Recognize that <T extends @nullable Object> implies nullability.

If you have a method with a parameter of type `T`, we should not expect it to
throw an exception when called with null.

RELNOTES=In NullPointerTester, a parameter of type `<T extends @nullable Object>` is allowed to be null.
PiperOrigin-RevId: 367051816

Author: eamonnmcmanus

android/guava-testlib/src/com/google/common/testing/NullPointerTester.java

@@ -52,7 +52,7 @@
 /**
  * A test utility that verifies that your methods and constructors throw {@link
  * NullPointerException} or {@link UnsupportedOperationException} whenever null is passed to a
- * parameter that isn't annotated with an annotation with the simple name {@code Nullable}, {@lcode
+ * parameter that isn't annotated with an annotation with the simple name {@code Nullable}, {@code
  * CheckForNull}, {@link NullableType}, or {@link NullableDecl}.
  *
  * <p>The tested methods and constructors are invoked -- each time with one parameter being null and

guava-testlib/src/com/google/common/testing/NullPointerTester.java

@@ -34,16 +34,19 @@
 import com.google.common.reflect.Reflection;
 import com.google.common.reflect.TypeToken;
 import java.lang.annotation.Annotation;
+import java.lang.reflect.AnnotatedType;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Member;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
+import java.lang.reflect.TypeVariable;
 import java.util.Arrays;
 import java.util.List;
 import java.util.concurrent.ConcurrentMap;
+import java.util.function.Function;
 import junit.framework.Assert;
 import junit.framework.AssertionFailedError;
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -52,7 +55,7 @@
  * A test utility that verifies that your methods and constructors throw {@link
  * NullPointerException} or {@link UnsupportedOperationException} whenever null is passed to a
  * parameter whose declaration or type isn't annotated with an annotation with the simple name
- * {@code Nullable}, {@lcode CheckForNull}, {@link NullableType}, or {@link NullableDecl}.
+ * {@code Nullable}, {@code CheckForNull}, {@link NullableType}, or {@link NullableDecl}.
  *
  * <p>The tested methods and constructors are invoked -- each time with one parameter being null and
  * the rest not null -- and the test fails if no expected exception is thrown. {@code
@@ -483,7 +486,22 @@ static boolean isNullable(Invokable<?, ?> invokable) {
 
   static boolean isNullable(Parameter param) {
     return isNullable(param.getAnnotatedType().getAnnotations())
-        || isNullable(param.getAnnotations());
+        || isNullable(param.getAnnotations())
+        || isNullableTypeVariable(param.getAnnotatedType().getType());
+  }
+
+  private static boolean isNullableTypeVariable(Type type) {
+    if (!(type instanceof TypeVariable)) {
+      return false;
+    }
+    TypeVariable<?> var = (TypeVariable<?>) type;
+    AnnotatedType[] bounds = GET_ANNOTATED_BOUNDS.apply(var);
+    for (AnnotatedType bound : bounds) {
+      if (isNullable(bound.getAnnotations()) || isNullableTypeVariable(bound.getType())) {
+        return true;
+      }
+    }
+    return false;
   }
 
   private static boolean isNullable(Annotation[] annotations) {
@@ -495,6 +513,27 @@ private static boolean isNullable(Annotation[] annotations) {
     return false;
   }
 
+  // This is currently required because of j2objc restrictions.
+  private static final Function<TypeVariable<?>, AnnotatedType[]> GET_ANNOTATED_BOUNDS =
+      initGetAnnotatedBounds();
+
+  private static Function<TypeVariable<?>, AnnotatedType[]> initGetAnnotatedBounds() {
+    AnnotatedType[] noBounds = new AnnotatedType[0];
+    Method getAnnotatedBounds;
+    try {
+      getAnnotatedBounds = TypeVariable.class.getMethod("getAnnotatedBounds");
+    } catch (ReflectiveOperationException e) {
+      return v -> noBounds;
+    }
+    return v -> {
+      try {
+        return (AnnotatedType[]) getAnnotatedBounds.invoke(v);
+      } catch (ReflectiveOperationException e) {
+        return noBounds;
+      }
+    };
+  }
+
   private boolean isIgnored(Member member) {
     return member.isSynthetic() || ignoredMembers.contains(member) || isEquals(member);
   }

guava-testlib/test/com/google/common/testing/NullPointerTesterTest.java

@@ -1484,4 +1484,47 @@ public void testConstructor_ShouldFail() throws Exception {
     }
     fail("Should detect problem in " + FailOnOneOfTwoConstructors.class.getSimpleName());
   }
+
+  public static class NullBounds<T extends @Nullable Object, U extends T, X> {
+    boolean xWasCalled;
+
+    @SuppressWarnings("unused") // Called by reflection
+    public void x(X x) {
+      xWasCalled = true;
+      checkNotNull(x);
+    }
+
+    @SuppressWarnings("unused") // Called by reflection
+    public void t(T t) {
+      fail("Method with parameter <T extends @Nullable Object> should not be called");
+    }
+
+    @SuppressWarnings("unused") // Called by reflection
+    public void u(U u) {
+      fail(
+          "Method with parameter <U extends T> where <T extends @Nullable Object> should not be"
+              + " called");
+    }
+
+    @SuppressWarnings("unused") // Called by reflection
+    public <A extends @Nullable Object> void a(A a) {
+      fail("Method with parameter <A extends @Nullable Object> should not be called");
+    }
+
+    @SuppressWarnings("unused") // Called by reflection
+    public <A extends B, B extends @Nullable Object> void b(A a) {
+      fail(
+          "Method with parameter <A extends B> where <B extends @Nullable Object> should not be"
+              + " called");
+    }
+  }
+
+  public void testNullBounds() {
+    // NullBounds has methods whose parameters are type variables that have
+    // "extends @Nullable Object" as a bound. This test ensures that NullPointerTester considers
+    // those parameters to be @Nullable, so it won't call the methods.
+    NullBounds<?, ?, ?> nullBounds = new NullBounds<>();
+    new NullPointerTester().testAllPublicInstanceMethods(nullBounds);
+    assertThat(nullBounds.xWasCalled).isTrue();
+  }
 }