Fix collection type resolution in DefaultConfiguratorRegistry

plugin/src/main/java/io/jenkins/plugins/casc/impl/DefaultConfiguratorRegistry.java

@@ -95,20 +95,15 @@ private Configurator internalLookup(Type type) {
             }
         }
 
-        // TODO: Only try to cast if we can actually get the parameterized type
-        if (Collection.class.isAssignableFrom(clazz) && type instanceof ParameterizedType) {
-            ParameterizedType pt = (ParameterizedType) type;
-            Type actualType = pt.getActualTypeArguments()[0];
-            if (actualType instanceof WildcardType) {
-                actualType = ((WildcardType) actualType).getUpperBounds()[0];
+        if (Collection.class.isAssignableFrom(clazz)) {
+            Type collectionType = Types.getBaseClass(type, Collection.class);
+            if (collectionType instanceof ParameterizedType pt) {
+                Type actualType = pt.getActualTypeArguments()[0];
+                if (actualType instanceof WildcardType wildcardType) {
+                    actualType = wildcardType.getUpperBounds()[0];
+                }
+                return internalLookup(actualType); // cache is not reëntrant
             }
-            if (actualType instanceof ParameterizedType) {
-                actualType = ((ParameterizedType) actualType).getRawType();
-            }
-            if (!(actualType instanceof Class)) {
-                throw new IllegalStateException("Can't handle " + type);
-            }
-            return internalLookup(actualType); // cache is not reëntrant
         }
 
         if (Configurable.class.isAssignableFrom(clazz)) {

plugin/src/test/java/io/jenkins/plugins/casc/impl/DefaultConfiguratorRegistryTest.java

@@ -0,0 +1,112 @@
+package io.jenkins.plugins.casc.impl;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import hudson.tasks.Builder;
+import io.jenkins.plugins.casc.Configurator;
+import io.jenkins.plugins.casc.impl.configurators.HeteroDescribableConfigurator;
+import io.jenkins.plugins.casc.impl.configurators.PrimitiveConfigurator;
+import java.lang.reflect.Type;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.jvnet.hudson.test.JenkinsRule;
+
+public class DefaultConfiguratorRegistryTest {
+
+    @Rule
+    public JenkinsRule j = new JenkinsRule();
+
+    private DefaultConfiguratorRegistry registry;
+
+    @Before
+    public void setUp() {
+        registry = new DefaultConfiguratorRegistry();
+    }
+
+    @SuppressWarnings("unused")
+    public static class DummyTarget<T extends Builder> {
+        @SuppressWarnings("rawtypes")
+        public List rawList;
+
+        public List<List<String>> nestedList;
+        public List<? extends Builder> wildcardList;
+        public List<T> typeVarList;
+        public List<?> unknownList;
+    }
+
+    public static class StringList extends ArrayList<String> {}
+
+    private Type getTypeOf(String fieldName) throws NoSuchFieldException {
+        return DummyTarget.class.getDeclaredField(fieldName).getGenericType();
+    }
+
+    @Test
+    public void shouldSafelyHandleRawCollections() throws Exception {
+        Type rawListType = getTypeOf("rawList");
+
+        Configurator<?> configurator = registry.lookup(rawListType);
+
+        assertNull("Raw collections should safely fall through and return null", configurator);
+    }
+
+    @Test
+    public void shouldSafelyExtractNestedGenerics() throws Exception {
+        Type nestedListType = getTypeOf("nestedList");
+
+        Configurator<?> configurator = registry.lookup(nestedListType);
+
+        assertNotNull("Configurator should be found for nested generic", configurator);
+        assertTrue("Should resolve to PrimitiveConfigurator", configurator instanceof PrimitiveConfigurator);
+        assertEquals("Target should resolve exactly to String.class", String.class, configurator.getTarget());
+    }
+
+    @Test
+    public void shouldSafelyExtractWildcardUpperBounds() throws Exception {
+        Type wildcardListType = getTypeOf("wildcardList");
+
+        Configurator<?> configurator = registry.lookup(wildcardListType);
+
+        assertNotNull("Configurator should be found for wildcard", configurator);
+        assertTrue(
+                "Should resolve to HeteroDescribableConfigurator",
+                configurator instanceof HeteroDescribableConfigurator);
+        assertEquals("Target should resolve exactly to Builder.class", Builder.class, configurator.getTarget());
+    }
+
+    @Test
+    public void shouldSafelyExtractTypeVariables() throws Exception {
+        Type typeVarListType = getTypeOf("typeVarList");
+
+        Configurator<?> configurator = registry.lookup(typeVarListType);
+
+        assertNotNull("Configurator should be found for TypeVariable", configurator);
+        assertTrue(
+                "Should resolve to HeteroDescribableConfigurator",
+                configurator instanceof HeteroDescribableConfigurator);
+        assertEquals("Target should resolve exactly to Builder.class", Builder.class, configurator.getTarget());
+    }
+
+    @Test
+    public void shouldHandleCustomCollectionSubclass() {
+        Configurator<?> configurator = registry.lookup(StringList.class);
+
+        assertNotNull("Configurator should be found for custom collection subclass", configurator);
+        assertTrue("Should resolve to PrimitiveConfigurator", configurator instanceof PrimitiveConfigurator);
+        assertEquals("Target should resolve exactly to String.class", String.class, configurator.getTarget());
+    }
+
+    @Test
+    public void shouldSafelyHandleUnboundedWildcards() throws Exception {
+        Type unknownListType = getTypeOf("unknownList");
+
+        Configurator<?> configurator = registry.lookup(unknownListType);
+
+        assertNull("Unbounded wildcards resolve to Object and should safely return null", configurator);
+    }
+}