Fix #185 GuavaCollectionDeserializer does not respect JsonFormat.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY (#193)

Author: JooHyukKim

guava/src/main/java/com/fasterxml/jackson/datatype/guava/deser/GuavaCollectionDeserializer.java

@@ -138,9 +138,12 @@ public T deserialize(JsonParser p, DeserializationContext ctxt)
             return _deserializeContents(p, ctxt);
         }
         // But may support implicit arrays from single values?
-        if (ctxt.isEnabled(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY)) {
+        final boolean canWrap = (_unwrapSingle == Boolean.TRUE) ||
+                ((_unwrapSingle == null) && ctxt.isEnabled(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY));
+        if (canWrap) {
             return _deserializeFromSingleValue(p, ctxt);
         }
+        // Otherwise, we have a problem
         return (T) ctxt.handleUnexpectedToken(_valueClass, p);
     }
 

guava/src/test/java/com/fasterxml/jackson/datatype/guava/ImmutableListAcceptSingle185Test.java

@@ -0,0 +1,57 @@
+package com.fasterxml.jackson.datatype.guava;
+
+import java.util.List;
+
+import com.google.common.collect.ImmutableList;
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.annotation.JsonFormat;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+// [datatype-guava#185] : `GuavaCollectionDeserializer` does not respect
+// `JsonFormat.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY`
+public class ImmutableListAcceptSingle185Test
+    extends ModuleTestBase
+{
+    static class Line {
+        public String data;
+    }
+
+    static class GuavaContainer185 {
+        @JsonFormat(with = JsonFormat.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY)
+        public ImmutableList<Line> lines;
+    }
+
+    static class JavaContainer185 {
+        @JsonFormat(with = JsonFormat.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY)
+        public List<Line> lines;
+    }
+
+    private final ObjectMapper MAPPER = mapperWithModule();
+
+    // Sanity Check, JDK List works by default
+    @Test
+    public void testJDKListWithSingleValue()
+            throws Exception
+    {
+        String json = "{\"lines\":{\"data\":\"something-jdk\"}}";
+
+        JavaContainer185 javaContainer = MAPPER.readValue(json, JavaContainer185.class);
+        assertEquals(1, javaContainer.lines.size());
+        assertEquals("something-jdk", javaContainer.lines.get(0).data);
+    }
+
+    // Guava's ImmutableList does not work, but should
+    @Test
+    public void testGuavaImmutableListWithSingleValue()
+            throws Exception
+    {
+        String json = "{\"lines\":{\"data\":\"something-guava\"}}";
+
+        GuavaContainer185 container = MAPPER.readValue(json, GuavaContainer185.class);
+        assertEquals(1, container.lines.size());
+        assertEquals("something-guava", container.lines.get(0).data);
+    }
+}