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Merge remote-tracking branch 'upstream/master' into list-experimental-features

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John Ericson 2023-04-06 18:07:46 -04:00
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1
doc/manual/src/SUMMARY.md.in
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@ -95,6 +95,7 @@
- [Glossary](glossary.md)
- [Contributing](contributing/contributing.md)
- [Hacking](contributing/hacking.md)
- [Experimental Features](contributing/experimental-features.md)
- [CLI guideline](contributing/cli-guideline.md)
- [Release Notes](release-notes/release-notes.md)
- [Release X.Y (202?-??-??)](release-notes/rl-next.md)

3
doc/manual/src/command-ref/nix-shell.md
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@ -120,7 +120,8 @@ shell in which to build it:
```console
$ nix-shell '<nixpkgs>' -A pan
[nix-shell]$ eval ${unpackPhase:-unpackPhase}
[nix-shell]$ cd pan-*
[nix-shell]$ cd $sourceRoot
[nix-shell]$ eval ${patchPhase:-patchPhase}
[nix-shell]$ eval ${configurePhase:-configurePhase}
[nix-shell]$ eval ${buildPhase:-buildPhase}
[nix-shell]$ ./pan/gui/pan

91
doc/manual/src/contributing/experimental-features.md Normal file
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@ -0,0 +1,91 @@
This section describes the notion of *experimental features*, and how it fits into the big picture of the development of Nix.
# What are experimental features?
Experimental features are considered unstable, which means that they can be changed or removed at any time.
Users must explicitly enable them by toggling the associated [experimental feature flags](@docroot@/command-ref/conf-file.md#conf-experimental-features).
This allows accessing unstable functionality without unwittingly relying on it.
Experimental feature flags were first introduced in [Nix 2.4](@docroot@/release-notes/rl-2.4.md).
Before that, Nix did have experimental features, but they were not guarded by flags and were merely documented as unstable.
This was a source of confusion and controversy.
# When should a new feature be marked experimental?
A change in the Nix codebase should be guarded by an experimental feature flag if it is considered likely to be reverted or adapted in a backwards-incompatible manner after gathering more experience with it in practice.
Examples:
- Changes to the Nix language, such as new built-ins, syntactic or semantic changes, etc.
- Changes to the command-line interface
# Lifecycle of an experimental feature
Experimental features have to be treated on a case-by-case basis.
However, the standard workflow for an experimental feature is as follows:
- A new feature is implemented in a *pull request*
- It is guarded by an experimental feature flag that is disabled by default
- The pull request is merged, the *experimental* feature ends up in a release
- Using the feature requires explicitly enabling it, signifying awareness of the potential risks
- Being experimental, the feature can still be changed arbitrarily
- The feature can be *removed*
- The associated experimental feature flag is also removed
- The feature can be declared *stable*
- The associated experimental feature flag is removed
- There should be enough evidence of users having tried the feature, such as feedback, fixed bugs, demonstrations of how it is put to use
- Maintainers must feel confident that:
- The feature is designed and implemented sensibly, that it is fit for purpose
- Potential interactions are well-understood
- Stabilising the feature will not incur an outsized maintenance burden in the future
The following diagram illustrates the process:
```
.------.
| idea |
'------'
|
discussion, design, implementation
|
| .-------.
| | |
v v |
.--------------. review
| pull request | |
'--------------' |
| ^ | |
| | '-------'
.---' '----.
| |
merge user feedback,
| (breaking) changes
| |
'---. .----'
| |
v |
+--------------+
.---| experimental |----.
| +--------------+ |
| |
decision to stabilise decision against
| keeping the feature
| |
v v
+--------+ +---------+
| stable | | removed |
+--------+ +---------+
```
# Relation to the RFC process
Experimental features and [RFCs](https://github.com/NixOS/rfcs/) both allow approaching substantial changes while minimizing the risk.
However they serve different purposes:
- An experimental feature enables developers to iterate on and deliver a new idea without committing to it or requiring a costly long-running fork.
It is primarily an issue of *implementation*, targeting Nix developers and early testers.
- The goal of an RFC is to make explicit all the implications of a change:
Explain why it is wanted, which new use-cases it enables, which interface changes it requires, etc.
It is primarily an issue of *design* and *communication*, targeting the broader community.
This means that experimental features and RFCs are orthogonal mechanisms, and can be used independently or together as needed.

26
doc/manual/src/glossary.md
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@ -54,7 +54,7 @@
invoked, the Nix store can be referred to
as a "_local_" or a "_remote_" one:
+ A *local store* exists on the filesystem of
+ A [local store]{#gloss-local-store} exists on the filesystem of
the machine where Nix is invoked. You can use other
local stores by passing the `--store` flag to the
`nix` command. Local stores can be used for building derivations.
@ -65,17 +65,17 @@
served by the `nix-serve` Perl script.
[store]: #gloss-store
[local store]: #gloss-local-store
- [chroot store]{#gloss-chroot-store}\
A local store whose canonical path is anything other than `/nix/store`.
A [local store] whose canonical path is anything other than `/nix/store`.
- [binary cache]{#gloss-binary-cache}\
A *binary cache* is a Nix store which uses a different format: its
metadata and signatures are kept in `.narinfo` files rather than in a
Nix database. This different format simplifies serving store objects
over the network, but cannot host builds. Examples of binary caches
include S3 buckets and the [NixOS binary
cache](https://cache.nixos.org).
[Nix database]. This different format simplifies serving store objects
over the network, but cannot host builds. Examples of binary caches
include S3 buckets and the [NixOS binary cache](https://cache.nixos.org).
- [store path]{#gloss-store-path}\
The location of a [store object] in the file system, i.e., an
@ -108,7 +108,7 @@
[fixed-output derivations](#gloss-fixed-output-derivation).
- [substitute]{#gloss-substitute}\
A substitute is a command invocation stored in the Nix database that
A substitute is a command invocation stored in the [Nix database] that
describes how to build a store object, bypassing the normal build
mechanism (i.e., derivations). Typically, the substitute builds the
store object by downloading a pre-built version of the store object
@ -127,6 +127,14 @@
builder can rely on external inputs such as the network or the
system time) but the Nix model assumes it.
- Nix database{#gloss-nix-database}\
An SQlite database to track [reference]s between [store object]s.
This is an implementation detail of the [local store].
Default location: `/nix/var/nix/db`.
[Nix database]: #gloss-nix-database
- [Nix expression]{#gloss-nix-expression}\
A high-level description of software packages and compositions
thereof. Deploying software using Nix entails writing Nix
@ -175,9 +183,9 @@
- [validity]{#gloss-validity}\
A store path is valid if all [store object]s in its [closure] can be read from the [store].
For a local store, this means:
For a [local store], this means:
- The store path leads to an existing [store object] in that [store].
- The store path is listed in the Nix database as being valid.
- The store path is listed in the [Nix database] as being valid.
- All paths in the store path's [closure] are valid.
[validity]: #gloss-validity

5
maintainers/README.md
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@ -56,7 +56,7 @@ Meeting notes are collected on a [collaborative scratchpad](https://pad.lassul.u
The team uses a [GitHub project board](https://github.com/orgs/NixOS/projects/19/views/1) for tracking its work.
Issues on the board progress through the following states:
Items on the board progress through the following states:
- No Status
@ -80,6 +80,9 @@ Issues on the board progress through the following states:
If there is disagreement on the general idea behind an issue or pull request, it is moved to _To discuss_, otherwise to _In review_.
To ensure process quality and reliability, all non-trivial pull requests must be triaged before merging.
What constitutes a trivial pull request is up to maintainers' judgement.
- To discuss
Pull requests and issues that are deemed important and controversial are discussed by the team during discussion meetings.