fix: start turning on werror for code.

build.gradle

@@ -55,12 +55,34 @@ project.ext.externalDependency = [
 apply plugin: 'com.diffplug.spotless'
 apply plugin: 'org.shipkit.shipkit-auto-version'
 
+// TODO expand this to all projects and then delete this allow list. This list is letting us fix errors over time rather
+// than in one big change.
+def wErrorProjects = [
+    project(':core-models'),
+    // project(':dao-api'),
+    // project(':dao-api-impl'),
+    // project(':restli-resources'),
+    project(':testing'),
+    project(':validators')
+]
+
 allprojects {
   group = "com.linkedin.datahub-gma"
 
   apply plugin: 'idea'
   apply plugin: 'eclipse'
   apply plugin: 'checkstyle'
+
+  gradle.projectsEvaluated {
+    if (wErrorProjects.contains(project)) {
+      tasks.withType(JavaCompile) {
+        options.compilerArgs << "-Xlint:all" << "-Werror" <<
+            "-Xlint:-deprecation" << // TODO
+            "-Xlint:-processing" << // TODO we have annotations like @Nonnull that need a processor
+            "-Xlint:-serial" // I don't think we care about having custom Exception subclasses be serializable...
+      }
+    }
+  }
 }
 
 if (!project.hasProperty('disableShipkit')) {

core-models/src/main/javaPegasus/com/linkedin/common/urn/TupleKey.java

@@ -155,10 +155,7 @@ public <T> T getAs(int index, Class<T> clazz) {
     } else if (Long.TYPE.equals(clazz) || Long.class.equals(clazz)) {
       result = Long.valueOf(value);
     } else if (Enum.class.isAssignableFrom(clazz)) {
-      final Class<? extends Enum> enumClazz = clazz.asSubclass(Enum.class);
-      @SuppressWarnings("unchecked")
-      Enum<?> enumValue = Enum.valueOf(enumClazz, value);
-      result = enumValue;
+      result = getEnumValue(clazz, value);
     } else if (DataTemplateUtil.hasCoercer(clazz)) {
       result = DataTemplateUtil.coerceOutput(value, clazz);
     } else {
@@ -169,6 +166,15 @@ public <T> T getAs(int index, Class<T> clazz) {
     return rv;
   }
 
+  /**
+   * Helper method to capture E.
+   */
+  private <E extends Enum<E>> Enum<E> getEnumValue(Class<?> clazz, String value) {
+    @SuppressWarnings("unchecked")
+    final Class<E> enumClazz = (Class<E>) clazz.asSubclass(Enum.class);
+    return Enum.valueOf(enumClazz, value);
+  }
+
   public int size() {
     return _tuple.size();
   }

testing/test-models/src/main/javaPegasus/com/linkedin/testing/urn/BaseUrnCoercer.java

@@ -14,6 +14,7 @@ public Object coerceInput(T object) throws ClassCastException {
     return object.toString();
   }
 
+  @SuppressWarnings("unchecked")
   public T coerceOutput(Object object) throws TemplateOutputCastException {
     try {
       return (T) Urn.createFromString((String) object);

validators/src/main/java/com/linkedin/metadata/validator/SnapshotValidator.java

@@ -1,5 +1,6 @@
 package com.linkedin.metadata.validator;
 
+import com.linkedin.common.urn.Urn;
 import com.linkedin.data.schema.ArrayDataSchema;
 import com.linkedin.data.schema.DataSchema;
 import com.linkedin.data.schema.RecordDataSchema;
@@ -60,10 +61,11 @@ public static void validateSnapshotSchema(@Nonnull Class<? extends RecordTemplat
    *
    * @param snapshotClasses a collection of snapshot classes.
    */
-  public static void validateUniqueUrn(@Nonnull Collection<? extends Class> snapshotClasses) {
-    Set<Class> urnClasses = new HashSet<>();
+  public static void validateUniqueUrn(@Nonnull Collection<Class<? extends RecordTemplate>> snapshotClasses) {
+    final Set<Class<Urn>> urnClasses = new HashSet<>();
     snapshotClasses.forEach(snapshotClass -> {
-      Class urnClass = ValidationUtils.getUrnClass(ValidationUtils.getRecordSchema(snapshotClass).getField("urn"));
+      final Class<Urn> urnClass =
+          ValidationUtils.getUrnClass(ValidationUtils.getRecordSchema(snapshotClass).getField("urn"));
       if (urnClasses.contains(urnClass)) {
         ValidationUtils.invalidSchema("URN class %s in %s has already been claimed by another snapshot.", urnClass,
             snapshotClass);

validators/src/main/java/com/linkedin/metadata/validator/ValidationUtils.java

@@ -95,9 +95,12 @@ public static boolean isValidUrnField(@Nonnull RecordDataSchema.Field field, @No
   /**
    * Returns the Java class for an URN typeref field.
    */
-  public static Class getUrnClass(@Nonnull RecordDataSchema.Field field) {
+  public static Class<Urn> getUrnClass(@Nonnull RecordDataSchema.Field field) {
     try {
-      return Class.forName(((DataMap) field.getType().getProperties().get("java")).getString("class"));
+      @SuppressWarnings("unchecked")
+      final Class<Urn> clazz =
+          (Class<Urn>) Class.forName(((DataMap) field.getType().getProperties().get("java")).getString("class"));
+      return clazz;
     } catch (ClassNotFoundException e) {
       throw new RuntimeException(e);
     }