Commit graph

3957 commits

Author SHA1 Message Date
Simon Rainerson
31a6e10fe5 Fix misread of source if path is already valid
When receiving a stream of NARs through the ssh-ng protocol, an already
existing path would cause the NAR archive to not be read in the stream,
resulting in trying to parse the NAR as a ValidPathInfo. This results in
the error message:
    error: not an absolute path: 'nix-archive-1'

Fixes #6253

Usually this problem is avoided by running QueryValidPaths before
AddMultipleToStore, but can arise when two parallel nix processes gets
the same response from QueryValidPaths. This makes the problem more
prominent when running builds in parallel.
2023-08-07 10:27:40 +02:00
John Ericson
9113b4252b
Merge pull request #8760 from iFreilicht/fix-json-load-assertion-errors
Fix derivation load assertion errors
2023-08-06 17:07:43 -07:00
Felix Uhl
3fefc2b284 Fix derivation load assertion errors
When loading a derivation from a JSON, malformed input would trigger
cryptic "assertion failed" errors. Simply replacing calls to `operator []`
with calls to `.at()` was not enough, as this would cause json.execptions
to be printed verbatim.

Display nice error messages instead and give some indication where the
error happened.

*Before:*

```
$ echo 4 | nix derivation add
error: [json.exception.type_error.305] cannot use operator[] with a string argument with number

$ nix derivation show nixpkgs#hello | nix derivation add
Assertion failed: (it != m_value.object->end()), function operator[], file /nix/store/8h9pxgq1776ns6qi5arx08ifgnhmgl22-nlohmann_json-3.11.2/include/nlohmann/json.hpp, line 2135.

$ nix derivation show nixpkgs#hello | jq '.[] | .name = 5' | nix derivation add
error: [json.exception.type_error.302] type must be string, but is object

$ nix derivation show nixpkgs#hello | jq '.[] | .outputs = { out: "/nix/store/8j3f8j-hello" }' | nix derivation add
error: [json.exception.type_error.302] type must be object, but is string

```

*After:*

```
$ echo 4 | nix derivation add
error: Expected JSON of derivation to be of type 'object', but it is of type 'number'

$ nix derivation show nixpkgs#hello | nix derivation add
error: Expected JSON object to contain key 'name' but it doesn't

$ nix derivation show nixpkgs#hello | jq '.[] | .name = 5' | nix derivation add
error: Expected JSON value to be of type 'string' but it is of type 'number'

$ nix derivation show nixpkgs#hello | jq '.[] | .outputs = { out: "/nix/store/8j3f8j-hello" }' | nix derivation add
error:
       … while reading key 'outputs'

       error: Expected JSON value to be of type 'object' but it is of type 'string'
```
2023-08-05 01:34:30 +02:00
John Ericson
3b592c880a Add infra for experimental store implemenations
This is analogous to that for experimental settings and flags that we
have also added as of late.
2023-08-02 15:46:38 -04:00
John Ericson
66550878df Add comment explaining the use of readDirectory(realStoreDir) 2023-08-02 12:46:07 -04:00
John Ericson
770d50e49c local-store verifying: Rename store to something more clear
It is not a `Store` but a `StorePathSet`.
2023-08-02 12:40:04 -04:00
John Ericson
6525265f46 LocalStore::verifyPath: Try to clarify data flow with more scopes
It was initially unclear to me which of these are temporary state for
the verify paths computation, and which of these are the results of that
computation to be used in the rest of the function. Now, it is clear,
and enforced.
2023-07-31 12:44:27 -04:00
John Ericson
2a5f5fbb17 LocalStore::verifyPath: Use StorePathSet for store local var
We don't care about non-store-paths in there (things like `.links`, are,
in fact, allowed). So let's just skip them up front and be more strongly
typed.
2023-07-31 12:44:18 -04:00
Ben Radford
c9a87ce7ca Refactor verifyPath to take StorePath instead of Path.
This way we avoid having to convert from Path to StorePath and vice versa in
the body of verifyPath.
2023-07-31 11:17:55 -04:00
John Ericson
60d8dd7aea Clean up store hierarchy with IndirectRootStore
See the API doc comments for details.
2023-07-24 09:19:44 -04:00
John Ericson
13269ba93b Make RemoteStore::ConnectionHandle part of class and expose
Will need to do subclass-specific implementations in the next commit.
This isn't because there will be multiple variations of the daemon
protocol (whew!) but because different clients pick and choose different
parts to use.
2023-07-24 09:17:01 -04:00
John Ericson
0a30b07277 Move Store::Params typedef to StoreConfig::Params
This is because `StoreConfig` also uses it.
2023-07-24 09:03:44 -04:00
John Ericson
fe1fbdb5a1
Merge pull request #8724 from obsidiansystems/queryPartialDerivationOutputMap-evalStore
Give `queryPartialDerivationOutputMap` an `evalStore` parameter
2023-07-21 08:53:18 -04:00
Eelco Dolstra
7ac24d9525
Merge pull request #8650 from obsidiansystems/content-address-simpler
Simplify `ContentAddress`
2023-07-21 13:46:53 +02:00
John Ericson
6bc98c7fba Give queryPartialDerivationOutputMap an evalStore parameter
This makes it more useful. In general, the derivation will be in one
store, and the realisation info is in another.

This also helps us avoid duplication. See how `resolveDerivedPath` is
now simpler because it uses `queryPartialDerivationOutputMap`. In #8369
we get more flavors of derived path, and need more code to resolve them
all, and this problem only gets worse.

The fact that we need a new method to deal with the multiple dispatch is
unfortunate, but this generally relates to the fact that `Store` is a
sub-par interface, too bulky/unwieldy and conflating separate concerns.
Solving that is out of scope of this PR.

This is part of the RFC 92 work. See tracking issue #6316
2023-07-20 15:59:52 -04:00
John Ericson
f62543fe1c Remove unneeded copy
It appeared in 8eb73a8724 (by me!) without
justification.
2023-07-20 15:42:06 -04:00
John Ericson
7b30293d38 Tighten #includes: DerivedPath doesn't care about Realisation 2023-07-20 15:42:06 -04:00
Robert Hensing
32494cbb29
Merge pull request #7973 from fricklerhandwerk/remove-channels
remove the Channels section
2023-07-19 14:02:26 +02:00
Valentin Gagarin
2fa90e5824 add more details on CA derivations 2023-07-19 13:59:18 +02:00
Valentin Gagarin
5f37ebcf83 document all special system features and their behavior 2023-07-19 13:34:03 +02:00
Robert Hensing
eca07b2a47
Merge pull request #8315 from fricklerhandwerk/doc-system
add information on the system type string
2023-07-19 12:07:23 +02:00
Valentin Gagarin
493ddf617f reformat system-features setting documentation 2023-07-19 11:07:47 +02:00
Valentin Gagarin
feb01b22ed add links to store API documentation 2023-07-19 11:07:47 +02:00
Valentin Gagarin
6c3cd429a6 fix broken links 2023-07-19 11:01:48 +02:00
Valentin Gagarin
0779005f49 expand on the extra-platforms option 2023-07-19 10:57:37 +02:00
Valentin Gagarin
fcadac0a02 mention extra-platforms 2023-07-19 10:38:42 +02:00
Valentin Gagarin
aba32def73 fix wording
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
2023-07-19 10:38:30 +02:00
Valentin Gagarin
32de11923e add cross-links 2023-07-19 10:37:40 +02:00
Valentin Gagarin
3763c7bb5e shorten system setting description 2023-07-19 10:37:40 +02:00
Valentin Gagarin
c8a42039ea move docs of the current system to the system setting
add information what happens when Nix itself is cross-compiled
2023-07-19 10:37:40 +02:00
Valentin Gagarin
0751c1bfc6 one line per sentence for easier review 2023-07-19 10:37:40 +02:00
Robert Hensing
0e3a7e34a0
Merge pull request #8506 from corngood/ssh-master
Pass NIX_SSHOPTS when checking for an ssh master connection.
2023-07-18 15:47:57 +02:00
Théophane Hufschmitt
a8d5bb5e7e
Merge pull request #8342 from NixLayeredStore/best-effort-supplementary-groups
Best effort supplementary groups
2023-07-17 20:58:17 +02:00
John Ericson
0f7242ff87 Test nested sandboxing, and make nicer error
We were bedeviled by sandboxing issues when working on the layered
store. The problem ended up being that when we have nested nix builds,
and the inner store is inside the build dir (e.g. store is
`/build/nix-test/$name/store`, build dir is `/build`) bind mounts
clobber each other and store paths cannot be found.

After thoroughly cleaning up `local-derivation-goal.cc`, we might be
able to make that work. But that is a lot of work. For now, we just fail
earlier with a proper error message.

Finally, test this: nested sandboxing without the problematic store dir
should work, and with should fail with the expected error message.

Co-authored-by: Dylan Green <67574902+cidkidnix@users.noreply.github.com>
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
2023-07-14 09:40:24 -04:00
John Ericson
caabc4f648 Feature gate DownstreamPlaceholder::unknownCaOutput
This is a part of CA derivations that we forgot to put behind the
experimental feature.

This was caught by @fricklerhandwerk in
https://github.com/NixOS/nix/pull/8369#discussion_r1258133719
2023-07-13 07:56:33 -04:00
John Ericson
2c3fb0eb33 Move BuiltPath to its own header/C++ file in libcmd
It is less important, and used less widely, than `DerivedPath`.
2023-07-12 23:01:10 -04:00
Ben Radford
a2acd23466
Update src/libstore/globals.hh
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
2023-07-12 12:33:05 +01:00
Ben Radford
0309f6b5b8
Update src/libstore/globals.hh
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
2023-07-12 12:32:57 +01:00
Ben Radford
b8e8dfc3e8
Say a bit about default value in setting description. 2023-07-11 11:25:49 +01:00
Ben Radford
a193ec4052
Default should depend on whether we are root. 2023-07-11 11:14:13 +01:00
Ben Radford
2b4c59dd99
Be clearer about the security implications. 2023-07-11 11:09:25 +01:00
Ben Radford
0caf28f238
Update description for require-drop-supplementary-groups. 2023-07-11 10:57:14 +01:00
Ben Radford
07dabcc90e
Always attempt setgroups but allow failure to be ignored. 2023-07-11 10:44:05 +01:00
Ben Radford
25b20b4ad2
Merge remote-tracking branch 'origin/master' into best-effort-supplementary-groups 2023-07-11 09:38:34 +01:00
John Ericson
903700c5e1 Simplify ContentAddress
Whereas `ContentAddressWithReferences` is a sum type complex because different
varieties support different notions of reference, and
`ContentAddressMethod` is a nested enum to support that,
`ContentAddress` can be a simple pair of a method and hash.

`ContentAddress` does not need to be a sum type on the outside because
the choice of method doesn't effect what type of hashes we can use.

Co-Authored-By: Cale Gibbard <cgibbard@gmail.com>
2023-07-07 07:30:01 -04:00
Robert Hensing
55888633dd makeContentAddressed: Add single path helper 2023-06-30 18:22:47 +02:00
Yueh-Shun Li
eebfe989a5 linkOrCopy: Fallback upon cross-device link error (EXDEV)
Fix building derivations in local chroot store on OpenAFS,
where hard linking accross directories causes cross-device link error
(EXDEV).
2023-06-30 21:12:26 +08:00
Jean-François Roche
80c9259756 Allow to sign path as unprivileged user
User can now sign path as unprivileged/allowed user

refs #1708
2023-06-27 18:31:31 +02:00
Robert Hensing
fd4f03b8fd
Merge pull request #8519 from fricklerhandwerk/reword-trusted-users
reword documentation on trusted users and substituters
2023-06-23 13:08:46 +02:00
John Ericson
97df060588 Better document build failure exit codes
- Improved API docs from comment

- Exit codes are for `nix-build`, not just `nix-store --release`

- Make note in tests so the magic numbers are not surprising

Picking up where #8387 left off.
2023-06-22 14:29:45 -04:00
John Ericson
48fe0ed554
Merge pull request #8374 from obsidiansystems/improve-path-setting
Split `OptionalPathSetting` from `PathSetting`
2023-06-21 15:40:43 -04:00
Eelco Dolstra
b1352700c4
Merge pull request #8552 from edolstra/fix-eagain
GC server: Clear O_NONBLOCK on the right file descriptor
2023-06-20 12:12:53 +02:00
Ben Radford
6ae35534b7
Support opening local store with database on read-only filesystem (#8356)
Previously it was not possible to open a local store when its database is on a read-only filesystem. Obviously a store on a read-only filesystem cannot be modified, but it would still be useful to be able to query it.

This change adds a new read-only setting to LocalStore. When set to true, Nix will skip operations that fail when the database is on a read-only filesystem (acquiring big-lock, schema migration, etc), and the store database will be opened in immutable mode.

Co-authored-by: Ben Radford <benradf@users.noreply.github.com>
Co-authored-by: cidkidnix <cidkidnix@protonmail.com>
Co-authored-by: Dylan Green <67574902+cidkidnix@users.noreply.github.com>
Co-authored-by: John Ericson <git@JohnEricson.me>
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
2023-06-20 11:34:09 +02:00
Eelco Dolstra
a6a75ecad8 GC server: Clear O_NONBLOCK on the right file descriptor
The bug fix in 6d30f9e6fe erroneously
cleared O_NONBLOCK on the server rather than client FD (leaving both
in an incorrect state).

Fixes #8551.
2023-06-20 11:19:14 +02:00
John Ericson
3859cf6b21 Remove unused #include from local-derivation-goal.cc
These were never needed for this file, and date back to before this was
split from `derivation-goal.cc`.
2023-06-19 12:18:04 -04:00
John Ericson
9f69b7dee9 Create worker_proto::{Read,Write}Conn
Pass this around instead of `Source &` and `Sink &` directly. This will
give us something to put the protocol version on once the time comes.

To do this ergonomically, we need to expose `RemoteStore::Connection`,
so do that too. Give it some more API docs while we are at it.
2023-06-19 12:08:23 -04:00
John Ericson
4e8b495ad7 Likewise namespace and enum struct-ify ServeCommand
The motivation is exactly the same as for the last commit. In addition,
this anticipates us formally defining separate serialisers for the serve
protocol.
2023-06-19 12:08:23 -04:00
John Ericson
95eae0c002 Put worker protocol items inside a WorkerProto struct
See API docs on that struct for why. The pasing as as template argument
doesn't yet happen in that commit, but will instead happen in later
commit.

Also make `WorkerOp` (now `Op`) and enum struct. This led us to catch
that two operations were not handled!

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
2023-06-19 12:08:23 -04:00
John Ericson
469d06f9bc Split out worker protocol template definitions from declarations
This is generally a fine practice: Putting implementations in headers
makes them harder to read and slows compilation. Unfortunately it is
necessary for templates, but we can ameliorate that by putting them in a
separate header. Only files which need to instantiate those templates
will need to include the header with the implementation; the rest can
just include the declaration.

This is now documenting in the contributing guide.

Also, it just happens that these polymorphic serializers are the
protocol agnostic ones. (Worker and serve protocol have the same logic
for these container types.) This means by doing this general template
cleanup, we are also getting a head start on better indicating which
code is protocol-specific and which code is shared between protocols.
2023-06-19 11:45:59 -04:00
John Ericson
c404623a1d
Clean up a few things related to profiles (#8526)
- Greatly expand API docs

- Clean up code in misc ways

  - Instead of a complicated single loop on generations, do different
    operations in successive subsequent steps.

  - Avoid `ref` in one place where `&` is fine

  - Just return path instead of mutating an argument in `makeName`

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
2023-06-19 04:04:59 +00:00
John Ericson
d2ce2e89b1 Split OptionalPathSetting from PathSetting
Rather than doing `allowEmpty` as boolean, have separate types and use
`std::optional`. This makes it harder to forget the possibility of an
empty path.

The `build-hook` setting was categorized as a `PathSetting`, but
actually it was split into arguments. No good! Now, it is
`Setting<Strings>` which actually reflects what it means and how it is
used.

Because of the subtyping, we now also have support for
`Setting<std::optional<String>>` in general. I imagine this can be used
to clean up many more settings also.
2023-06-18 23:31:18 -04:00
Eelco Dolstra
e503eadafc
Merge pull request #8477 from edolstra/tarball-flake-redirects
Tarball flake improvements
2023-06-16 18:03:50 +02:00
Valentin Gagarin
f695a74751
Update src/libstore/globals.hh 2023-06-16 17:58:01 +02:00
Valentin Gagarin
1a8ca85d48
use "store URLs" consistently 2023-06-16 14:34:11 +02:00
Eelco Dolstra
713836112c
Merge pull request #8517 from hercules-ci/fix-build-hook-error-for-lib-users
Fix build hook error for libstore library users
2023-06-16 13:20:50 +02:00
Valentin Gagarin
2ceacce484
Update src/libstore/globals.hh 2023-06-15 15:57:54 +02:00
Robert Hensing
d2696cdd1e Fix build hook error for libstore library users
A library shouldn't require changes to the caller's argument handling,
especially if it doesn't have to, and indeed we don't have to.

This changes the lookup order to prioritize the hardcoded path to nix
if it exists. The static executable still finds itself through /proc
and the like.
2023-06-15 14:32:00 +02:00
Valentin Gagarin
b7d47e1d22
fix wording 2023-06-15 04:58:07 +02:00
Valentin Gagarin
e09b40e0d0 reword documentation on trusted users and substituters
this is to make it slightly easier to scan over
2023-06-15 02:19:13 +02:00
Valentin Gagarin
a1cf16563f
Fixup description of substituters (#8291)
Introduce what substituters "are" in the configuration option entry.
Remove arbitrary line breaks for easier editing in the future.
Link glossary some more.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
Co-authored-by: John Ericson <git@JohnEricson.me>
2023-06-14 20:49:58 +00:00
John Ericson
61a3e1f2e2
Merge pull request #4282 from tweag/fix-ca-hash-rewriting
fix the hash rewriting for ca-derivations
2023-06-14 18:25:00 +02:00
Eelco Dolstra
1ad3328c5e Allow tarball URLs to redirect to a lockable immutable URL
Previously, for tarball flakes, we recorded the original URL of the
tarball flake, rather than the URL to which it ultimately
redirects. Thus, a flake URL like
http://example.org/patchelf-latest.tar that redirects to
http://example.org/patchelf-<revision>.tar was not really usable. We
couldn't record the redirected URL, because sites like GitHub redirect
to CDN URLs that we can't rely on to be stable.

So now we use the redirected URL only if the server returns the
`x-nix-is-immutable` or `x-amz-meta-nix-is-immutable` headers in its
response.
2023-06-13 14:17:45 +02:00
David McFarland
d5e1eb20a2 Pass common ssh options in isMasterRunning 2023-06-13 00:55:34 -03:00
Eelco Dolstra
87c66f6b0f Don't include uds-remote-store.md from a header file
Closes #8484.
2023-06-12 11:10:55 +02:00
Eelco Dolstra
381a32981b
Merge branch 'master' into angerman/mac-fix-recursive-nix 2023-06-09 13:06:47 +02:00
Eelco Dolstra
b56319a139
Merge pull request #8391 from aneeshusa/remove-wrong-default-value-in-docs-for-hashed-mirrors
Remove old default from docs for `hashed-mirrors`
2023-06-06 12:54:28 +02:00
Eelco Dolstra
864ab1a7ac
Merge pull request #8438 from zhaofengli/armv5tel-linux32
Also set the PER_LINUX32 personality flag on armv5tel-linux
2023-06-06 12:47:16 +02:00
Alexander Bantyev
a15b2c01c0
Document manual migration for use-xdg-base-directories (#8044)
* Document manual migration for use-xdg-base-directories

As there's currently no automatic migration for use-xdg-base-directories
option, add instructions for manual migration to the option's
description.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
2023-06-02 15:38:17 +00:00
Zhaofeng Li
48632e6139 Also set the PER_LINUX32 personality flag on armv5tel-linux 2023-06-02 03:04:13 -06:00
Eelco Dolstra
61ddfa154b
Merge pull request #8399 from tweag/fix-chrooted-stores-error-path
Properly report build errors on chrooted stores
2023-05-27 17:55:57 +02:00
Yorick van Pelt
2c462486fe
create pathAccessible, use it to infer default dirs 2023-05-26 15:36:47 +02:00
Yorick van Pelt
b7cde90c6b
Call getDefaultSSLCertFile() only when none is specified
This does pathExists on various paths, which crashes on EPERM in the
macOS sandbox.
2023-05-26 15:36:45 +02:00
Théophane Hufschmitt
d16a1994fb Properly report build errors on chrooted stores
When encountering a build error, Nix moves the output paths out of the
chroot into their final location (for “easier debugging of build
failures”). However this was broken for chroot stores as it was moving
it to the _logical_ location, not the _physical_ one.

Fix it by moving to the physical (_real_) location.

Fix https://github.com/NixOS/nix/issues/8395
2023-05-25 16:38:29 +02:00
Aneesh Agrawal
c694f1a2f3 Remove old default from docs for hashed-mirrors
The `hashed-mirrors` option did use to have this default value,
but it was removed and re-added with an empty default value.
As the autogenerated docs show the (actual) default values from code,
remove this incorrect reference from the docs.

I was updating my nix.conf settings after a few years and noticed this.
2023-05-24 11:05:40 -04:00
Théophane Hufschmitt
34e1b464f0 Normalize the hash-rewriting process when building derivations 2023-05-24 14:11:50 +02:00
Théophane Hufschmitt
a917fb0d53 Use a RewritingSink in derivation goal
Possibly this will make it stream
2023-05-24 14:11:50 +02:00
Théophane Hufschmitt
3ebe1341ab Make RewritingSink accept a map of rewrites
Giving it the same semantics as `rewriteStrings`.
Also add some tests for it
2023-05-24 14:11:50 +02:00
oxalica
303858afad Fix typo in error message of too long store path 2023-05-24 01:24:28 +08:00
Bernardo Meurer
bf693319f6
feat: add always-allow-substitutes
This adds a new configuration option to Nix, `always-allow-substitutes`,
whose effect is simple: it causes the `allowSubstitutes` attribute in
derivations to be ignored, and for substituters to always be used.

This is extremely valuable for users of Nix in CI, where usually
`nix-build-uncached` is used. There, derivations which disallow
substitutes cause headaches as the inputs for building already-cached
derivations need to be fetched to spuriously rebuild some simple text
file.

This option should be a good middle-ground, since it doesn't imply
rebuilding the world, such as the approach I took in
https://github.com/NixOS/nixpkgs/pull/221048
2023-05-22 19:42:29 +01:00
Théophane Hufschmitt
494a09c6df
Merge pull request #8377 from layus/fix-ssl-cert-mount
Make mounting ssl cert file optional
2023-05-22 14:06:57 +02:00
Théophane Hufschmitt
673fe85976
Merge pull request #8365 from obsidiansystems/proto-structs
Revert "Revert "Use template structs instead of phantoms""
2023-05-22 09:34:34 +02:00
Guillaume Maudoux
b14fea6fff Shortcircuit for empty caFile 2023-05-19 23:30:35 +02:00
Guillaume Maudoux
36b7e30c11 Make mounting ssl cert file optional 2023-05-19 22:47:40 +02:00
Eelco Dolstra
34381d5747
Merge pull request #8215 from obsidiansystems/general-repair-path
Support `repairPath` on most stores.
2023-05-19 13:39:48 +02:00
Eelco Dolstra
e31d9b910d
Merge pull request #7312 from layus/fixed-output-system-cert
Allow system certs access to fixed-output derivations
2023-05-19 13:05:16 +02:00
Robert Hensing
b1c34c0ee8
Merge pull request #8366 from obsidiansystems/worker-proto-forward-decl-types
Don't use `store-api.hh` in `worker-protocol.hh`
2023-05-18 14:33:52 +02:00
John Ericson
9923403d90 Don't use store-api.hh in worker-protocol.hh
Using abstract types like can help cut down on compilation time, both
from scratch, and especially incremental builds during development. The
idea is that `worker-protocol.hh` can declare all the (de)serializers, but
only again abstract types; when code needs to use some (de)serializers, it can
include headers just for the data types it needs to (de)serialize.

`store-api.hh` in particular is a bit of a sledgehammer, and the data
types we want to serialize have their own headers.
2023-05-18 00:20:24 -04:00
John Ericson
cb5052d98f Revert "Revert "Use template structs instead of phantoms""
This is the more typically way to do [Argument-dependent
lookup](https://en.cppreference.com/w/cpp/language/adl)-leveraging
generic serializers in C++. It makes the relationship between the `read`
and `write` methods more clear and rigorous, and also looks more
familiar to users coming from other languages that do not have C++'s
libertine ad-hoc overloading.

I am returning to this because during the review in
https://github.com/NixOS/nix/pull/6223, it came up as something that
would make the code easier to read --- easier today hopefully already,
but definitely easier if we were have multiple codified protocols with
code sharing between them as that PR seeks to accomplish.

If I recall correctly, the main criticism of this the first time around
(in 2020) was that having to specify the type when writing, e.g.
`WorkerProto<MyType>::write`, was too verbose and cumbersome. This is
now addressed with the `workerProtoWrite` wrapper function.

This method is also the way `nlohmann::json`, which we have used for a
number of years now, does its serializers, for what its worth.

This reverts commit 45a0ed82f0. That
commit in turn reverted 9ab07e99f5.
2023-05-17 22:44:47 -04:00
John Ericson
b9e5ce4a27 Upgrade downstreamPlaceholder to a type with methods
This gets us ready for dynamic derivation dependencies (part of RFC 92).
2023-05-17 17:41:16 -04:00
John Ericson
e7c1113a37 Add test for downstreamPlaceholder
This is good in general, but in particular ensures when we heavily
refactor it in the next commit there is less likelihood for an
unintentional change in behavior to sneak in.
2023-05-17 17:31:33 -04:00