review-unity-specific

name

review-unity-specific

description

Detection-only checklist for Unity-specific gotchas that no static analyzer catches — Prefab Variant YAML traps, ARFoundation lifecycle ordering, XR plugin switching, asmdef versionDefines, UI Toolkit overflow, .meta safety, and Unity Hub module paths. Runs a grep/find detection command per trap and reports ✓/✗ with affected files. Does NOT fix anything, and does NOT evaluate metrics or architecture (review-metrics / review-architecture).

Unity Review — Unity-Specific Gotchas

This skill is detection only. Each item below is a known trap that compiles clean, passes unilyze, and still breaks at build time, on device, or across a domain reload. Run the detection command, decide ✓ (safe / not present) or ✗ (trap present), and list affected files. You do not fix; you surface.

Run review-triage first for the project profile — the XR items only apply if triage recorded an XR stack.

For each trap: Symptom (what the developer sees), Cause (the underlying mechanism), Detect (the command to run), Severity.

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1. Prefab Variant m_AddedComponents with implicit fileIDs

• Symptom: components added on a Prefab Variant silently vanish in builds or when the base prefab is restructured.
• Cause: a variant records added components as overrides keyed by the base prefab's serialized fileID. If the base prefab is edited so those fileIDs shift, the override dangles and Unity drops the component with no error.
• Detect: grep -rln "m_AddedComponents\|m_RemovedComponents" <project>/Assets --include=*.prefab then open each and confirm no override references a stripped/missing fileID.
• Severity: high (silent build-time loss).

2. ARFoundation SubsystemLifecycleManager AddComponent ordering

• Symptom: an AR manager added at runtime (e.g. ARPlaneManager) never activates; its subsystem stays stopped.
• Cause: managers derived from SubsystemLifecycleManager bind to their subsystem in OnEnable. gameObject.AddComponent<ARPlaneManager>() after the ARSession is already running, or on a disabled GameObject, adds it in a state where the subsystem was never started. Order matters: session/config first, then managers, on an enabled object.
• Detect: grep -rn "AddComponent<AR\|AddComponent<XR" <project>/Assets --include=*.cs
• Severity: high on xr-app, otherwise n/a.

3. XREAL Image Tracking vs Marker Tracking confusion

• Symptom: tracking configured but nothing is detected on device.
• Cause: the XREAL SDK exposes Image Tracking and Marker Tracking as distinct subsystems with separate config assets. Wiring the tracked-image database into a marker-tracking flow (or vice versa) compiles fine and tracks nothing.
• Detect: grep -rn "NRTrackableImage\|TrackingImageDatabase\|MarkerTracking\|NRMarker" <project>/Assets --include=*.cs and confirm the config asset matches the subsystem in use.
• Severity: medium on xr-app, otherwise n/a.

4. Gradle TLS handshake failure

• Symptom: Android build fails resolving dependencies with a TLS/SSL handshake error.
• Cause: gradle.properties (or the JDK's jdk.tls.disabledAlgorithms) restricts TLS versions, and a repository requires a version that was disabled. Common after a Unity/JDK upgrade.
• Detect: find <project> -name "gradle.properties" -exec grep -Hn "tls\|https.protocols\|systemProp" {} + and check for a restrictive TLS setting.
• Severity: high (Android build blocker).

5. SessionState vs EditorPrefs for cross-recompile state

• Symptom: editor-tool state is lost after a script recompile, or unexpectedly persists across Editor restarts.
• Cause: EditorPrefs persists indefinitely (registry/plist) — wrong for transient state, which then leaks between sessions. SessionState persists only within one Editor session, surviving domain reloads but cleared on exit — the correct store for "remember across recompile, forget on restart."
• Detect: grep -rn "EditorPrefs.Set\|SessionState.Set" <project>/Assets --include=*.cs (paths under /Editor/), then judge whether the chosen store matches the intended lifetime.
• Severity: medium (state bugs in tooling).

6. asmdef versionDefines not set for optional SDK dependencies

• Symptom: code guarded by #if SOME_SDK never compiles even when the SDK is installed, or the assembly fails to compile when the SDK is absent.
• Cause: the #if symbol must be produced by the asmdef's versionDefines (define this symbol when package X ≥ version Y is present). Without it, the symbol is never defined and the guarded code silently drops out — or hard-references break when the optional package is missing.
• Detect: grep -rn "#if " <project>/Assets --include=*.cs | grep -iv "UNITY_\|DEBUG\|UNITY_EDITOR" to find SDK guards, then grep -rln "versionDefines" <project>/Assets --include=*.asmdef and confirm each guard symbol is defined.
• Severity: medium.

7. UI Toolkit text-overflow requires 3 properties + a width constraint

• Symptom: long text is not truncated with an ellipsis; it overflows or wraps unexpectedly.
• Cause: UI Toolkit ellipsis needs all of text-overflow: ellipsis, overflow: hidden, and white-space: nowrap, plus a bounded element width. Any one missing and truncation silently does not apply.
• Detect: grep -rn "text-overflow\|white-space\|overflow" <project>/Assets --include=*.uss and cross-check each truncating label has all three plus a width.
• Severity: low (UI polish).

8. .meta file hand-editing

• Symptom: broken asset references, reimport churn, or GUID collisions after a commit.
• Cause: a .meta file binds an asset path to its GUID and import settings. Hand-editing it (especially the guid:) desyncs every reference that points at the old GUID. Meta files must change only through the Editor.
• Detect: git -C <project> log --oneline -5 -- '*.meta' and git -C <project> diff --stat -- '*.meta' — flag any hand edit to a guid: line.
• Severity: high. If a .meta or YAML asset genuinely needs a scripted change, route it through the unity-yaml-editing-guide skill — never a freehand edit.

9. XRLoader switching via XRPackageMetadataStore (needs reflection for featureId)

• Symptom: programmatic XR loader / plugin-provider switching (e.g. build automation toggling OpenXR features) fails silently or throws.
• Cause: XRPackageMetadataStore and the featureId accessors used to enable/disable OpenXR features are internal API; correct access requires reflection, and the surface changes between XR Management versions.
• Detect: grep -rn "XRPackageMetadataStore\|XRGeneralSettings\|OpenXRSettings\|SetFeatureEnabled" <project>/Assets --include=*.cs
• Severity: medium on xr-app, otherwise n/a.

10. Unity Hub module (PlaybackEngines) path assumptions

• Symptom: a build script reports a build-target module (Android/iOS/etc.) as not installed even though it is.
• Cause: PlaybackEngines live in different places depending on install method. On macOS a Hub-installed editor keeps them under Hub/Editor/{VERSION}/PlaybackEngines, while a standalone/manually placed editor uses <Unity>.app/Contents/PlaybackEngines. A script hard-coding one path misses the other.
• Detect: grep -rn "PlaybackEngines\|Contents/PlaybackEngines\|Hub/Editor" <project> --include=*.cs --include=*.sh --include=*.yml
• Severity: medium (CI / build-tooling breakage).

11. Deprecated FindObjectOfType on Unity 2022.3+

• Symptom: a deprecation warning at compile time (and eventual removal), plus a silent per-call cost.
• Cause: FindObjectOfType / FindObjectsOfType were deprecated in Unity 2022.3 in favour of FindObjectsByType(FindObjectsSortMode), which makes the sort explicit — the old API always sorted by InstanceID, an avoidable cost. On 6000.4+, FindFirstObjectByType is itself being deprecated, so pinning to it is not future-proof.
• Detect: grep -rn "FindObjectOfType\b" <project>/Assets --include=*.cs — the replacement is FindObjectsByType with an explicit FindObjectsSortMode.
• Severity: medium (2022.3+); high on 6000.4+ where FindFirstObjectByType is also deprecated.

12. CanvasScaler left on Constant Pixel Size

• Symptom: UI does not scale across resolutions — correct in the editor Game view, wrong on device.
• Cause: a CanvasScaler on Constant Pixel Size (m_UiScaleMode: 0) sizes UI in fixed pixels and does not adapt to different resolutions/DPI. Scale With Screen Size (m_UiScaleMode: 1) is almost always the intended mode for multi-resolution UI.
• Detect: grep -rn "m_UiScaleMode: 0" <project>/Assets --include=*.unity --include=*.prefab (0 = ConstantPixelSize; 1 = ScaleWithScreenSize).
• Severity: medium.

13. Empty OnGUI() methods

• Symptom: measurable per-frame overhead with no visible benefit.
• Cause: any OnGUI — even an empty body — routes the component through the IMGUI event loop, which invokes it several times per frame (Layout + Repaint + input events) and allocates. A leftover or empty OnGUI is pure waste on every frame.
• Detect: grep -rn "void OnGUI" <project>/Assets --include=*.cs, then check for empty or near-empty bodies.
• Severity: medium (per-frame cost).

14. IL2CPP reflection target missing [Preserve]

• Symptom: a method reached only via reflection returns null / is not found in IL2CPP player builds, though it works in the editor. No compile error, no exception until the reflection call fails — and only in the build.
• Cause: IL2CPP's managed-code stripping removes members with no static call site. A method invoked purely through reflection (GetMethod + Invoke) is stripped unless annotated with [Preserve] or covered by a link.xml.
• Detect: grep -rn "GetMethod\|MethodInfo\|\.Invoke(" <project>/Assets --include=*.cs, then confirm the reflected target types/members carry [Preserve]. (See also review-safety, which flags this as a runtime-safety trap.)
• Severity: high (silent, build-only failure).

15. Coroutines where Awaitable is available (Unity 2023.1+)

• Symptom: none functionally — a missed-modernization signal. Coroutines cannot return values, are awkward to cancel, and swallow exceptions.
• Cause: Unity 2023.1+ ships Awaitable, which integrates with async/await, CancellationToken, and structured exception handling. New async-shaped work written as IEnumerator + StartCoroutine forgoes cancellation and error propagation.
• Detect: grep -rn "StartCoroutine\|IEnumerator" <project>/Assets --include=*.cs — only relevant when triage recorded Unity ≥ 2023.1.
• Severity: low (info / modernization).

16. Prefab editing without the LoadPrefabContents / UnloadPrefabContents lifecycle

• Symptom: prefab corruption, or edits from an editor script that don't save or save only partially.
• Cause: editing a prefab asset from an editor script must go PrefabUtility.LoadPrefabContents(path) → mutate the returned root → SaveAsPrefabAsset → UnloadPrefabContents. Mutating a loaded prefab any other way, or skipping the unload, leaks the loaded scene and risks writing a corrupt asset.
• Detect: grep -rn "LoadPrefabContents" <project>/Assets --include=*.cs and confirm every call has a matching UnloadPrefabContents.
• Severity: medium.

17. Unity YAML written with true/false instead of 0/1

• Symptom: a serialized bool/enum field is silently ignored or misread after a hand edit.
• Cause: Unity's YAML serializer writes booleans and enum flags as integers (1/0), not true/false. Hand-editing an asset to : true yields a value Unity does not parse as expected, so the field falls back to its default with no error.
• Detect: grep -rn ": true\|: false" <project>/Assets --include=*.asset --include=*.mat
• Severity: medium. If an asset genuinely needs a value change, route it through the unity-yaml-editing-guide skill — never a freehand edit.

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Output

Write to <project>/.unity-review/report/unity-specific-checklist.md. XR items on a non-XR project are marked n/a.

# Unity Review — Unity-Specific Checklist

| # | Trap | Result | Severity | Affected files |
|---|------|--------|----------|----------------|
| 1 | Prefab Variant fileID override | ✓ / ✗ / n/a | high | ... |
| 2 | ARFoundation AddComponent order | ✓ / ✗ / n/a | high | ... |
| ... | | | | |

## Notes
- (context for each ✗ — one line, no fix)

Keep it under 180 lines.

Boundaries

• Do NOT fix any trap. This skill detects and reports only; remediation is a separate task.
• Do NOT hand-edit .meta or YAML assets to "verify" a trap — detection is read-only. Any asset edit goes through unity-yaml-editing-guide.
• Do NOT evaluate CodeHealth, complexity, or coupling — that is review-metrics.
• Do NOT evaluate asmdef dependency direction / layering — that is review-architecture.
• Do NOT modify project files except under <project>/.unity-review/.

Related

• review-triage — entry point; records the XR stack that gates items 2, 3, 9
• review-architecture — asmdef dependency graph (this skill only checks versionDefines, not layering)
• unity-yaml-editing-guide — the only sanctioned path for editing .meta / YAML assets
• xr-specialist (perspective) — reads this skill's output for review-weekly XR commentary