fix empty builder generation (#129)

Prior to this change if a record or java bean had no properties a duplicate constructor was generated, one for the default constructor and another for an empty list properties. This resulted in a compilation error for duplicate constructors. This fixes that.

sourcegen-generator/src/main/java/io/micronaut/sourcegen/generator/visitors/BuilderAnnotationVisitor.java

@@ -108,7 +108,9 @@ public void visitClass(ClassElement element, VisitorContext context) {
             }
 
             builder.addMethod(MethodDef.constructor().build());
-            builder.addMethod(createAllPropertiesConstructor(builderType, properties));
+            if (!properties.isEmpty()) {
+                builder.addMethod(createAllPropertiesConstructor(builderType, properties));
+            }
 
             builder.addMethod(createBuilderMethod(builderType));
             builder.addMethod(createBuildMethod(element));

sourcegen-generator/src/main/java/io/micronaut/sourcegen/generator/visitors/SuperBuilderAnnotationVisitor.java

@@ -151,6 +151,7 @@ public void visitClass(ClassElement element, VisitorContext context) {
 
                 builder.addMethod(createSelfMethod());
                 builder.addMethod(BuilderAnnotationVisitor.createBuildMethod(element));
+                builder.addMethod(createBuilderMethod(builderType));
 
                 ClassDef builderDef = builder.build();
                 context.visitGeneratedSourceFile(builderDef.getPackageName(), builderDef.getSimpleName(), element).ifPresent(sourceFile -> {
@@ -178,6 +179,14 @@ public void visitClass(ClassElement element, VisitorContext context) {
         }
     }
 
+    private MethodDef createBuilderMethod(ClassTypeDef builderType) {
+        return MethodDef.builder("builder")
+            .addModifiers(Modifier.PUBLIC, Modifier.STATIC)
+            .returns(builderType)
+            .addStatement(builderType.instantiate().returning())
+            .build();
+    }
+
     private MethodDef createSelfMethod() {
         return MethodDef.builder("self")
             .addModifiers(Modifier.PUBLIC)

sourcegen-generator/src/test/groovy/io/micronaut/sourcegen/generator/visitors/BuilderAnnotationVisitorSpec.groovy

@@ -29,4 +29,22 @@ class BuilderAnnotationVisitorSpec extends AbstractTypeElementSpec {
         walrus.age == 1
     }
 
+    void "test empty builder"() {
+        given:
+        var classLoader = buildClassLoader("test.Walrus", """
+        package test;
+        import io.micronaut.sourcegen.annotations.Builder;
+
+        @Builder
+        public record Walrus() {
+        }
+        """)
+        var walrusBuilderClass = classLoader.loadClass("test.WalrusBuilder")
+
+        expect:
+        var walrusBuilder = walrusBuilderClass.newInstance(new Object[]{})
+        var walrus = walrusBuilder.build()
+        walrus != null
+    }
+
 }

test-suite-java/src/main/java/io/micronaut/sourcegen/example/EmptyChild.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2017-2024 original 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 io.micronaut.sourcegen.example;
+
+
+import io.micronaut.sourcegen.annotations.SuperBuilder;
+
+@SuperBuilder
+public class EmptyChild extends EmptyParent {
+}

test-suite-java/src/main/java/io/micronaut/sourcegen/example/EmptyParent.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2017-2024 original 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 io.micronaut.sourcegen.example;
+
+import io.micronaut.sourcegen.annotations.SuperBuilder;
+
+@SuperBuilder
+public class EmptyParent {
+}

test-suite-java/src/main/java/io/micronaut/sourcegen/example/EmptyThing.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2017-2024 original 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 io.micronaut.sourcegen.example;
+
+import io.micronaut.sourcegen.annotations.Builder;
+
+@Builder
+public class EmptyThing {
+}

test-suite-java/src/test/java/io/micronaut/sourcegen/example/EmptyTest.java

@@ -0,0 +1,19 @@
+package io.micronaut.sourcegen.example;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class EmptyTest {
+
+    @Test
+    void testEmptyBuilder() {
+        EmptyThing built = EmptyThingBuilder.builder().build();
+        Assertions.assertNotNull(built);
+    }
+
+    @Test
+    void testEmptySuperBuilder() {
+        EmptyChild built = EmptyChildSuperBuilder.builder().build();
+        Assertions.assertNotNull(built);
+    }
+}