src.meta
             |    ^

       error: expected a set but found a string: "I'm not an attrset"

into:

let
  somepkg.src = "I'm not an attrset";
in somepkg.src.meta

error:
       … while evaluating the attribute 'src.meta'
         at «string»:2:3:
            1| let
            2|   somepkg.src = "I'm not an attrset";
             |   ^
            3| in somepkg.src.meta

       … while selecting 'meta' on 'somepkg.src'
         at «string»:3:4:
            2|   somepkg.src = "I'm not an attrset";
            3| in somepkg.src.meta
             |    ^

       error: expected a set but found a string: "I'm not an attrset"

For the low price of an enumerate() and a lambda you too can have the
incorrect line of code actually show up in the trace!

Change-Id: Ic1491c86e33c167891bdac9adad6224784760bd6
2024-07-04 17:42:35 -06:00
Qyriad d00edfb28d trace when the foo part of foo.bar.baz errors
Turns errors like:

let
  errpkg = throw "invalid foobar";
in errpkg.meta

error:
       … while calling the 'throw' builtin
         at «string»:2:12:
            1| let
            2|   errpkg = throw "invalid foobar";
             |            ^
            3| in errpkg.meta

       error: invalid foobar

into errors like:

let
  errpkg = throw "invalid foobar";
in errpkg.meta

error:
       … while evaluating 'errpkg' to select 'meta' on it
         at «string»:3:4:
            2|   errpkg = throw "invalid foobar";
            3| in errpkg.meta
             |    ^

       … while calling the 'throw' builtin
         at «string»:2:12:
            1| let
            2|   errpkg = throw "invalid foobar";
             |            ^
            3| in errpkg.meta

       error: invalid foobar

For the low price of one try/catch, you too can have the incorrect line
of code actually show up in the trace!

Change-Id: If8d6200ec1567706669d405c34adcd7e2d2cd29d
2024-07-04 16:33:02 -06:00
Delan Azabani 865a3732fa Merge "Reject fully-qualified URLs in 'from' argument of nix registry add" into main 2024-07-02 07:20:01 +00:00
jade d3286d0990 Merge changes Ie29a8a89,I873eedcf into main
* changes:
  store: delete obsolete lsof-disabling code
  store: guess the URL of failing fixed-output derivations
2024-07-01 16:11:32 +00:00
alois31 a55112898e
libexpr/flake: allow automatic rejection of configuration options from flakes
The `allow-flake-configuration` option allows the user to control whether to
accept configuration options supplied by flakes. Unfortunately, setting this
to false really meant "ask each time" (with an option to remember the choice
for each specific option encountered). Let no mean no, and introduce (and
default to) a separate value for the "ask each time" behaviour.

Co-Authored-By: Jade Lovelace <lix@jade.fyi>
Change-Id: I7ccd67a95bfc92cffc1ebdc972d243f5191cc1b4
2024-06-30 19:28:14 +02:00
Delan Azabani b2944d93a6 Reject fully-qualified URLs in 'from' argument of nix registry add
We previously allowed you to map any flake URL to any other flake URL,
including shorthand flakerefs, indirect flake URLs like `flake:nixpkgs`,
direct flake URLs like `github:NixOS/nixpkgs`, or local paths.

But flake registry entries mapping from direct flake URLs often come
from swapping the 'from' and 'to' arguments by accident, and even when
created intentionally, they may not actually work correctly.

This patch rejects those URLs (and fully-qualified flake: URLs), making
it harder to swap the arguments by accident.

Fixes #181.

Change-Id: I24713643a534166c052719b8770a4edfcfdb8cf3
2024-06-29 05:11:31 +00:00
jade d85309f7ca store: delete obsolete lsof-disabling code
Since Ifa0adda7984e, we don't use this code anymore on macOS, so we have
no reason to have a knob to disable it anymore.

Change-Id: Ie29a8a8978d9aefd4551895f4f9b3cc0827496df
2024-06-27 22:53:36 -07:00
jade d92712673b store: guess the URL of failing fixed-output derivations
This is a shameless layering violation in favour of UX. It falls back
trivially to "unknown", so it's purely a UX feature.

Diagnostic sample:

```
error: hash mismatch in fixed-output derivation '/nix/store/sjfw324j4533lwnpmr5z4icpb85r63ai-x1.drv':
        likely URL: https://meow.puppy.forge/puppy.tar.gz
         specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
            got:    sha256-a1Qvp3FOOkWpL9kFHgugU1ok5UtRPSu+NwCZKbbaEro=
```

Change-Id: I873eedcf7984ab23f57a6754be00232b5cb5b02c
2024-06-27 22:44:16 -07:00