astral-sh/uv

Individually specify enabled preview features in configuration

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#15767 opened on Sep 10, 2025

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 (1 comment) (2 reactions) (0 assignees)Rust (84,934 stars) (3,111 forks)batch import
configurationenhancementhelp wanted

Description

Summary

Currently, preview features can be enabled in two ways:

  • in configuration, with either the tool.uv.preview key in pyproject.toml or the preview key in uv.toml; or
  • on the command line, with the --preview-features or --preview flags, or the UV_PREVIEW or UV_PREVIEW_FEATURES environment variables.

There's a disparity here: On the command line, I have a choice between enabling all preview features (with --preview or UV_PREVIEW=1) and only enabling individual features (with --preview-features=foo,bar,baz or UV_PREVIEW_FEATURES=foo,bar,baz). However, in configuration, I only have the former choice, and no way to enable specific features individually.

It would be nice to have this granularity be available in configuration.

Example

A potential solution could be to change the type of the tool.uv.preview / preview value from a boolean to a list of strings:

# pyproject.toml
[tool.uv]
preview = [
  "json-output",
  "format"
]

Alternatively, to allow more flexibility when merging configs (plus backwards compatibility), we could use this format:

# pyproject.toml
[tool.uv]
preview = true

[tool.uv.preview-features]
json-output = true
format = true
pylock = false

In the latter case, setting tool.uv.preview-features.pylock = false would disable it, taking precedence over the feature potentially being enabled at a user level. If tool.uv.preview were changed to false, all preview features would be disabled, regardless of the content of tool.uv.preview-features.

Contributor guide

Tech stack
rustpython
Domain
backenddeveloper experiencetooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Rust programmingUnderstanding of config parsing
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Start by examining the current configuration parsing for preview features in the 'uv settings' or 'config' module. Look at how command line flags like ' preview features' and ' preview' are handled, and replicate that for TOML configuration. The PR should modify the schema for 'tool.uv.preview' to accept both boolean and list/map of strings, similar to the examples in the issue. Check for existing tests related to preview feature configuration to understand the expected behavior.