[Fix serverlessworkflow#418] Adding const support

Signed-off-by: Javier <ftirados@redhat.com>

api/pom.xml

@@ -101,6 +101,7 @@
                     <usePrimitives>true</usePrimitives>
                     <useJakartaValidation>true</useJakartaValidation>
                     <customRuleFactory>io.serverlessworkflow.generator.UnreferencedFactory</customRuleFactory>
+                    <customAnnotator>io.serverlessworkflow.generator.ConstAnnotator</customAnnotator>
                 </configuration>
                 <dependencies>
                     <dependency>

api/src/test/java/io/serverlessworkflow/api/ApiTest.java

@@ -18,6 +18,7 @@
 import static io.serverlessworkflow.api.WorkflowReader.readWorkflowFromClasspath;
 import static org.assertj.core.api.Assertions.assertThat;
 
+import io.serverlessworkflow.api.types.CallFunction;
 import io.serverlessworkflow.api.types.CallHTTP;
 import io.serverlessworkflow.api.types.CallTask;
 import io.serverlessworkflow.api.types.Task;
@@ -44,4 +45,22 @@ void testCallHTTPAPI() throws IOException {
       assertThat(httpCall.getWith().getMethod()).isEqualTo("get");
     }
   }
+
+  @Test
+  void testCallFunctionAPIWithoutArguments() throws IOException {
+    Workflow workflow = readWorkflowFromClasspath("features/callFunction.yaml");
+    assertThat(workflow.getDo()).isNotEmpty();
+    assertThat(workflow.getDo().get(0).getName()).isNotNull();
+    assertThat(workflow.getDo().get(0).getTask()).isNotNull();
+    Task task = workflow.getDo().get(0).getTask();
+    CallTask callTask = task.getCallTask();
+    assertThat(callTask).isNotNull();
+    assertThat(callTask.get()).isInstanceOf(CallFunction.class);
+    if (callTask.get() instanceof CallFunction) {
+      CallFunction functionCall = callTask.getCallFunction();
+      assertThat(functionCall).isNotNull();
+      assertThat(callTask.getCallAsyncAPI()).isNull();
+      assertThat(functionCall.getWith()).isNull();
+    }
+  }
 }

api/src/test/java/io/serverlessworkflow/api/FeaturesTest.java

@@ -43,7 +43,8 @@ public class FeaturesTest {
         "features/set.yaml",
         "features/switch.yaml",
         "features/try.yaml",
-        "features/listen.yaml"
+        "features/listen.yaml",
+        "features/callFunction.yaml"
       })
   public void testSpecFeaturesParsing(String workflowLocation) throws IOException {
     Workflow workflow = readWorkflowFromClasspath(workflowLocation);

api/src/test/resources/features/callFunction.yaml

@@ -0,0 +1,18 @@
+document:
+  dsl: 1.0.0-alpha1
+  namespace: default
+  name: http-call-with-response-output
+
+use:
+  functions:
+    getPet:
+      call: http
+      with:
+        method: get
+        endpoint:
+          uri: https://petstore.swagger.io/v2/pet/{petId}
+        output: response
+
+do:
+  - getPetFunctionCall:
+      call: getPet

custom-generator/src/main/java/io/serverlessworkflow/generator/ConstAnnotator.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2020-Present The Serverless Workflow Specification 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
+ *
+ * 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.serverlessworkflow.generator;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.sun.codemodel.JDefinedClass;
+import com.sun.codemodel.JFieldVar;
+import jakarta.validation.constraints.Pattern;
+import org.jsonschema2pojo.AbstractAnnotator;
+import org.jsonschema2pojo.GenerationConfig;
+
+public class ConstAnnotator extends AbstractAnnotator {
+
+  private static final String CONST = "const";
+
+  public ConstAnnotator(GenerationConfig generationConfig) {
+    super(generationConfig);
+  }
+
+  @Override
+  public void propertyField(
+      JFieldVar field, JDefinedClass clazz, String propertyName, JsonNode propertyNode) {
+    if (propertyNode.has(CONST)) {
+      field.annotate(Pattern.class).param("regexp", propertyNode.get(CONST).asText());
+    }
+  }
+}