Keep zoom() at top level in route-stop circle expressions (#1927)

[bmander]

Fixes #1927

Problem

After the MapLibre 11 → 13 upgrade, MapLibreRouteStopCircleLayer fails runtime style-expression validation at launch:

zoom expression may only be used as input to a top-level step or interpolate expression

The layer built a zoom()-driven radius interpolation once, then wrapped that whole interpolation inside product() to derive two properties:

• the outer circle's circleStrokeWidth (radius × stroke/radius ratio)
• the selected-stop inner circle's circleRadius (radius × inner scale)

MapLibre 11.5.2 tolerated a zoom() nested inside product(); 13.3.1 rejects it. The top-level circleRadius() interpolation still validated, so only those two nested usages broke — route-stop circles rendered without their stroke ring, and selected stops lost their zoom-scaled radius highlighting.

Fix

radiusExpression(scale) now folds the scale factor into each interpolation stop output rather than wrapping the interpolation:

interpolate(linear(), zoom(),
    stop(START, get(prop) × scale),
    stop(END,   get(prop) × scale))

zoom() stays at the top level (valid). Because the interpolation is linear, scaling each endpoint is mathematically identical to scaling the whole interpolation — including the clamped regions outside the zoom band. The default scale = 1f reproduces the original bare-get() outputs for the outer radius.

Testing

• ✅ Compiles clean under the CI gate: ./gradlew :onebusaway-android:compileObaMaplibreDebugKotlin -PwarningsAsErrors=true
• This is a MapLibre-runtime style-validation bug with a purely visual symptom, so there is no unit-test surface. Confirming the rendered result (logcat clear of the validation error, stroke rings present, selected-stop highlight scaling with zoom) requires launching the obaMaplibreDebug build on a device.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved map stop-circle rendering across zoom levels.
  • Updated stop markers and outlines to maintain more consistent sizing and proportions as the map scale changes.
  • Improved visual alignment between the outer stop circle, inner circle, and border.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 80859534-491f-440d-82c3-159563fddba9

📥 Commits

Reviewing files that changed from the base of the PR and between 6c71ddd and e75915a.

📒 Files selected for processing (1)

• onebusaway-android/src/maplibre/java/org/onebusaway/android/map/maplibre/MapLibreRouteStopCircleLayer.kt

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📝 Walkthrough

Walkthrough

The route-stop circle layer now applies outer stroke and inner-circle scaling within interpolation stop outputs, preserving a top-level zoom() expression for MapLibre radius and stroke-width properties.

Changes

Stop-circle expression scaling

Layer / File(s)	Summary
Parameterized radius expressions onebusaway-android/src/maplibre/.../MapLibreRouteStopCircleLayer.kt	radiusExpression accepts an optional scale and applies it to interpolation outputs; outer radius, stroke width, and inner radius properties use the parameterized expression.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% 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
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: keeping zoom() top-level in route-stop circle expressions.
Linked Issues check	✅ Passed	The change folds scale into interpolation stops and preserves top-level zoom(), matching issue #1927's required fix.
Out of Scope Changes check	✅ Passed	The PR is limited to the MapLibre route-stop circle expression refactor and stays within the linked issue's scope.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/1927-maplibre-zoom-expression

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