Incorrect target type when disabling coercion, trying to deserialize String from Array/Object

[joca-bt]

When disabling coercions and providing a wrong type on an array element, the error message is specifying that we are trying to coerce the type of the array when it should mention we are trying to coerce the type of the element of the array. See the example below. This is another instance of #3690.

// Test class.
public static class Input<T> {
    private T field;

    public T getField() {
        return field;
    }

    public void setField(T field) {
        this.field = field;
    }
}

// Building a strict ObjectMapper.
ObjectMapper objectMapper = JsonMapper.builder()
    .withCoercionConfigDefaults(config -> {
        config.setCoercion(CoercionInputShape.Boolean, CoercionAction.Fail)
            .setCoercion(CoercionInputShape.Integer, CoercionAction.Fail)
            .setCoercion(CoercionInputShape.Float, CoercionAction.Fail)
            .setCoercion(CoercionInputShape.String, CoercionAction.Fail)
            .setCoercion(CoercionInputShape.Array, CoercionAction.Fail)
            .setCoercion(CoercionInputShape.Object, CoercionAction.Fail);
    })
    .build();
TypeFactory typeFactory = objectMapper.getTypeFactory();

// Test.
JavaType arrayType = typeFactory.constructParametricType(List.class, String.class);
JavaType inputType = typeFactory.constructParametricType(Input.class, arrayType);
try {
    // Returns class java.lang.String + VALUE_NUMBER_INT -> correct.
    objectMapper.readValue("{ \"field\": [ 1 ] }", inputType);
    // Returns class java.util.ArrayList + START_ARRAY -> was expecting target type to be String.
    objectMapper.readValue("{ \"field\": [ [ 1 ] ] }", inputType);
    // Returns class java.util.ArrayList + START_OBJECT -> was expecting target type to be String.
    objectMapper.readValue("{ \"field\": [ { \"field\": 1 } ] }", inputType);
} catch (MismatchedInputException exception) {
    JsonParser parser = (JsonParser) exception.getProcessor();
    System.out.println(exception.getTargetType());
    System.out.println(parser.currentToken());
}

// A truly strict String parser.
// If we register this deserializer in the ObjectMapper above we will then get the expected target type.
public class StringDeserializer extends JsonDeserializer<String> {
    @Override
    public String deserialize(JsonParser parser, DeserializationContext context) throws IOException {
        if (!parser.hasToken(VALUE_STRING)) {
            throw context.wrongTokenException(parser, String.class, VALUE_STRING, null);
        }

        return parser.getText();
    }
}

This is our test suite for JSON strict parsing which we have used to open many such issues in the past, in case you want to take inspiration for Jackson tests.
Test.zip

[cowtowncoder]

Sounds like there is missing handling indeed, thank you for reporting this @joca-bt!

Unfortunately I don't think I have time to investigate this further right now; but I hope someone else could check it out; there should be enough information to dig into it.

Change itself should probably go in 2.16 branch since it changes exception messages that are part of existing behavior (even if fixing sub-optimal message).

[JooHyukKim]

I wrote a solution locally and the result seems reasonable.

May I ask you to review the error messages below and see if they are the expected ones before I make a PR, @joca-bt @cowtowncoder ?

Case : "{"field": [ 1 ] }"

Cannot coerce Integer value (1) to `java.lang.String` value (but could if coercion was enabled using `CoercionConfig`)
 at [Source: UNKNOWN; line: 1, column: 14] (through reference chain: com.fasterxml.jackson.databind.convert.DisableCoercions3690Test$Input3924["field"]->java.util.ArrayList[0])

Case : "{ "field": [ [ 1 ] ] }"

Cannot coerce Array value ([) to `java.lang.String` value (but could if coercion was enabled using `CoercionConfig`)
 at [Source: UNKNOWN; line: 1, column: 14] (through reference chain: com.fasterxml.jackson.databind.convert.DisableCoercions3690Test$Input3924["field"]->java.util.ArrayList[0])

Case : "{ "field": [ { "field": 1 } ] }"

Cannot coerce Object value ({) to `java.lang.String` value (but could if coercion was enabled using `CoercionConfig`)
 at [Source: UNKNOWN; line: 1, column: 14] (through reference chain: com.fasterxml.jackson.databind.convert.DisableCoercions3690Test$Input3924["field"]->java.util.ArrayList[0])

[cowtowncoder]

@JooHyukKim That looks good to me; coercion failure happening at element level, not for Array/List.

[JooHyukKim]

@cowtowncoder Thank you for the feedback! 🙏🏼🙏🏼 will make PR soon

[joca-bt]

For me in particular the message is irrelevant, we care about the exception fields having the right type, since we rely on that and not the messages.

[JooHyukKim]

For me in particular the message is irrelevant, we care about the exception fields having the right type, since we rely on that and not the messages.

@joca-bt Great point 👍🏻 I added assertion like below(or check the test I made on PR), does this prove to support your usecase?

 assertEquals(String.class, e.getTargetType());