compose-expert（作曲专家）

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Compose Expert Skill

Non-opinionated, practical guidance for writing correct, performant Compose code — across Android, Desktop, iOS, and Web. Covers Jetpack Compose and Compose Multiplatform. Backed by analysis of actual source code from androidx/androidx and JetBrains/compose-multiplatform-core.

Review Mode

Activate when the input contains a GitHub PR URL (github.com/.+/pull/\d+) or explicit review phrases: "review this PR", "review this diff", "check this code", "what's wrong with this".

When Review Mode activates:

1. Do not follow the generation workflow below
2. Read references/pr-review.md and follow its workflow exclusively
3. Output a structured local review report — do not post to GitHub

Workflow

When helping with Compose code, follow this checklist:

1. Understand the request

• What Compose layer is involved? (Runtime, UI, Foundation, Material3, Navigation)
• Is this a state problem, layout problem, performance problem, or architecture question?
• Is this Android-only or Compose Multiplatform (CMP)?

2. Analyze the design (if visual reference provided)

• If the user shares a Figma frame, screenshot, or design spec, consult references/design-to-compose.md
• Decompose the design into a composable tree using the 5-step methodology
• Map design tokens to MaterialTheme, spacing to CompositionLocals
• Identify animation needs and consult references/animation.md for recipes

3. Consult the right reference

Read the relevant reference file(s) from references/ before answering:

4. Apply and verify

• Write code that follows the patterns in the reference
• Flag any anti-patterns you see in the user's existing code
• Suggest the minimal correct solution — don't over-engineer

4a. Component building mode

When the request involves building a component (composable that renders UI):

• Consult references/atomic-design.md
• Classify the component level (atom, molecule, organism, template)
• Apply the "Ask" prompt from Section 5 before scaffolding code
• Ensure the component satisfies the atom contract (modifier, slots, tokens, defaults)

5. Cite the source

When referencing Compose internals, point to the exact source file:

// See: compose/runtime/runtime/src/commonMain/kotlin/androidx/compose/runtime/Composer.kt

Key Principles

1. Compose thinks in three phases: Composition → Layout → Drawing. State reads in each phase only trigger work for that phase and later ones.
2. Recomposition is frequent and cheap — but only if you help the compiler skip unchanged scopes. Use stable types, avoid allocations in composable bodies.
3. Modifier order matters. Modifier.padding(16.dp).background(Color.Red) is visually different from Modifier.background(Color.Red).padding(16.dp).
4. State should live as low as possible and be hoisted only as high as needed. Don't put everything in a ViewModel just because you can.
5. Side effects exist to bridge Compose's declarative world with imperative APIs. Use the right one for the job — misusing them causes bugs that are hard to trace.
6. Compose Multiplatform shares the runtime but not the platform. UI code in commonMain is portable. Platform-specific APIs (LocalContext, BackHandler, Window) require expect/actual or conditional source sets.

Source Code Receipts

Beyond the guidance docs, this skill bundles the actual source code from androidx/androidx (branch: androidx-main) and JetBrains/compose-multiplatform-core (branch: jb-main). When you need to verify how something works internally, or the user asks "show me the actual implementation", read the raw source from references/source-code/:

Two-layer approach

1. Start with guidance — read the topic-specific reference (e.g., references/state-management.md)
2. Go deeper with source — if the user wants receipts or you need to verify, read from references/source-code/

Source tree map

androidx/androidx (branch: androidx-main)
├── compose/runtime/runtime/src/commonMain/kotlin/androidx/compose/runtime/
├── compose/ui/ui/src/androidMain/kotlin/androidx/compose/ui/platform/
├── compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/
├── compose/foundation/foundation/src/commonMain/kotlin/androidx/compose/foundation/
├── compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/
├── compose/navigation/navigation-compose/src/commonMain/kotlin/androidx/navigation/compose/
├── tv/tv-material/src/main/java/androidx/tv/material3/
└── tv/tv-foundation/src/main/java/androidx/tv/foundation/

compose-multiplatform-core (branch: jb-main)
├── compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/window/
├── compose/ui/ui/src/iosMain/kotlin/androidx/compose/ui/window/
├── compose/ui/ui/src/webMain/kotlin/androidx/compose/ui/window/
├── compose/ui/ui/src/skikoMain/kotlin/androidx/compose/ui/
└── compose/foundation/foundation/src/skikoMain/kotlin/androidx/compose/foundation/

compose-multiplatform (resources library)
└── components/resources/library/src/commonMain/