NullPointerTester should not require @nullable on the param of an equ…

…als() override

This is currently being worked around with things like:

new NullPointerTester()
    .ignore(AutoValue_MyValueType.class.getMethod("equals", Object.class))
    ...

The work-arounds prevent AutoValue from being treated as a pure implementation-generating processor.

Fixes #1819

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=131074329

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

@@ -469,7 +469,37 @@ private static boolean isNullable(Parameter param) {
   }
 
   private boolean isIgnored(Member member) {
-    return member.isSynthetic() || ignoredMembers.contains(member);
+    return member.isSynthetic() || ignoredMembers.contains(member) || isEquals(member);
+  }
+
+  /**
+   * Returns true if the the given member is a method that overrides {@link Object#equals(Object)}.
+   *
+   * <p>The documentation for {@link Object#equals} says it should accept null, so don't require an
+   * explicit {@link @Nullable} annotation (see <a
+   * href="https://github.com/google/guava/issues/1819">#1819</a>).
+   *
+   * <p>It is not necessary to consider visibility, return type, or type parameter declarations. The
+   * declaration of a method with the same name and formal parameters as {@link Object#equals} that
+   * is not public and boolean-returning, or that declares any type parameters, would be rejected at
+   * compile-time.
+   */
+  private static boolean isEquals(Member member) {
+    if (!(member instanceof Method)) {
+      return false;
+    }
+    Method method = (Method) member;
+    if (!method.getName().contentEquals("equals")) {
+      return false;
+    }
+    Class<?>[] parameters = method.getParameterTypes();
+    if (parameters.length != 1) {
+      return false;
+    }
+    if (!parameters[0].equals(Object.class)) {
+      return false;
+    }
+    return true;
   }
 
   /**

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

@@ -1300,4 +1300,22 @@ public void testNonStaticInnerClass() {
   private static String rootLocaleFormat(String format, Object... args) {
     return String.format(Locale.ROOT, format, args);
   }
+
+  static class OverridesEquals {
+    @Override
+    public boolean equals(Object o) {
+      return true;
+    }
+  }
+
+  static class DoesNotOverrideEquals {
+    public boolean equals(Object a, Object b) {
+      return true;
+    }
+  }
+
+  public void testEqualsMethod() {
+    shouldPass(new OverridesEquals());
+    shouldFail(new DoesNotOverrideEquals());
+  }
 }