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style-spec-parity

Coding & development

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Updated 10-16 00:05

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Style spec parity

MapLibre GL JS and MapLibre Native implement the style spec at different paces. Properties on shared layer types stay in the common API, with unsupported writes filtered by StyleBinding. A whole layer type that only one engine accepts has its composable in that engine's source set.

mise run style-spec:parity reads v8.json at the pinned maplibre-style-spec release and compares it with every Main source set that writes a layer or source.

mise run style-spec:parity
mise run style-spec:parity -- --check
mise run style-spec:parity -- --spec /path/to/v8.json

--check fails when a layer type, source type, or paint or layout property that the pinned engines implement is missing on an engine that implements it, written with the other kind, or wrapped in a setter that nothing calls, or when the native unsupported table disagrees with pinned support.

A sdk-support version counts only when it is at most the pin. maplibre-js in gradle/libs.versions.toml is the GL JS pin, and maplibre-styleSpec pins the spec release the catalog reads: the one the pinned maplibre-gl release depends on, so bump both together. The FFI pin is a date stamp, so a recorded Android or iOS release counts as native support, and the pinned spec release keeps that from running ahead of the shipped engines. Properties that exist only in a newer GL JS than the pin stay out of scope until that pin moves.

GL JS parses every property in the pinned spec, because that release is the one it bundles. A property only native renders is therefore still written in commonMain; the catalog lists it as stored but not rendered on js.

Types the spec does not list, spec types this API does not construct, and spec properties this API writes under another name belong in the extra, omitted, and alias sets in ci/style_spec_parity.py. Read those sets and the catalog for the current list.

Read the catalog

Each spec property's sdk-support.basic functionality field is a version string on engines that implement it, and an issue URL on engines that do not.

  • js and native both implement it at the pins. Write the property in commonMain with the matching setPaintProperty or setLayoutProperty.
  • js implements it, native does not. Write it in commonMain and list it on the native binding so a write cannot refuse the whole layer.
  • Native renders a property that JS only stores. Keep the property in commonMain and document the rendering difference. A whole layer type that JS cannot accept follows the separate layer-type guidance below.

Style-root objects

The light, sky, and projection objects at the style root are typed classes in lib/maplibre-compose/src/commonMain/kotlin/org/maplibre/compose/style/, one file per object, each writing its properties with putExpression. The catalog checks every spec property of those objects against the writes in that file. An engine that lacks a whole object reports it through the supportsSky-style flag on StyleBinding rather than the native table. terrain is in the omitted set until the API exposes it.

Add a property both engines implement

  1. Add the composable parameter and a setter that calls setLayoutProperty or setPaintProperty with the spec name. Follow the surrounding layer. A new enum belongs next to the others in lib/maplibre-compose/src/commonMain/kotlin/org/maplibre/compose/expressions/value/.
  2. Default to the spec default when writing it on native is safe. Use nil() when the property is optional and an unset value should stay absent.
  3. Add a liveMapTest round-trip case in LayerPropertyRoundTripTest. Native and GL JS sometimes report the same value in different JSON shapes; the Case helper takes a GL JS form for that.

Add a property native lacks

Keep the setter in commonMain. The binding decides what reaches the engine.

  1. Default the composable parameter to nil(). A spec default that is always written would log an unsupported warning on every layer of that type.
  2. Note on the parameter that it is not yet supported on native, with the issue link from sdk-support.
  3. Add a row to MlnFfiStyleBinding.UNSUPPORTED_LAYER_PROPERTIES. The reason string is what the layer logs once.
  4. Add the round-trip case to the glJsOnly* list in LayerPropertyRoundTripTest, so desktop does not assert a write native will skip.

UnsupportedLayerPropertyTest covers the drop-versus-refuse mechanism. Do not add a case per table row.

A value one engine rejects, on a property it otherwise implements, stays out of that table. skipUnsupportedProperty or the live StyleMutationException handler covers a rejected value.

When a later native release implements the property, delete the table row and move the test from the glJsOnly* list into the shared cases.

Add a layer type one engine lacks

A whole type has no binding filter like a property does. Put the public composable in the source set that has the engine:

  • Native only: maplibreNativeMain, as LocationIndicatorLayer does. The internal Layer class can stay in commonMain so style reconstruction and native tests share it.
  • GL JS only: jsMain.

The other platform's demo or helper uses expect/actual when it needs a stand-in, the way NativeLocationIndicator falls back to nothing on the browser.

Verify

mise run style-spec:parity -- --check
mise run test:desktop
mise run test:js
mise run check

Run mise run ci:test-scripts when changing the catalog checker. For catalog or documentation-only changes, select the relevant checks without running map suites whose behavior is unchanged. Browser setup and test constraints are in AGENTS.md.