added dependsOnLayer() ...

planetiler-core/src/main/java/com/onthegomap/planetiler/ForwardingProfile.java

@@ -81,13 +81,38 @@ protected ForwardingProfile(Handler... handlers) {
   }
 
   private boolean caresAboutLayer(String layer) {
-    return (onlyLayers.isEmpty() || onlyLayers.contains(layer)) && !excludeLayers.contains(layer);
+    var dependencies = dependsOnLayer();
+    return ((onlyLayers.isEmpty() || onlyLayers.contains(layer)) && !excludeLayers.contains(layer)) ||
+      this.handlers.stream()
+        .filter(HandlerForLayer.class::isInstance)
+        .map(HandlerForLayer.class::cast)
+        .filter(l -> !l.name().equals(layer))
+        .anyMatch(
+          existing -> dependencies.containsKey(existing.name()) && dependencies.get(existing.name()).contains(layer));
   }
 
   public boolean caresAboutLayer(Object obj) {
     return !(obj instanceof HandlerForLayer l) || caresAboutLayer(l.name());
   }
 
+  /**
+   * Indicate to {@link #caresAboutLayer(String)} what layers (dependents) rely on other layers (dependencies) so that
+   * methods like {@link #registerFeatureHandler(FeatureProcessor)}, {@link #registerHandler(Handler)} or
+   * {@link #registerSourceHandler(String, FeatureProcessor)} do not block registration of those dependencies.
+   * <p>
+   * Dependencies are described as a map with dependent layer names as keys and lists containing dependency layer names
+   * as map values. Example: Layer named {@code transportation_name} depends on layer named {@code transportation}:
+   * <p>
+   * {@snippet :
+   * Map.of("transportation_name", List.of("transportation"));
+   * }
+   *
+   * @return a map describing dependencies
+   */
+  public Map<String, List<String>> dependsOnLayer() {
+    return Map.of();
+  }
+
   /**
    * Call {@code processor} for every element in {@code source}.
    *

planetiler-core/src/test/java/com/onthegomap/planetiler/ForwardingProfileTests.java

@@ -24,6 +24,7 @@
 import java.util.TreeSet;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 import org.junit.jupiter.params.provider.ValueSource;
 
 class ForwardingProfileTests {
@@ -455,4 +456,51 @@ public void processFeature(SourceFeature sourceFeature, FeatureCollector feature
       "_layer", "water"
     )), a);
   }
+
+  @ParameterizedTest
+  @CsvSource({
+    "'--only-layers=water', water",
+    "'--exclude-layers=land,transportation,transportation_name', water",
+    // transportation excluded but transportation_name NOT => transportation will be processed
+    "'--exclude-layers=land,transportation', water transportation_name transportation",
+    "'--exclude-layers=land,transportation_name', water transportation",
+    "'--exclude-layers=land --only-layers=water,land', water",
+    // transportation excluded but transportation_name NOT => transportation will be processed
+    "'--exclude-layers=transportation --only-layers=water,transportation,transportation_name', water transportation_name transportation",
+    "'--exclude-layers=transportation_name --only-layers=water,transportation,transportation_name', water transportation",
+    "'--exclude-layers=transportation,transportation_name --only-layers=water,transportation,transportation_name', water",
+    // transportation excluded but transportation_name NOT => transportation will be processed
+    "'--exclude-layers=transportation --only-layers=water,transportation_name', water transportation_name transportation",
+    "'--exclude-layers=transportation_name --only-layers=water,transportation', water transportation",
+  })
+  void testLayerWithDepsCliArgFilter(String args, String expectedLayers) {
+    profile = new ForwardingProfile(PlanetilerConfig.from(Arguments.fromArgs(args.split(" ")))) {
+      @Override
+      public Map<String, List<String>> dependsOnLayer() {
+        return Map.of("transportation_name", List.of("transportation"));
+      }
+    };
+    record Processor(String name) implements ForwardingProfile.HandlerForLayer, ForwardingProfile.FeatureProcessor {
+
+      @Override
+      public void processFeature(SourceFeature sourceFeature, FeatureCollector features) {
+        features.point(name);
+      }
+    }
+
+    SourceFeature a = SimpleFeature.create(GeoUtils.EMPTY_POINT, Map.of("key", "value"), "source", "source layer", 1);
+    profile.registerHandler(new Processor("water"));
+    profile.registerHandler(new Processor("transportation"));
+    profile.registerHandler(new Processor("transportation_name"));
+    profile.registerHandler(new Processor("land"));
+    // profiles like OpenMapTiles will try to add "transportation" once again to cover for dependency
+    profile.registerHandler(new Processor("transportation"));
+
+    List<Map<String, Object>> expected = new ArrayList<>();
+    for (var expectedLayer : expectedLayers.split(" ")) {
+      expected.add(Map.of("_layer", expectedLayer));
+    }
+
+    testFeatures(expected, a);
+  }
 }