mirror of
https://github.com/privatevoid-net/nix-super.git
synced 2024-11-24 14:56:15 +02:00
eb7d7780b1
This is needed to avoid this https://github.com/mesonbuild/meson/issues/13774 when we go back to making our subproject directory `src`.
95 lines
4.4 KiB
Markdown
95 lines
4.4 KiB
Markdown
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.
|
|
|
|
# Currently available experimental features
|
|
|
|
{{#include ./experimental-feature-descriptions.md}}
|