Add nullability annotations, remove @PublicApi annotations for RTDB. (#603)

* Add missing nullability annotations to RTDB.

* Remove redundant `@PublicApi` annotations.

* Update changelog.

Author: vkryachko

firebase-database/CHANGELOG.md

@@ -5,7 +5,10 @@
 - [changed] Improved error messages for certain Number types that are not
   supported by our serialization layer (#272).
 - [internal] Updated the SDK initialization process and removed usages of
-  deprecated method
+  deprecated method.
+- [changed] Added missing nullability annotations for better Kotlin interop.
+- [internal] Removed ``@PublicApi` annotations as they are no longer enforced
+  and have no semantic meaning.
 
 # 16.0.6  
 - [fixed] Fixed an issue that could cause a NullPointerException during the

firebase-database/firebase-database.gradle

@@ -19,7 +19,6 @@ plugins {
 firebaseLibrary {
     testLab.enabled = true
     publishSources = true
-    staticAnalysis.disableKotlinInteropLint()
 }
 
 android {

firebase-database/src/main/java/com/google/firebase/database/ChildEventListener.java

@@ -16,15 +16,13 @@
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
-import com.google.firebase.annotations.PublicApi;
 
 /**
  * Classes implementing this interface can be used to receive events about changes in the child
  * locations of a given {@link DatabaseReference DatabaseReference} ref. Attach the listener to a
  * location using {@link DatabaseReference#addChildEventListener(ChildEventListener)} and the
  * appropriate method will be triggered when changes occur.
  */
-@PublicApi
 public interface ChildEventListener {
 
   /**
@@ -35,7 +33,6 @@ public interface ChildEventListener {
    * @param previousChildName The key name of sibling location ordered before the new child. This
    *     will be null for the first child node of a location.
    */
-  @PublicApi
   public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName);
 
   /**
@@ -45,7 +42,6 @@ public interface ChildEventListener {
    * @param previousChildName The key name of sibling location ordered before the child. This will
    *     be null for the first child node of a location.
    */
-  @PublicApi
   public void onChildChanged(@NonNull DataSnapshot snapshot, @Nullable String previousChildName);
 
   /**
@@ -54,7 +50,6 @@ public interface ChildEventListener {
    *
    * @param snapshot An immutable snapshot of the data at the child that was removed.
    */
-  @PublicApi
   public void onChildRemoved(@NonNull DataSnapshot snapshot);
 
   /**
@@ -67,7 +62,6 @@ public interface ChildEventListener {
    * @param previousChildName The key name of the sibling location ordered before the child
    *     location. This will be null if this location is ordered first.
    */
-  @PublicApi
   public void onChildMoved(@NonNull DataSnapshot snapshot, @Nullable String previousChildName);
 
   /**
@@ -78,6 +72,5 @@ public interface ChildEventListener {
    *
    * @param error A description of the error that occurred
    */
-  @PublicApi
   public void onCancelled(@NonNull DatabaseError error);
 }

firebase-database/src/main/java/com/google/firebase/database/DataSnapshot.java

@@ -16,7 +16,6 @@
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
-import com.google.firebase.annotations.PublicApi;
 import com.google.firebase.database.core.Path;
 import com.google.firebase.database.core.utilities.Validation;
 import com.google.firebase.database.core.utilities.encoding.CustomClassMapper;
@@ -39,7 +38,6 @@
  * DatabaseReference DatabaseReference} reference (e.g. with {@link
  * DatabaseReference#setValue(Object)}).
  */
-@PublicApi
 public class DataSnapshot {
 
   private final IndexedNode node;
@@ -63,7 +61,6 @@ public class DataSnapshot {
    * @return The DataSnapshot for the child location
    */
   @NonNull
-  @PublicApi
   public DataSnapshot child(@NonNull String path) {
     DatabaseReference childRef = query.child(path);
     Node childNode = this.node.getNode().getChild(new Path(path));
@@ -76,7 +73,6 @@ public DataSnapshot child(@NonNull String path) {
    * @param path A relative path to the location of child data
    * @return Whether or not the specified child location has data
    */
-  @PublicApi
   public boolean hasChild(@NonNull String path) {
     if (query.getParent() == null) {
       Validation.validateRootPathString(path);
@@ -91,7 +87,6 @@ public boolean hasChild(@NonNull String path) {
    *
    * @return True if the snapshot has any children, otherwise false
    */
-  @PublicApi
   public boolean hasChildren() {
     return node.getNode().getChildCount() > 0;
   }
@@ -101,7 +96,6 @@ public boolean hasChildren() {
    *
    * @return True if the snapshot contains a non-null value, otherwise false
    */
-  @PublicApi
   public boolean exists() {
     return !node.getNode().isEmpty();
   }
@@ -126,7 +120,6 @@ public boolean exists() {
    *     location.
    */
   @Nullable
-  @PublicApi
   public Object getValue() {
     return node.getNode().getValue();
   }
@@ -156,7 +149,6 @@ public Object getValue() {
    *     location.
    */
   @Nullable
-  @PublicApi
   public Object getValue(boolean useExportFormat) {
     return node.getNode().getValue(useExportFormat);
   }
@@ -206,7 +198,6 @@ public Object getValue(boolean useExportFormat) {
    *     if there is no data at this location.
    */
   @Nullable
-  @PublicApi
   public <T> T getValue(@NonNull Class<T> valueType) {
     Object value = node.getNode().getValue();
     return CustomClassMapper.convertToCustomClass(value, valueType);
@@ -233,14 +224,12 @@ public <T> T getValue(@NonNull Class<T> valueType) {
    *     there is no data at this location.
    */
   @Nullable
-  @PublicApi
   public <T> T getValue(@NonNull GenericTypeIndicator<T> t) {
     Object value = node.getNode().getValue();
     return CustomClassMapper.convertToCustomClass(value, t);
   }
 
   /** @return The number of immediate children in the this snapshot */
-  @PublicApi
   public long getChildrenCount() {
     return node.getNode().getChildCount();
   }
@@ -251,7 +240,6 @@ public long getChildrenCount() {
    * @return A DatabaseReference corresponding to the location that this snapshot came from
    */
   @NonNull
-  @PublicApi
   public DatabaseReference getRef() {
     return query;
   }
@@ -261,7 +249,6 @@ public DatabaseReference getRef() {
    *     to the database root.
    */
   @Nullable
-  @PublicApi
   public String getKey() {
     return query.getKey();
   }
@@ -277,7 +264,6 @@ public String getKey() {
    * @return The immediate children of this snapshot
    */
   @NonNull
-  @PublicApi
   public Iterable<DataSnapshot> getChildren() {
     final Iterator<NamedNode> iter = node.iterator();
     return new Iterable<DataSnapshot>() {
@@ -321,7 +307,6 @@ public void remove() {
    * @return the priority of the data contained in this snapshot as a native type
    */
   @Nullable
-  @PublicApi
   public Object getPriority() {
     Object priority = node.getNode().getPriority().getValue();
     if (priority instanceof Long) {

firebase-database/src/main/java/com/google/firebase/database/DatabaseError.java

@@ -16,7 +16,6 @@
 
 import androidx.annotation.NonNull;
 import androidx.annotation.RestrictTo;
-import com.google.firebase.annotations.PublicApi;
 import java.io.PrintWriter;
 import java.io.StringWriter;
 import java.util.HashMap;
@@ -26,49 +25,48 @@
  * Instances of DatabaseError are passed to callbacks when an operation failed. They contain a
  * description of the specific error that occurred.
  */
-@PublicApi
 public class DatabaseError {
 
   /** <strong>Internal use</strong> */
-  @PublicApi public static final int DATA_STALE = -1;
+  public static final int DATA_STALE = -1;
   /** The server indicated that this operation failed */
-  @PublicApi public static final int OPERATION_FAILED = -2;
+  public static final int OPERATION_FAILED = -2;
   /** This client does not have permission to perform this operation */
-  @PublicApi public static final int PERMISSION_DENIED = -3;
+  public static final int PERMISSION_DENIED = -3;
   /** The operation had to be aborted due to a network disconnect */
-  @PublicApi public static final int DISCONNECTED = -4;
+  public static final int DISCONNECTED = -4;
 
   // Preempted was removed, this is for here for completeness and history
   // public static final int PREEMPTED = -5;
 
   /** The supplied auth token has expired */
-  @PublicApi public static final int EXPIRED_TOKEN = -6;
+  public static final int EXPIRED_TOKEN = -6;
   /**
    * The specified authentication token is invalid. This can occur when the token is malformed,
    * expired, or the secret that was used to generate it has been revoked.
    */
-  @PublicApi public static final int INVALID_TOKEN = -7;
+  public static final int INVALID_TOKEN = -7;
   /** The transaction had too many retries */
-  @PublicApi public static final int MAX_RETRIES = -8;
+  public static final int MAX_RETRIES = -8;
   /** The transaction was overridden by a subsequent set */
-  @PublicApi public static final int OVERRIDDEN_BY_SET = -9;
+  public static final int OVERRIDDEN_BY_SET = -9;
   /** The service is unavailable */
-  @PublicApi public static final int UNAVAILABLE = -10;
+  public static final int UNAVAILABLE = -10;
   /** An exception occurred in user code */
-  @PublicApi public static final int USER_CODE_EXCEPTION = -11;
+  public static final int USER_CODE_EXCEPTION = -11;
 
   // client codes
   /** The operation could not be performed due to a network error. */
-  @PublicApi public static final int NETWORK_ERROR = -24;
+  public static final int NETWORK_ERROR = -24;
 
   /** The write was canceled locally */
-  @PublicApi public static final int WRITE_CANCELED = -25;
+  public static final int WRITE_CANCELED = -25;
 
   /**
    * An unknown error occurred. Please refer to the error message and error details for more
    * information.
    */
-  @PublicApi public static final int UNKNOWN_ERROR = -999;
+  public static final int UNKNOWN_ERROR = -999;
 
   private static final Map<Integer, String> errorReasons = new HashMap<Integer, String>();
 
@@ -175,8 +173,8 @@ public static DatabaseError fromStatus(String status, String reason, String deta
     return new DatabaseError(code, message, details);
   }
 
-  @PublicApi
-  public static DatabaseError fromException(Throwable e) {
+  @NonNull
+  public static DatabaseError fromException(@NonNull Throwable e) {
     StringWriter stringWriter = new StringWriter();
     PrintWriter printWriter = new PrintWriter(stringWriter);
     e.printStackTrace(printWriter);
@@ -199,21 +197,18 @@ private DatabaseError(int code, String message, String details) {
   }
 
   /** @return One of the defined status codes, depending on the error */
-  @PublicApi
   public int getCode() {
     return code;
   }
 
   /** @return A human-readable description of the error */
   @NonNull
-  @PublicApi
   public String getMessage() {
     return message;
   }
 
   /** @return Human-readable details on the error and additional information, e.g. links to docs; */
   @NonNull
-  @PublicApi
   public String getDetails() {
     return details;
   }
@@ -229,7 +224,7 @@ public String toString() {
    *
    * @return An exception wrapping this error, with an appropriate message and no stack trace.
    */
-  @PublicApi
+  @NonNull
   public DatabaseException toException() {
     return new DatabaseException("Firebase Database error: " + message);
   }

firebase-database/src/main/java/com/google/firebase/database/DatabaseException.java

@@ -15,13 +15,11 @@
 package com.google.firebase.database;
 
 import androidx.annotation.RestrictTo;
-import com.google.firebase.annotations.PublicApi;
 
 /**
  * This error is thrown when the Firebase Database library is unable to operate on the input it has
  * been given.
  */
-@PublicApi
 public class DatabaseException extends RuntimeException {
 
   /**