Add test to reproduce the no default no-arg ctor regression in #491

src/test/java/com/fasterxml/jackson/dataformat/xml/failing/Issue491NoArgCtorDeserRegressionTest.java

@@ -0,0 +1,137 @@
+package com.fasterxml.jackson.dataformat.xml.failing;
+
+import com.fasterxml.jackson.annotation.*;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.module.SimpleModule;
+import com.fasterxml.jackson.dataformat.xml.XmlMapper;
+import com.fasterxml.jackson.dataformat.xml.XmlTestBase;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+
+/**
+ * Reproduces <i>no default no-arg ctor found</i> deserialization regression introduced to {@link XmlMapper} in 2.12.0.
+ *
+ * @see <a href="https://github.com/FasterXML/jackson-dataformat-xml/issues/491">jackson-dataformat-xml issue 491</a>
+ */
+public class Issue491NoArgCtorDeserRegressionTest extends XmlTestBase {
+
+    interface Problem {
+
+        String DEFAULT_TYPE = "about:blank";
+
+        int DEFAULT_STATUS = 500;
+
+        String getType();
+
+        int getStatus();
+
+    }
+
+    static class DefaultProblem implements Problem {
+
+        private final String type;
+
+        private final int status;
+
+        /**
+         * This is required to workaround Jackson's missing support for static
+         * {@link JsonCreator}s in mix-ins. That is, we need to define the
+         * creator on a constructor in the mix-in that is matching with a
+         * constructor here too.
+         *
+         * @see <a href="https://github.com/FasterXML/jackson-databind/issues/1820">jackson-databind issue 1820</a>
+         */
+        DefaultProblem(String type, Integer status) {
+            this.type = type != null ? type : Problem.DEFAULT_TYPE;
+            this.status = status != null ? status : Problem.DEFAULT_STATUS;
+        }
+
+        @Override
+        public String getType() {
+            return type;
+        }
+
+        @Override
+        public int getStatus() {
+            return status;
+        }
+
+    }
+
+    @JsonTypeInfo(
+            use = JsonTypeInfo.Id.NAME,
+            include = JsonTypeInfo.As.EXISTING_PROPERTY,
+            property = "type",
+            defaultImpl = DefaultProblem.class,
+            visible = true)
+    @JsonInclude(JsonInclude.Include.NON_EMPTY)
+    @JsonRootName("problem")
+    interface ProblemMixIn extends Problem {
+
+        @Override
+        @JsonProperty("type")
+        String getType();
+
+        @Override
+        @JsonProperty("status")
+        int getStatus();
+
+    }
+
+    abstract static class DefaultProblemMixIn extends DefaultProblem {
+
+        @JsonCreator
+        DefaultProblemMixIn(
+                @JsonProperty("type") String type,
+                @JsonProperty("status") Integer status) {
+            super(type, status);
+            throw new IllegalStateException(
+                    "mix-in constructor is there only for extracting the JSON mapping, " +
+                            "it should not have been called");
+        }
+
+    }
+
+    static class ProblemModule extends SimpleModule {
+
+        @Override
+        public void setupModule(SetupContext context) {
+            super.setupModule(context);
+            registerMixIns(context);
+        }
+
+        private static void registerMixIns(SetupContext context) {
+            context.setMixInAnnotations(DefaultProblem.class, DefaultProblemMixIn.class);
+            context.setMixInAnnotations(Problem.class, ProblemMixIn.class);
+        }
+
+    }
+
+    private static final ProblemModule MODULE = new ProblemModule();
+
+    private static final ObjectMapper JSON_MAPPER = new ObjectMapper().registerModule(MODULE);
+
+    private static final XmlMapper XML_MAPPER = (XmlMapper) new XmlMapper().registerModule(MODULE);
+
+    /**
+     * Passes on 2.11.4 and 2.12.{0..4}.
+     */
+    public void test_empty_Problem_JSON_deserialization() throws IOException {
+        byte[] problemJsonBytes = "{}".getBytes(StandardCharsets.UTF_8);
+        Problem problem = JSON_MAPPER.readValue(problemJsonBytes, Problem.class);
+        assertEquals(Problem.DEFAULT_TYPE, problem.getType());
+        assertEquals(Problem.DEFAULT_STATUS, problem.getStatus());
+    }
+
+    /**
+     * Passes on 2.11.4, but fails on 2.12.{0..4}.
+     */
+    public void test_empty_Problem_XML_deserialization() throws IOException {
+        byte[] problemXmlBytes = "<problem/>".getBytes(StandardCharsets.UTF_8);
+        Problem problem = XML_MAPPER.readValue(problemXmlBytes, Problem.class);
+        assertEquals(Problem.DEFAULT_TYPE, problem.getType());
+        assertEquals(Problem.DEFAULT_STATUS, problem.getStatus());
+    }
+
+}