Take Tracks in TimelineBuilder::compile

[nixonyh]

Follows the builder no longer accumulating tracks itself. Tracks wraps a NonEmpty<Track>, so a timeline can't be built with zero tracks, and compile takes impl Into<Tracks> with a From<Track> impl so the single-track case stays b.compile(track).

Multiple tracks go through Tracks(nonempty![a, b]), with nonempty re-exported from motiongfx so callers don't depend on it directly.

CompileError::EmptyTimeline goes with it - the type now rules that case out, leaving the variant unconstructible.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 17009e68-5f31-4e2c-b176-5fefe92f9ba4

📥 Commits

Reviewing files that changed from the base of the PR and between 4db0f7b and dc312b2.

📒 Files selected for processing (5)

• crates/motiongfx/src/lib.rs
• crates/motiongfx/src/timeline.rs
• crates/motiongfx/src/track.rs
• examples/bevy_examples/examples/slide_basic.rs
• examples/vello_winit_example/examples/lissajous.rs

🚧 Files skipped from review as they are similar to previous changes (3)

• crates/motiongfx/src/lib.rs
• examples/vello_winit_example/examples/lissajous.rs
• examples/bevy_examples/examples/slide_basic.rs

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📝 Walkthrough

Summary by CodeRabbit

• New Features

  • Added support for compiling timelines from one or more tracks through a unified track collection.
  • Exposed track collection utilities through the public API and prelude.
  • Track collections now require at least one track.

• Refactor

  • Simplified timeline construction by removing separate track registration and empty-timeline handling.
  • Updated scene compilation, editor workflows, examples, benchmarks, and documentation to use the streamlined API.

Walkthrough

The PR adds a public non-empty TrackList, changes TimelineBuilder::compile to accept tracks directly, removes track accumulation and fallible empty compilation, updates scene error handling, and migrates repository call sites.

Changes

Timeline compilation API

Layer / File(s)	Summary
Tracks collection contract crates/motiongfx/src/track.rs, crates/motiongfx/src/lib.rs	Adds TrackList, collection helpers, boxed-slice conversion, and nonempty prelude exports.
TimelineBuilder compilation crates/motiongfx/src/timeline.rs	Changes compile to accept impl Into<TrackList>. Removes internal track storage, add_tracks, and try_compile.
Scene compilation and errors crates/motiongfx_scene/src/compile.rs, crates/motiongfx_scene/src/error.rs	Passes the root track directly to builder.compile and removes CompileError::EmptyTimeline.
Repository call-site migration crates/*/README.md, crates/motiongfx/benches/*, crates/motiongfx/docs/*, crates/motiongfx/examples/*, editor/motiongfx_editor/*, examples/bevy_examples/examples/*, examples/vello_winit_example/examples/*	Updates timeline construction to compile single tracks or explicitly ordered TrackList collections.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• voxell-tech/motiongfx#100: Updates related timeline compilation call sites.
• voxell-tech/motiongfx#103: Modifies related TimelineBuilder APIs.
• voxell-tech/motiongfx#124: Introduces related timeline compilation changes.

Suggested reviewers: jaghov

Poem

A rabbit builds a track list bright,
The builder compiles it right.
Examples follow the new API,
Ordered tracks hop by.
Empty timelines leave the run—
The migration is done!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 31.58% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main API change: passing tracks to TimelineBuilder::compile.
Description check	✅ Passed	The description explains the TrackList API, non-empty track enforcement, and removal of EmptyTimeline.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Create stacked PR
• Commit on current branch

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[Jaghov]

Looks good! Although the name Tracks is quite visually similar to track. Maybe TrackList might be better, or just a more distinct name.