Find a file
John Ericson 85f0cdc370 Use std::set<StringContextElem> not PathSet for string contexts
Motivation

`PathSet` is not correct because string contexts have other forms
(`Built` and `DrvDeep`) that are not rendered as plain store paths.
Instead of wrongly using `PathSet`, or "stringly typed" using
`StringSet`, use `std::std<StringContextElem>`.

-----

In support of this change, `NixStringContext` is now defined as
`std::std<StringContextElem>` not `std:vector<StringContextElem>`. The
old definition was just used by a `getContext` method which was only
used by the eval cache. It can be deleted altogether since the types are
now unified and the preexisting `copyContext` function already suffices.

Summarizing the previous paragraph:

Old:

  - `value/context.hh`: `NixStringContext = std::vector<StringContextElem>`
  - `value.hh`: `NixStringContext Value::getContext(...)`
  - `value.hh`: `copyContext(...)`

New:

  - `value/context.hh`: `NixStringContext = std::set<StringContextElem>`
  - `value.hh`: `copyContext(...)`
----

The string representation of string context elements no longer contains
the store dir. The diff of `src/libexpr/tests/value/context.cc` should
make clear what the new representation is, so we recommend reviewing
that file first. This was done for two reasons:

Less API churn:

`Value::mkString` and friends did not take a `Store` before. But if
`NixStringContextElem::{parse, to_string}` *do* take a store (as they
did before), then we cannot have the `Value` functions use them (in
order to work with the fully-structured `NixStringContext`) without
adding that argument.

That would have been a lot of churn of threading the store, and this
diff is already large enough, so the easier and less invasive thing to
do was simply make the element `parse` and `to_string` functions not
take the `Store` reference, and the easiest way to do that was to simply
drop the store dir.

Space usage:

Dropping the `/nix/store/` (or similar) from the internal representation
will safe space in the heap of the Nix programming being interpreted. If
the heap contains many strings with non-trivial contexts, the saving
could add up to something significant.

----

The eval cache version is bumped.

The eval cache serialization uses `NixStringContextElem::{parse,
to_string}`, and since those functions are changed per the above, that
means the on-disk representation is also changed.

This is simply done by changing the name of the used for the eval cache
from `eval-cache-v4` to eval-cache-v5`.

----

To avoid some duplication `EvalCache::mkPathString` is added to abstract
over the simple case of turning a store path to a string with just that
string in the context.

Context

This PR picks up where #7543 left off. That one introduced the fully
structured `NixStringContextElem` data type, but kept `PathSet context`
as an awkward middle ground between internal `char[][]` interpreter heap
string contexts and `NixStringContext` fully parsed string contexts.

The infelicity of `PathSet context` was specifically called out during
Nix team group review, but it was agreeing that fixing it could be left
as future work. This is that future work.

A possible follow-up step would be to get rid of the `char[][]`
evaluator heap representation, too, but it is not yet clear how to do
that. To use `NixStringContextElem` there we would need to get the STL
containers to GC pointers in the GC build, and I am not sure how to do
that.

----

PR #7543 effectively is writing the inverse of a `mkPathString`,
`mkOutputString`, and one more such function for the `DrvDeep` case. I
would like that PR to have property tests ensuring it is actually the
inverse as expected.

This PR sets things up nicely so that reworking that PR to be in that
more elegant and better tested way is possible.

Co-authored-by: Théophane Hufschmitt <7226587+thufschmitt@users.noreply.github.com>
2023-04-21 01:05:49 -04:00
.github Merge pull request #8153 from obsidiansystems/more-labeler 2023-04-11 12:10:34 +02:00
config Run autoupdate 2021-06-01 11:42:38 +02:00
contrib function-trace: always show the trace 2019-09-18 23:23:21 +02:00
doc Update installing-binary.md 2023-04-18 13:18:30 +03:00
m4 autoconf: Fix C++17 detection not working on Ubuntu 16.04. 2019-07-03 04:32:25 +02:00
maintainers Merge pull request #7579 from fricklerhandwerk/review-process 2023-04-05 01:57:17 +02:00
misc Add a setting for configuring the SSL certificates file 2023-03-17 18:32:18 +01:00
mk Enable -Werror=switch-enum 2023-04-03 18:45:20 +02:00
perl Merge pull request #3746 from obsidiansystems/path-info 2023-04-17 15:49:48 +02:00
scripts Merge pull request #7925 from cole-h/fixup-xdg-nix-env 2023-03-01 23:01:42 +01:00
src Use std::set<StringContextElem> not PathSet for string contexts 2023-04-21 01:05:49 -04:00
tests Move test/recursive.sh nix expr to file 2023-04-19 19:36:05 -04:00
.dir-locals.el .dir-locals.el: Set c-block-comment-prefix 2020-07-10 11:21:06 +02:00
.editorconfig Add .editorconfig 2017-06-05 22:57:28 +01:00
.gitignore Single page for experimental feature descriptions 2023-04-09 11:01:23 -04:00
.version Bump version 2023-04-11 20:16:37 +02:00
boehmgc-coroutine-sp-fallback.diff Always disable GC in a coroutine unless the patch is applied 2023-04-07 14:54:38 +02:00
bootstrap.sh bootstrap: Simplify & make more robust. 2011-09-06 12:11:05 +00:00
configure.ac Merge pull request #7732 from hercules-ci/make-initLibStore-viable-alternative 2023-04-17 08:04:41 -04:00
CONTRIBUTING.md Add CONTRIBUTING.md 2023-03-11 22:14:14 +01:00
COPYING * Change this to LGPL to keep the government happy. 2006-04-25 16:41:06 +00:00
default.nix add flake-compat to flake.nix and use sha256 in default.nix 2023-03-06 21:11:24 +01:00
docker.nix docker.nix: add an option to include flake-registry inside docker image (#6750) 2023-03-22 20:55:02 +01:00
flake.lock add flake-compat to flake.nix and use sha256 in default.nix 2023-03-06 21:11:24 +01:00
flake.nix fix failing configure in nix-tests 2023-04-09 02:33:53 +02:00
local.mk Enable -Werror=switch-enum 2023-04-03 18:45:20 +02:00
Makefile Generate API docs with Doxygen 2023-03-10 12:51:06 -05:00
Makefile.config.in Generate API docs with Doxygen 2023-03-10 12:51:06 -05:00
precompiled-headers.h Config: Use nlohmann/json 2020-08-20 11:02:16 +02:00
README.md Improve hacking.md 2023-02-13 12:00:00 +04:00
shell.nix Remove url literals 2022-01-24 13:28:21 +01:00

Nix

Open Collective supporters Test

Nix is a powerful package manager for Linux and other Unix systems that makes package management reliable and reproducible. Please refer to the Nix manual for more details.

Installation

On Linux and macOS the easiest way to install Nix is to run the following shell command (as a user other than root):

$ curl -L https://nixos.org/nix/install | sh

Information on additional installation methods is available on the Nix download page.

Building And Developing

See our Hacking guide in our manual for instruction on how to to set up a development environment and build Nix from source.

Additional Resources

License

Nix is released under the LGPL v2.1.