Cargo Feature Collections #21472

cart · 2025-10-08T22:40:59Z

Objective

Users of the bevy crate currently live one of two lifestyles:

Use all of Bevy's default features, potentially compiling many features you don't need or don't want. If there is a feature you cannot have in your app, you must move on to option (2)
Disable Bevy's default features, and compose the complete list of features yourself.

Living in the world of (2) is an exercise in frustration, as the list of required features to accomplish a given task changes regularly across releases as we add and change features. This is an expert level task that requires intimate knowledge of engine internals to get right. Even I, Bevy's lead developer, would struggle here. To the point that I would never voluntarily choose to disable Bevy's default features.

Most games/apps are 2D-only, 3D-only, or UI-only and don't require the full set of features. We cannot currently in good conscience recommend that those developers live in the "no default features" world. That is a fast track to pain, suffering, and perhaps a quick exit from the Bevy ecosystem.

The same problem exists for developers that want to build their own Bevy renderer or replace Bevy UI with their own framework. Once again, we cannot recommend that those developers manage every Bevy feature themselves.

Fixes: #21369
Alternative to: #20741 #21236

Solution

Define a "standalone" set of features that enable Bevy developers to disable default features, then opt in to the funtionality they want. The "default" bevy feature set is now just:

default = ["2d", "3d", "ui"]

This enables developers to select only the features they need. For example, a UI-only app would look like this:

bevy = { version = "0.17", default-features = false, features = [ "ui" ] }

"2d", "3d", and "ui" each contain the "full" Bevy experience for that domain. This also includes:

default_platform: the default "platform support" features (see docs)
default_app: the default "app framework" features (see docs)

For developers that do not want the default bevy render / platform / app functionality, this breaks down further into:

common_api: common / core backend-less user-facing Bevy render api
2d_api: common / core backend-less user-facing Bevy 2d api
3d_api: common / core backend-less user-facing Bevy 3d api
ui_api: common / core backend-less user-facing Bevy ui api

(and many others)

I've also added the dev feature to this PR, which enables the recommended "dev only" features like dynamic linking, asset watching / hot reloading, and dev / debug tools. Including dynamic linking is a bit controversial here given that it doesn't work everywhere. But I'd like to aggressively push people into the dynamic linking workflow wherever possible, as developing without it is signficantly worse. And removing a single dev feature is a much simpler release workflow.

github-actions · 2025-10-08T22:41:13Z

It looks like your PR has been selected for a highlight in the next release blog post, but you didn't provide a release note.

Please review the instructions for writing release notes, then expand or revise the content in the release notes directory to showcase your changes.

atlv24

Thank you!

Cargo.toml

atlv24 · 2025-10-08T23:10:17Z

The feature generation tool will almost definitely not be able to cope with this, i noticed some weird edge cases a while back. Its going to need to be updated to display something meaningful for this

github-actions · 2025-10-08T23:14:09Z

You added a new feature but didn't update the readme. Please run cargo run -p build-templated-pages -- update features to update it, and commit the file change.

PROMETHIA-27

Could there be a headless configuration? Is that just default_app? My current usecase is a headless server.

Cargo.toml

github-actions · 2025-10-09T00:07:48Z

It looks like your PR is a breaking change, but you didn't provide a migration guide.

Please review the instructions for writing migration guides, then expand or revise the content in the migration guides directory to reflect your changes.

…atures

…re. Move "default_app" to "complete" profiles.

atlv24

I think the toml docs heavily overuse "scare quotes" (try reading it without them, it flows better imo) but this is good to merge from a purely technical perspective

Cargo.toml

atlv24 · 2025-10-09T22:21:41Z

Cargo.toml

+]
+
+# Features used to build UI Bevy apps (this includes the bevy_render backend).
+# Add this to your app if you would like the "default" Bevy UI experience.


Suggested change

# Add this to your app if you would like the "default" Bevy UI experience.

# Add this to your app if you would like the default Bevy UI experience.

Cargo.toml

Co-authored-by: atlv <[email protected]>

cart · 2025-10-10T01:52:13Z

Ok this should be good to go. I've updated our cargo_features.md tooling to handle the concept of "feature profiles" and "feature collections" (take a look at the new generated cargo_features.md). Cargo features can opt-in to this designation with a COLLECTION: or PROFILE: prefix in their documentation.

This removes the "default" vs "non-default" feature presentation strategy. I consider that approach to be broken in its current form, as it doesn't accommodate the idea that features can contain other features (I believe that resulted in incorrect results before this PR). We can re-add that distinction if that is handled. But for now, I've switched to a sorted list of non-profile, non-collection cargo features.

atlv24 · 2025-10-10T02:22:06Z

Cargo.toml

+audio = ["bevy_audio", "vorbis"]
+
+# COLLECTION: Features used to compose Bevy scenes.
+scene = ["bevy_scene"]


Will this collection ever have any other entry? Why not just use bevy_scene?

Actually, will bsn go here? bevy_bsn?

There is a high likelihood that the next generation scene system will be broken up into bevy_scene (everything but the bsn asset / macro) and bevy_bsn (bsn asset and macro).

atlv24

LGTM

## Objective Users of the `bevy` crate currently live one of two lifestyles: 1. Use all of Bevy's default features, potentially compiling many features you don't need or don't want. If there is a feature you _cannot have_ in your app, you must move on to option (2) 2. Disable Bevy's default features, and compose the complete list of features yourself. Living in the world of (2) is an exercise in frustration, as the list of required features to accomplish a given task changes regularly across releases as we add and change features. This is an _expert level_ task that requires intimate knowledge of engine internals to get right. Even I, Bevy's lead developer, would struggle here. To the point that I would never voluntarily choose to disable Bevy's default features. Most games/apps are 2D-only, 3D-only, or UI-only and don't require the full set of features. We cannot currently in good conscience recommend that those developers live in the "no default features" world. That is a fast track to pain, suffering, and perhaps a quick exit from the Bevy ecosystem. The same problem exists for developers that want to build their own Bevy renderer or replace Bevy UI with their own framework. Once again, we _cannot_ recommend that those developers manage every Bevy feature themselves. Fixes: bevyengine#21369 Alternative to: bevyengine#20741 bevyengine#21236 ## Solution Define a "standalone" set of features that enable Bevy developers to disable default features, then opt in to the funtionality they want. The "default" `bevy` feature set is now just: ```toml default = ["2d", "3d", "ui"] ``` This enables developers to select only the features they need. For example, a UI-only app would look like this: ```toml bevy = { version = "0.17", default-features = false, features = [ "ui" ] } ``` "2d", "3d", and "ui" each contain the "full" Bevy experience for that domain. This also includes: - `default_platform`: the default "platform support" features (see docs) - `default_app`: the default "app framework" features (see docs) For developers that do not want the default bevy render / platform / app functionality, this breaks down further into: - `common_api`: common / core backend-less user-facing Bevy render api - `2d_api`: common / core backend-less user-facing Bevy 2d api - `3d_api`: common / core backend-less user-facing Bevy 3d api - `ui_api`: common / core backend-less user-facing Bevy ui api (and many others) I've also added the `dev` feature to this PR, which enables the recommended "dev only" features like dynamic linking, asset watching / hot reloading, and dev / debug tools. Including dynamic linking is a bit controversial here given that it doesn't work everywhere. But I'd like to aggressively push people into the dynamic linking workflow wherever possible, as developing without it is signficantly worse. And removing a single `dev` feature is a much simpler release workflow. --------- Co-authored-by: atlv <[email protected]>

Cargo Feature Collections

edebd11

cart added this to the 0.18 milestone Oct 8, 2025

cart added A-Build-System Related to build systems or continuous integration C-Usability A targeted quality-of-life change that makes Bevy easier to use A-App Bevy apps and plugins M-Release-Note Work that should be called out in the blog due to impact labels Oct 8, 2025

This was referenced Oct 8, 2025

Add default_no_render #20741

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enable bevy_dev_tools by default #21236

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alice-i-cecile added X-Blessed Has a large architectural impact or tradeoffs, but the design has been endorsed by decision makers S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Oct 8, 2025

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Contributor guide for feature flag usage #20867

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ECS debug names should be on by default #21478

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cart added 4 commits October 9, 2025 13:07

Address comments

81904a1

Make 2d/3d/ui "complete" feature packages. Split out x_bevy_render fe…

aebe020

…atures

Make 2d/3d/ui "complete" feature profiles. High level "picking" featu…

baa2ba8

…re. Move "default_app" to "complete" profiles.

Release notes

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cart and others added 7 commits October 9, 2025 17:14

Apply suggestions from code review

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Co-authored-by: atlv <[email protected]>

render_api -> common_api

5936f9a

Add migration guide

f1ec4d7

lint

352f9e1

Make compatible with current cargo_features.md

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Update cargo_features.md tooling to handle "profiles" and "collections"

451249e

Filter out profiles and collections

1c34c4e

cart added 3 commits October 9, 2025 18:53

Update description

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Remove double newlines in generated file

a0de161

Use "group" instead of "collection" to avoid confusion in a few places

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atlv24 added S-Needs-Review Needs reviewer attention (from anyone!) to move forward and removed S-Waiting-on-Author The author needs to make changes or address concerns before this can be merged labels Oct 10, 2025

alice-i-cecile added S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it and removed S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Oct 10, 2025

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Merged via the queue into main with commit f3ec3c0 Oct 10, 2025
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tychedelia mentioned this pull request Oct 16, 2025

libprocessing ffi error handling processing/processing4#1293

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	# Add this to your app if you would like the "default" Bevy UI experience.
	# Add this to your app if you would like the default Bevy UI experience.

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Cargo Feature Collections #21472

Cargo Feature Collections #21472

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