Enable more error-prone checks

Align all checks with the settings in the Gerrit project, with the
exception of:

 - ImmutableEnumChecker
 - ReferenceEquality

which remain as WARN. These will be fixed (or suppressed) in follow-up
changes.

Change-Id: I05e96e10928cbfe2796f68357cbb4abc53374ee6

tools/BUILD

diff --git a/tools/BUILD b/tools/BUILD
index 9533a6d..6d15a21 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -22,64 +22,66 @@
     name = "error_prone",
     javacopts = [
         "-XepDisableWarningsInGeneratedCode",
-        "-Xep:MissingCasesInEnumSwitch:ERROR",
-        "-Xep:ReferenceEquality:WARN",
-        "-Xep:StringEquality:WARN",
-        "-Xep:WildcardImport:WARN",
-        "-Xep:AmbiguousMethodReference:WARN",
-        "-Xep:BadAnnotationImplementation:WARN",
-        "-Xep:BadComparable:WARN",
+        "-Xep:AmbiguousMethodReference:ERROR",
+        "-Xep:BadAnnotationImplementation:ERROR",
+        "-Xep:BadComparable:ERROR",
         "-Xep:BoxedPrimitiveConstructor:ERROR",
-        "-Xep:CannotMockFinalClass:WARN",
-        "-Xep:ClassCanBeStatic:WARN",
-        "-Xep:ClassNewInstance:WARN",
+        "-Xep:CannotMockFinalClass:ERROR",
+        "-Xep:ClassCanBeStatic:ERROR",
+        "-Xep:ClassNewInstance:ERROR",
         "-Xep:DefaultCharset:ERROR",
-        "-Xep:DoubleCheckedLocking:WARN",
-        "-Xep:ElementsCountedInLoop:WARN",
-        "-Xep:EqualsHashCode:WARN",
-        "-Xep:EqualsIncompatibleType:WARN",
-        "-Xep:ExpectedExceptionChecker:WARN",
-        "-Xep:Finally:WARN",
-        "-Xep:FloatingPointLiteralPrecision:WARN",
-        "-Xep:FragmentInjection:WARN",
-        "-Xep:FragmentNotInstantiable:WARN",
-        "-Xep:FunctionalInterfaceClash:WARN",
-        "-Xep:FutureReturnValueIgnored:WARN",
-        "-Xep:GetClassOnEnum:WARN",
+        "-Xep:DoubleCheckedLocking:ERROR",
+        "-Xep:ElementsCountedInLoop:ERROR",
+        "-Xep:DoubleCheckedLocking:ERROR",
+        "-Xep:ElementsCountedInLoop:ERROR",
+        "-Xep:EqualsHashCode:ERROR",
+        "-Xep:EqualsIncompatibleType:ERROR",
+        "-Xep:ExpectedExceptionChecker:ERROR",
+        "-Xep:Finally:ERROR",
+        "-Xep:FloatingPointLiteralPrecision:ERROR",
+        "-Xep:FragmentInjection:ERROR",
+        "-Xep:FragmentNotInstantiable:ERROR",
+        "-Xep:FunctionalInterfaceClash:ERROR",
+        "-Xep:FutureReturnValueIgnored:ERROR",
+        "-Xep:GetClassOnEnum:ERROR",
         "-Xep:ImmutableAnnotationChecker:WARN",
         "-Xep:ImmutableEnumChecker:WARN",
-        "-Xep:IncompatibleModifiers:WARN",
-        "-Xep:InjectOnConstructorOfAbstractClass:WARN",
-        "-Xep:InputStreamSlowMultibyteRead:WARN",
-        "-Xep:IterableAndIterator:WARN",
-        "-Xep:JUnit3FloatingPointComparisonWithoutDelta:WARN",
-        "-Xep:JUnitAmbiguousTestClass:WARN",
-        "-Xep:LiteralClassName:WARN",
-        "-Xep:MissingFail:WARN",
-        "-Xep:MissingOverride:WARN",
-        "-Xep:MutableConstantField:WARN",
-        "-Xep:NarrowingCompoundAssignment:WARN",
-        "-Xep:NonAtomicVolatileUpdate:WARN",
-        "-Xep:NonOverridingEquals:WARN",
-        "-Xep:NullableConstructor:WARN",
-        "-Xep:NullablePrimitive:WARN",
-        "-Xep:NullableVoid:WARN",
-        "-Xep:OperatorPrecedence:WARN",
-        "-Xep:OverridesGuiceInjectableMethod:WARN",
-        "-Xep:PreconditionsInvalidPlaceholder:WARN",
-        "-Xep:ProtoFieldPreconditionsCheckNotNull:WARN",
-        "-Xep:ProtocolBufferOrdinal:WARN",
-        "-Xep:RequiredModifiers:WARN",
-        "-Xep:ShortCircuitBoolean:WARN",
-        "-Xep:SimpleDateFormatConstant:WARN",
-        "-Xep:StaticGuardedByInstance:WARN",
-        "-Xep:SynchronizeOnNonFinalField:WARN",
-        "-Xep:TruthConstantAsserts:WARN",
-        "-Xep:TypeParameterShadowing:WARN",
-        "-Xep:TypeParameterUnusedInFormals:WARN",
-        "-Xep:URLEqualsHashCode:WARN",
-        "-Xep:UnsynchronizedOverridesSynchronized:WARN",
-        "-Xep:WaitNotInLoop:WARN",
+        "-Xep:IncompatibleModifiers:ERROR",
+        "-Xep:InjectOnConstructorOfAbstractClass:ERROR",
+        "-Xep:InputStreamSlowMultibyteRead:ERROR",
+        "-Xep:IterableAndIterator:ERROR",
+        "-Xep:JUnit3FloatingPointComparisonWithoutDelta:ERROR",
+        "-Xep:JUnitAmbiguousTestClass:ERROR",
+        "-Xep:LiteralClassName:ERROR",
+        "-Xep:MissingCasesInEnumSwitch:ERROR",
+        "-Xep:MissingFail:ERROR",
+        "-Xep:MissingOverride:ERROR",
+        "-Xep:MutableConstantField:ERROR",
+        "-Xep:NarrowingCompoundAssignment:ERROR",
+        "-Xep:NonAtomicVolatileUpdate:ERROR",
+        "-Xep:NonOverridingEquals:ERROR",
+        "-Xep:NullableConstructor:ERROR",
+        "-Xep:NullablePrimitive:ERROR",
+        "-Xep:NullableVoid:ERROR",
+        "-Xep:OperatorPrecedence:ERROR",
+        "-Xep:OverridesGuiceInjectableMethod:ERROR",
+        "-Xep:PreconditionsInvalidPlaceholder:ERROR",
+        "-Xep:ProtoFieldPreconditionsCheckNotNull:ERROR",
+        "-Xep:ProtocolBufferOrdinal:ERROR",
+        "-Xep:ReferenceEquality:WARN",
+        "-Xep:RequiredModifiers:ERROR",
+        "-Xep:ShortCircuitBoolean:ERROR",
+        "-Xep:SimpleDateFormatConstant:ERROR",
+        "-Xep:StaticGuardedByInstance:ERROR",
+        "-Xep:StringEquality:ERROR",
+        "-Xep:SynchronizeOnNonFinalField:ERROR",
+        "-Xep:TruthConstantAsserts:ERROR",
+        "-Xep:TypeParameterShadowing:ERROR",
+        "-Xep:TypeParameterUnusedInFormals:ERROR",
+        "-Xep:URLEqualsHashCode:ERROR",
+        "-Xep:UnsynchronizedOverridesSynchronized:ERROR",
+        "-Xep:WaitNotInLoop:ERROR",
+        "-Xep:WildcardImport:ERROR",
     ],
     packages = ["error_prone_packages"],
 )