Allow empty list injection

config/config/src/main/java/io/helidon/config/ConfigProducer.java

@@ -26,9 +26,6 @@
 import io.helidon.common.config.GlobalConfig;
 import io.helidon.config.spi.ConfigSource;
 import io.helidon.pico.api.ExternalContracts;
-import io.helidon.pico.api.PicoServices;
-import io.helidon.pico.api.ServiceInfoCriteria;
-import io.helidon.pico.api.ServiceProvider;
 
 import jakarta.inject.Inject;
 import jakarta.inject.Provider;
@@ -40,13 +37,7 @@ class ConfigProducer implements Config {
     private final Config config;
 
     @Inject
-    ConfigProducer() {
-        // this should be moved to constructor injection when we support zero length lists for injection
-        List<ServiceProvider<?>> serviceProviders = PicoServices.realizedServices()
-                .lookupAll(ServiceInfoCriteria
-                                   .builder()
-                                   .addContractImplemented(ConfigSource.class).build(), false);
-
+    ConfigProducer(List<Provider<ConfigSource>> serviceProviders) {
         if (GlobalConfig.configured()) {
             config = GlobalConfig.config();
         } else {

pico/api/src/main/java/io/helidon/pico/api/ServiceInjectionPlanBinder.java

@@ -53,7 +53,7 @@ Binder bind(String id,
         * It is assumed that the caller of this is aware of the proper cardinality for each injection point.
         *
         * @param id                 the injection point identity
-        * @param serviceProviders   the list of service providers to bind to this identity.
+        * @param serviceProviders   the list of service providers to bind to this identity
         * @return the binder builder
         */
         Binder bindMany(String id,

pico/runtime/src/main/java/io/helidon/pico/runtime/DefaultInjectionPlans.java

@@ -407,6 +407,11 @@ private static boolean isSelf(ServiceProvider<?> self,
     }
 
     private static boolean allowNullableInjectionPoint(InjectionPointInfo ipInfo) {
+        if (ipInfo.listWrapped()) {
+            // allow empty lists to be injected
+            return true;
+        }
+
         ServiceInfoCriteria missingServiceInfo = ipInfo.dependencyToServiceInfo();
         Set<TypeName> contractsNeeded = missingServiceInfo.contractsImplemented();
         return (1 == contractsNeeded.size() && contractsNeeded.contains(INTERCEPTOR));

pico/tests/resources-pico/src/main/java/io/helidon/pico/tests/pico/AContractWithNoServiceImplementations.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2023 Oracle and/or its affiliates.
+ *
+ * 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
+ *
+ *     http://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 io.helidon.pico.tests.pico;
+
+import io.helidon.pico.api.Contract;
+
+@Contract
+interface AContractWithNoServiceImplementations {
+}

pico/tests/resources-pico/src/main/java/io/helidon/pico/tests/pico/AServiceUsingAContractWithNoServiceImplementations.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2023 Oracle and/or its affiliates.
+ *
+ * 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
+ *
+ *     http://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 io.helidon.pico.tests.pico;
+
+import java.util.List;
+
+import jakarta.inject.Inject;
+import jakarta.inject.Provider;
+import jakarta.inject.Singleton;
+
+@Singleton
+class AServiceUsingAContractWithNoServiceImplementations {
+
+    @Inject
+    AServiceUsingAContractWithNoServiceImplementations(List<Provider<AContractWithNoServiceImplementations>> list) {
+        if (!list.isEmpty()) {
+            throw new AssertionError("Should be empty: " + list);
+        }
+    }
+
+}

pico/tests/resources-pico/src/test/java/io/helidon/pico/tests/pico/EmptyListInjectionTest.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2023 Oracle and/or its affiliates.
+ *
+ * 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
+ *
+ *     http://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 io.helidon.pico.tests.pico;
+
+import io.helidon.config.Config;
+import io.helidon.pico.api.ServiceProvider;
+import io.helidon.pico.api.Services;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static io.helidon.pico.testing.PicoTestingSupport.basicTestableConfig;
+import static io.helidon.pico.testing.PicoTestingSupport.resetAll;
+import static io.helidon.pico.testing.PicoTestingSupport.testableServices;
+import static org.hamcrest.CoreMatchers.notNullValue;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+class EmptyListInjectionTest {
+    private static final Config CONFIG = basicTestableConfig();
+
+    private Services services;
+
+    @BeforeEach
+    void setUp() {
+        this.services = testableServices(CONFIG).services();
+    }
+
+    @AfterEach
+    void tearDown() {
+        resetAll();
+    }
+
+    @Test
+    void acceptEmptyListInjectables() {
+        ServiceProvider<AServiceUsingAContractWithNoServiceImplementations> sp =
+                services.lookupFirst(AServiceUsingAContractWithNoServiceImplementations.class);
+        assertThat(sp.get(), notNullValue());
+    }
+
+}

pico/tools/src/main/java/io/helidon/pico/tools/ApplicationCreatorDefault.java

@@ -348,15 +348,15 @@ List<String> toInjectionPlanBindings(ServiceProvider<?> sp) {
             List<?> ipUnqualified = e.getValue().unqualifiedProviders();
             boolean resolved = false;
             try {
-                if (ipQualified.isEmpty()) {
+                if (ipInfo.listWrapped()) {
+                    line.append(".bindMany(");
+                } else if (ipQualified.isEmpty()) {
                     if (!ipUnqualified.isEmpty()) {
                         resolved = true;
                         line.append(".resolvedBind(");
                     } else {
                         line.append(".bindVoid(");
                     }
-                } else if (ipInfo.listWrapped()) {
-                    line.append(".bindMany(");
                 } else {
                     line.append(".bind(");
                 }