Description Michael Becker 2013-11-27 06:10:22 EST

JDT's null inference fails in the simple case of an intermediate variable between the null check of the object and the actual object usage. This is a problem expecially when using Xtend together with @NonNull/@Nullable annotations and strict checks, as Xtend generally creates Java code like:

Object input = InputSource.getInput(); // return value annotated as @Nullable
boolean _tripleNotEquals = (input != null);
if (_tripleNotEquals) {
    Object convert = Converter.convert(input); // parameter annotated with @NonNull
}

In this example, it is clearly apparent that input can never be null in line 4. However, the JDT infers the input as potentially null / @Nullable and creates an error if the "Conflict between null annotations and null inference" preference is set to "Error".

Steps to Reproduce:

1) Preparation:
- go to Preferences | Java | Compiler | Errors/Warnings | Null Analysis
- check "Enable annotation-based null analysis"
- set "Conflict between null annotations and null inference" to "Error"

2) create Java class:

package test;

import java.util.Random;
import org.eclipse.jdt.annotation.NonNull;
import org.eclipse.jdt.annotation.Nullable;

public class Example
{
    @Nullable
    public Object getInput()
    {
        return new Random().nextBoolean() ? new Object() : null;
    }

    @NonNull
    public Object convert(@NonNull final Object input)
    {
        return input;
    }

    public void perform()
    {
        final Object input = getInput();
        final boolean notNull = (input != null);
        if (notNull)
        {
            // leads to error "Null type mismatch: required '@NonNull Object' but the provided value is inferred as @Nullable"
            final Object converted = convert(input);
        }
    }
}