Bug fix: collection/map spec with subtype throws exception from GeneratorProvider SPI

instancio-core/src/main/java/org/instancio/internal/generator/util/CollectionGeneratorSpecImpl.java

@@ -18,6 +18,7 @@
 import org.instancio.Random;
 import org.instancio.exception.InstancioException;
 import org.instancio.generator.GeneratorContext;
+import org.instancio.internal.util.ReflectionUtils;
 
 import java.util.Collection;
 
@@ -32,7 +33,11 @@ public CollectionGeneratorSpecImpl(final GeneratorContext context) {
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     protected Collection<T> tryGenerateNonNull(final Random random) {
+        if (collectionType != null) {
+            return (Collection<T>) ReflectionUtils.newInstance(collectionType);
+        }
         throw new InstancioException(getClass() + " should delegate to another generator");
     }
 }

instancio-core/src/main/java/org/instancio/internal/generator/util/MapGeneratorSpecImpl.java

@@ -18,6 +18,7 @@
 import org.instancio.Random;
 import org.instancio.exception.InstancioException;
 import org.instancio.generator.GeneratorContext;
+import org.instancio.internal.util.ReflectionUtils;
 
 import java.util.Map;
 
@@ -32,7 +33,11 @@ public MapGeneratorSpecImpl(final GeneratorContext context) {
     }
 
     @Override
+    @SuppressWarnings("unchecked")
     public Map<K, V> tryGenerateNonNull(final Random random) {
+        if (mapType != null) {
+            return (Map<K, V>) ReflectionUtils.newInstance(mapType);
+        }
         throw new InstancioException(getClass() + " should delegate to another generator");
     }
 }

instancio-core/src/main/java/org/instancio/internal/util/ReflectionUtils.java

@@ -21,6 +21,7 @@
 import org.slf4j.LoggerFactory;
 
 import java.lang.reflect.AccessibleObject;
+import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
@@ -177,5 +178,14 @@ public static Class<?> getClass(final String name) {
             throw Fail.withUsageError("failed loading class: '%s'", name, ex);
         }
     }
+
+    public static <T> T newInstance(final Class<T> klass) {
+        try {
+            final Constructor<T> ctor = klass.getDeclaredConstructor();
+            return ctor.newInstance();
+        } catch (Exception ex) {
+            throw new InstancioException("Error instantiating " + klass, ex);
+        }
+    }
 }
 

instancio-tests/instancio-core-tests/src/test/java/org/instancio/internal/generator/util/CollectionGeneratorSpecImplTest.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2022-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.instancio.internal.generator.util;
+
+import org.instancio.Random;
+import org.instancio.exception.InstancioException;
+import org.instancio.generator.GeneratorContext;
+import org.instancio.settings.Settings;
+import org.instancio.support.DefaultRandom;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class CollectionGeneratorSpecImplTest {
+
+    private final Random random = new DefaultRandom();
+    private final GeneratorContext context = new GeneratorContext(Settings.defaults(), random);
+
+    private final CollectionGeneratorSpecImpl<?> generator = new CollectionGeneratorSpecImpl<>(context);
+
+    @Test
+    void shouldFailIfNoSubtypeIsProvided() {
+        assertThatThrownBy(() -> generator.generate(random))
+                .isExactlyInstanceOf(InstancioException.class)
+                .hasMessage("%s should delegate to another generator", generator.getClass());
+    }
+
+    @Test
+    void shouldCreateANewInstanceIfSubtypeIsProvided() {
+        generator.subtype(ArrayList.class);
+
+        assertThat(generator.generate(random)).isInstanceOf(ArrayList.class);
+    }
+}

instancio-tests/instancio-core-tests/src/test/java/org/instancio/internal/generator/util/MapGeneratorSpecImplTest.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2022-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.instancio.internal.generator.util;
+
+import org.instancio.Random;
+import org.instancio.exception.InstancioException;
+import org.instancio.generator.GeneratorContext;
+import org.instancio.settings.Settings;
+import org.instancio.support.DefaultRandom;
+import org.junit.jupiter.api.Test;
+
+import java.util.TreeMap;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class MapGeneratorSpecImplTest {
+
+    private final Random random = new DefaultRandom();
+    private final GeneratorContext context = new GeneratorContext(Settings.defaults(), random);
+
+    private final MapGeneratorSpecImpl<?, ?> generator = new MapGeneratorSpecImpl<>(context);
+
+    @Test
+    void shouldFailIfNoSubtypeIsProvided() {
+        assertThatThrownBy(() -> generator.generate(random))
+                .isExactlyInstanceOf(InstancioException.class)
+                .hasMessage("%s should delegate to another generator", generator.getClass());
+    }
+
+    @Test
+    void shouldCreateANewInstanceIfSubtypeIsProvided() {
+        generator.subtype(TreeMap.class);
+
+        assertThat(generator.generate(random)).isInstanceOf(TreeMap.class);
+    }
+}

instancio-tests/spi-tests/src/test/java/org/example/spi/CustomGeneratorProvider.java

@@ -32,6 +32,8 @@
 import org.instancio.spi.InstancioServiceProvider;
 import org.instancio.spi.ServiceProviderContext;
 import org.instancio.test.support.pojo.arrays.object.WithIntegerArray;
+import org.instancio.test.support.pojo.collections.lists.ListInteger;
+import org.instancio.test.support.pojo.collections.maps.MapIntegerItemOfString;
 import org.instancio.test.support.pojo.collections.maps.MapIntegerString;
 import org.instancio.test.support.pojo.collections.sets.SetInteger;
 import org.instancio.test.support.pojo.dynamic.DynPhone;
@@ -43,8 +45,11 @@
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.TreeMap;
 import java.util.regex.Pattern;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -116,6 +121,14 @@ private static class GeneratorProviderImpl implements GeneratorProvider {
         public GeneratorSpec<?> getGenerator(final Node node, final Generators generators) {
             if (node.getField() != null) {
 
+                // Ensure collection/map generators work with subtype()
+                if (node.getParent().getTargetClass() == ListInteger.class && node.getField().getType() == List.class) {
+                    return generators.collection().subtype(LinkedList.class);
+                }
+                if (node.getParent().getTargetClass() == MapIntegerItemOfString.class && node.getField().getType() == Map.class) {
+                    return generators.map().subtype(TreeMap.class);
+                }
+
                 if (node.getParent().getTargetClass() == SetInteger.class && node.getField().getType() == Set.class) {
                     return generators.collection().size(10);
                 }

instancio-tests/spi-tests/src/test/java/org/instancio/spi/tests/GeneratorFromSpiTest.java

@@ -33,6 +33,8 @@
 import org.instancio.spi.InstancioSpiException;
 import org.instancio.test.support.pojo.arrays.object.WithIntegerArray;
 import org.instancio.test.support.pojo.basic.IntegerHolder;
+import org.instancio.test.support.pojo.collections.lists.ListInteger;
+import org.instancio.test.support.pojo.collections.maps.MapIntegerItemOfString;
 import org.instancio.test.support.pojo.collections.maps.MapIntegerString;
 import org.instancio.test.support.pojo.collections.sets.SetInteger;
 import org.instancio.test.support.pojo.dynamic.DynPhone;
@@ -52,8 +54,10 @@
 import java.lang.reflect.Field;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.TreeMap;
 import java.util.regex.Pattern;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -334,6 +338,23 @@ void mapSpecWithImmutableMap() {
                 .hasSize(10);
     }
 
+    @Nested
+    class SpecsWithSubtypeTest {
+        @Test
+        void collectionSpecWithSubtype() {
+            final ListInteger result = Instancio.create(ListInteger.class);
+
+            assertThat(result.getList()).isExactlyInstanceOf(LinkedList.class);
+        }
+
+        @Test
+        void mapSpecWithSubtype() {
+            final MapIntegerItemOfString result = Instancio.create(MapIntegerItemOfString.class);
+
+            assertThat(result.getMap()).isExactlyInstanceOf(TreeMap.class);
+        }
+    }
+
     /**
      * Generator provider returning {@link Generators#array()}.
      */