Minor tweaks to #3418

Author: cowtowncoder

src/test/java/com/fasterxml/jackson/databind/convert/CoerceContainersTest.java

@@ -29,7 +29,22 @@ public void testScalarCollections() throws Exception
     {
         final JavaType listType = VANILLA_MAPPER.getTypeFactory()
                 .constructType(new TypeReference<List<Double>>() { });
-        _verifyNoCoercion(listType);
+        
+        // 03-Aug-2022, tatu: Due to [databind#3418] message changed; not
+        //    100% sure how it should work but let's try this
+        
+//        _verifyNoCoercion(listType);
+        try {
+            VANILLA_MAPPER.readerFor(listType).readValue(JSON_EMPTY);
+            fail("Should not pass");
+        } catch (DatabindException e) {
+//            verifyException(e, "Cannot coerce empty String");
+            verifyException(e, "Cannot deserialize value of type");
+            verifyException(e, "from String value");
+            e.printStackTrace();
+        }
+
+        
         List<Double> result = _readWithCoercion(listType);
         assertNotNull(result);
         assertEquals(0, result.size());
@@ -159,7 +174,7 @@ private void _verifyNoCoercion(JavaType targetType) throws Exception {
         try {
             VANILLA_MAPPER.readerFor(targetType).readValue(JSON_EMPTY);
             fail("Should not pass");
-        } catch (Exception e) {
+        } catch (DatabindException e) {
             // 06-Nov-2020, tatu: tests for failure get rather fragile unfortunately,
             //   but this seems to be what we should be getting
 

src/test/java/com/fasterxml/jackson/databind/convert/EmptyStringAsSingleValueTest.java

@@ -0,0 +1,116 @@
+package com.fasterxml.jackson.databind.convert;
+
+import java.util.Collections;
+import java.util.List;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+
+import com.fasterxml.jackson.databind.BaseMapTest;
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.cfg.CoercionAction;
+import com.fasterxml.jackson.databind.cfg.CoercionInputShape;
+
+// [databind#3418]: Coercion from empty String to Collection<String>, with
+// `DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY` 
+public class EmptyStringAsSingleValueTest extends BaseMapTest
+{
+    static final class StringWrapper {
+        private final String s;
+
+        @JsonCreator(mode = JsonCreator.Mode.DELEGATING)
+        public StringWrapper(String s) {
+            this.s = s;
+        }
+
+        @Override
+        public String toString() {
+            return "StringWrapper{" + s + "}";
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            return obj instanceof StringWrapper && ((StringWrapper) obj).s.equals(s);
+        }
+
+        @Override
+        public int hashCode() {
+            return s.hashCode();
+        }
+    }
+
+    private final ObjectMapper NORMAL_MAPPER = jsonMapperBuilder()
+            .enable(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY)
+            .build();
+
+    private final ObjectMapper COERCION_MAPPER = jsonMapperBuilder()
+            .enable(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY)
+        // same as XmlMapper
+            .withCoercionConfigDefaults(h -> {
+                h.setAcceptBlankAsEmpty(true)
+                    .setCoercion(CoercionInputShape.EmptyString, CoercionAction.AsEmpty);
+            })
+            .build();
+
+    public void testEmptyToList() throws Exception {
+        // NO coercion + empty string input + StringCollectionDeserializer
+        assertEquals(Collections.singletonList(""),
+                NORMAL_MAPPER.readValue("\"\"", new TypeReference<List<String>>() {}));
+    }
+
+    public void testEmptyToListWrapper() throws Exception {
+        // NO coercion + empty string input + normal CollectionDeserializer
+        assertEquals(Collections.singletonList(new StringWrapper("")),
+                NORMAL_MAPPER.readValue("\"\"", new TypeReference<List<StringWrapper>>() {}));
+    }
+
+    public void testCoercedEmptyToList() throws Exception {
+        // YES coercion + empty string input + StringCollectionDeserializer
+        assertEquals(Collections.emptyList(), COERCION_MAPPER.readValue("\"\"",
+                new TypeReference<List<String>>() {}));
+    }
+
+    public void testCoercedEmptyToListWrapper() throws Exception {
+        // YES coercion + empty string input + normal CollectionDeserializer
+        assertEquals(Collections.emptyList(),
+                COERCION_MAPPER.readValue("\"\"", new TypeReference<List<StringWrapper>>() {}));
+    }
+
+    public void testCoercedListToList() throws Exception {
+        // YES coercion + empty LIST input + StringCollectionDeserializer
+        assertEquals(Collections.emptyList(), 
+                COERCION_MAPPER.readValue("[]", new TypeReference<List<String>>() {}));
+    }
+
+    public void testCoercedListToListWrapper() throws Exception {
+        // YES coercion + empty LIST input + normal CollectionDeserializer
+        assertEquals(Collections.emptyList(),
+                COERCION_MAPPER.readValue("[]", new TypeReference<List<StringWrapper>>() {}));
+    }
+
+    public void testBlankToList() throws Exception {
+        // NO coercion + empty string input + StringCollectionDeserializer
+        assertEquals(Collections.singletonList(" "),
+                NORMAL_MAPPER.readValue("\" \"", new TypeReference<List<String>>() {}));
+    }
+
+    public void testBlankToListWrapper() throws Exception {
+        // NO coercion + empty string input + normal CollectionDeserializer
+        assertEquals(Collections.singletonList(new StringWrapper(" ")),
+                NORMAL_MAPPER.readValue("\" \"", new TypeReference<List<StringWrapper>>() {}));
+    }
+
+    public void testCoercedBlankToList() throws Exception {
+        // YES coercion + empty string input + StringCollectionDeserializer
+        assertEquals(Collections.emptyList(),
+                COERCION_MAPPER.readValue("\" \"", new TypeReference<List<String>>() {}));
+    }
+
+    public void testCoercedBlankToListWrapper() throws Exception {
+        // YES coercion + empty string input + normal CollectionDeserializer
+        assertEquals(Collections.emptyList(),
+                COERCION_MAPPER.readValue("\" \"", new TypeReference<List<StringWrapper>>() {}));
+    }
+}